CVE-2021-28957

Name	CVE-2021-28957
Description	An XSS vulnerability was discovered in python-lxml's clean module versions before 4.6.3. When disabling the safe_attrs_only and forms arguments, the Cleaner class does not remove the formaction attribute allowing for JS to bypass the sanitizer. A remote attacker could exploit this flaw to run arbitrary JS code on users who interact with incorrectly sanitized HTML. This issue is patched in lxml 4.6.3.
Source	CVE (at NVD; CERT, LWN, oss-sec, fulldisc, Red Hat, Ubuntu, Gentoo, SUSE bugzilla/CVE, GitHub advisories/code/issues, web search, more)
References	DLA-2606-1, DSA-4880-1, ELA-390-1
Debian Bugs	985643

Vulnerable and fixed packages

The table below lists information on source packages.

Source Package	Release	Version	Status
lxml (PTS)	jessie, jessie (lts)	3.4.0-1+deb8u5	fixed
	stretch (security), stretch (lts), stretch	3.7.1-1+deb9u5	fixed
	buster (security), buster, buster (lts)	4.3.2-1+deb10u4	fixed
	bullseye (security), bullseye	4.6.3+dfsg-0.1+deb11u1	fixed
	bookworm	4.9.2-1	fixed
	sid, trixie	5.3.0-1	fixed

The information below is based on the following data on fixed versions.

Package	Type	Release	Fixed Version	Origin	Debian Bugs
lxml	source	jessie	3.4.0-1+deb8u4	ELA-390-1
lxml	source	stretch	3.7.1-1+deb9u4	DLA-2606-1
lxml	source	buster	4.3.2-1+deb10u3	DSA-4880-1
lxml	source	(unstable)	4.6.3-1		985643

Notes

https://bugs.launchpad.net/lxml/+bug/1888153
https://github.com/lxml/lxml/pull/316
https://github.com/lxml/lxml/commit/2d01a1ba8984e0483ce6619b972832377f208a0d