In Mozilla Bleach before 3.12, a mutation XSS in bleach.clean when RCDATA and either svg or math tags are whitelisted and the keyword argument strip=False.

The remote Ubuntu 16.04 LTS / 18.04 LTS / 20.04 LTS host has packages installed that are affected by multiple vulnerabilities as referenced in the USN-8077-1 advisory.

    It was discovered that Bleach did not properly sanitize URI attributes containing character entities. An     attacker could possibly use this issue to construct a URI with a disallowed scheme that would bypass     sanitization, leading to cross-site scripting. This issue only affected Ubuntu 18.04 LTS. (CVE-2018-7753)

    Yaniv Nizry discovered that Bleach was vulnerable to a mutation cross-site scripting issue when sanitizing     HTML with the noscript tag and a raw tag in the allowed tags list. An attacker could possibly use this     issue to inject malicious content, leading to cross-site scripting. This issue only affected Ubuntu 18.04     LTS. (CVE-2020-6802)

    Yaniv Nizry discovered that Bleach was vulnerable to a mutation cross-site scripting issue when sanitizing     HTML with RCDATA together with svg or math tags in the allowed tags list. An attacker could possibly use     this issue to inject malicious content, leading to cross-site scripting. (CVE-2020-6816)

    It was discovered that Bleach incorrectly handled parsing of style attributes when sanitizing HTML. An     attacker could possibly use this issue to perform a regular expression denial of service, leading to     excessive resource consumption. (CVE-2020-6817)

    Yaniv Nizry and Micha Bentkowski discovered that Bleach was vulnerable to a mutation cross-site     scripting issue when sanitizing HTML with certain combinations of allowed tags. An attacker could possibly     use this issue to inject malicious content, leading to cross-site scripting. (CVE-2021-23980)

Tenable has extracted the preceding description block directly from the Ubuntu security advisory.

Note that Nessus has not tested for these issues but has instead relied only on the application's self-reported version number.

This update for python-bleach fixes the following issues :

  - CVE-2021-23980: Fixed mutation XSS on bleach.clean with     specific combinations of allowed tags (boo#1184547)

Update to 3.1.5 :

  - replace missing ``setuptools`` dependency with     ``packaging``. Thank you Benjamin Peterson.

Update to 3.1.4 (boo#1168280, CVE-2020-6817) :

  - ``bleach.clean`` behavior parsing style attributes could     result in a regular expression denial of service     (ReDoS). Calls to ``bleach.clean`` with an allowed tag     with an allowed ``style`` attribute were vulnerable to     ReDoS. For example, ``bleach.clean(..., attributes=('a':
    ['style']))``.

  - Style attributes with dashes, or single or double quoted     values are cleaned instead of passed through.

update to 3.1.3 (boo#1167379, CVE-2020-6816) :

  - Add relative link to code of conduct. (#442)

  - Drop deprecated 'setup.py test' support. (#507)

  - Fix typo: curren -> current in tests/test_clean.py     (#504)

  - Test on PyPy 7

  - Drop test support for end of life Python 3.4

  - ``bleach.clean`` behavior parsing embedded MathML and     SVG content with RCDATA tags did not match browser     behavior and could result in a mutation XSS. Calls to     ``bleach.clean`` with ``strip=False`` and ``math`` or     ``svg`` tags and one or more of the RCDATA tags     ``script``, ``noscript``, ``style``, ``noframes``,     ``iframe``, ``noembed``, or ``xmp`` in the allowed tags     whitelist were vulnerable to a mutation XSS.

It was reported that python-bleach, a whitelist-based HTML-sanitizing library, is prone to a mutation XSS vulnerability in bleach.clean when strip=False and 'math' or 'svg' tags and one or more of the RCDATA tags were whitelisted.

ID	Name	Product	Family	Severity
301534	Ubuntu 16.04 LTS / 18.04 LTS / 20.04 LTS : Bleach vulnerabilities (USN-8077-1)	Nessus	Ubuntu Local Security Checks	critical
148606	openSUSE Security Update : python-bleach (openSUSE-2021-552)	Nessus	SuSE Local Security Checks	medium
134773	Debian DSA-4643-1 : python-bleach - security update	Nessus	Debian Local Security Checks	medium

Detections

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CVE-2020-6816

medium

Tenable Plugins

critical

medium

medium