Xss fix - #40136
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mhevery
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☹️ Sorry, but only Googlers may change the label cla: yes. |
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jelbourn
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LGTM
Reviewed-for: fw-security
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packages/core/test/acceptance/security_spec.ts
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packages/core/test/acceptance/security_spec.ts
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packages/core/test/util/dom_spec.ts
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AndrewKushnir
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LGTM, thanks for the fix @mhevery 👍
(just left a couple minor comments related to comments, nothing critical)
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packages/core/test/acceptance/security_spec.ts
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packages/core/src/util/dom.ts
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Escape the content of the strings so that it can be safely inserted into a comment node. The issue is that HTML does not specify any way to escape comment end text inside the comment. `<!-- The way you close a comment is with "-->". -->`. Above the `"-->"` is meant to be text not an end to the comment. This can be created programmatically through DOM APIs. ``` div.innerHTML = div.innerHTML ``` One would expect that the above code would be safe to do, but it turns out that because comment text is not escaped, the comment may contain text which will prematurely close the comment opening up the application for XSS attack. (In SSR we programmatically create comment nodes which may contain such text and expect them to be safe.) This function escapes the comment text by looking for the closing char sequence `-->` and replace it with `-_-_>` where the `_` is a zero width space `\u200B`. The result is that if a comment contains `-->` text it will render normally but it will not cause the HTML parser to close the comment.
gkalpak
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Dec 16, 2020
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packages/core/src/util/dom.ts
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| const END_COMMENT = /-->/g; | ||
| const END_COMMENT_ESCAPED = '-\u200B-\u200B>'; |
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OOC, why use two \u200Bs? Wouldn't --\u200B> also work?
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alxhub
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Escape the content of the strings so that it can be safely inserted into a comment node. The issue is that HTML does not specify any way to escape comment end text inside the comment. `<!-- The way you close a comment is with "-->". -->`. Above the `"-->"` is meant to be text not an end to the comment. This can be created programmatically through DOM APIs. ``` div.innerHTML = div.innerHTML ``` One would expect that the above code would be safe to do, but it turns out that because comment text is not escaped, the comment may contain text which will prematurely close the comment opening up the application for XSS attack. (In SSR we programmatically create comment nodes which may contain such text and expect them to be safe.) This function escapes the comment text by looking for the closing char sequence `-->` and replace it with `-_-_>` where the `_` is a zero width space `\u200B`. The result is that if a comment contains `-->` text it will render normally but it will not cause the HTML parser to close the comment. PR Close #40136
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Escape the content of the strings so that it can be safely inserted into a comment node.
The issue is that HTML does not specify any way to escape comment end text inside the comment. <!-- The way you close a comment is with "-->". -->. Above the "-->" is meant to be text not an end to the comment. This can be created programmatically through DOM APIs.
One would expect that the above code would be safe to do, but it turns out that because comment text is not escaped, the comment may contain text which will prematurely close the comment opening up the application for XSS attack. (In SSR we programmatically create comment nodes which may contain such text and expect them to be safe.)
This function escapes the comment text by looking for the closing char sequence --> and replace it with -_-_> where the _ is a zero width space \u200B. The result is that if a comment contains --> text it will render normally but it will not cause the HTML parser to close the comment.
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