external entity expansion Safe (5) Safe (2) Safe (3) Safe (5) Safe (4)

`DTD`_ retrieval Safe (5) Safe Safe Safe (5) Safe

decompression bomb Safe Safe Safe Safe **Vulnerable**

large tokens **Vulnerable** (6) **Vulnerable** (6) **Vulnerable** (6) **Vulnerable** (6) **Vulnerable** (6)

1. Expat 2.4.1 and newer is not vulnerable to the "billion laughs" and

4. :mod:`xmlrpc.client` doesn't expand external entities and omits them.

5. Since Python 3.7.1, external general entities are no longer processed by

default.

6. Expat 2.6.0 and newer is not vulnerable to denial of service

through quadratic runtime caused by parsing large tokens.

Items still listed as vulnerable due to

potential reliance on system-provided libraries. Check

:const:`!pyexpat.EXPAT_VERSION`.

billion laughs / exponential entity expansion

files. For an attacker it can reduce the amount of transmitted data by three

magnitudes or more.

large tokens

Expat needs to re-parse unfinished tokens; without the protection

introduced in Expat 2.6.0, this can lead to quadratic runtime that can

be used to cause denial of service in the application parsing XML.

The issue is known as

`CVE-2023-52425 <https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2023-52425>`_.

The documentation for `defusedxml`_ on PyPI has further information about

all known attack vectors with examples and references.