CVE-2021-31535

Name	CVE-2021-31535
Description	LookupCol.c in X.Org X through X11R7.7 and libX11 before 1.7.1 might allow remote attackers to execute arbitrary code. The libX11 XLookupColor request (intended for server-side color lookup) contains a flaw allowing a client to send color-name requests with a name longer than the maximum size allowed by the protocol (and also longer than the maximum packet size for normal-sized packets). The user-controlled data exceeding the maximum size is then interpreted by the server as additional X protocol requests and executed, e.g., to disable X server authorization completely. For example, if the victim encounters malicious terminal control sequences for color codes, then the attacker may be able to take full control of the running graphical session.
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-2666-1, DSA-4920-1, ELA-433-1
Debian Bugs	988737

Vulnerable and fixed packages

The table below lists information on source packages.

Source Package	Release	Version	Status
libx11 (PTS)	jessie, jessie (lts)	2:1.6.2-3+deb8u7	fixed
	stretch (security)	2:1.6.4-3+deb9u4	fixed
	stretch (lts), stretch	2:1.6.4-3+deb9u6	fixed
	buster (security), buster, buster (lts)	2:1.6.7-1+deb10u4	fixed
	bullseye (security), bullseye	2:1.7.2-1+deb11u2	fixed
	bookworm (security), bookworm	2:1.8.4-2+deb12u2	fixed
	sid, trixie	2:1.8.10-2	fixed

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

Package	Type	Release	Fixed Version	Origin	Debian Bugs
libx11	source	jessie	2:1.6.2-3+deb8u5	ELA-433-1
libx11	source	stretch	2:1.6.4-3+deb9u4	DLA-2666-1
libx11	source	buster	2:1.6.7-1+deb10u2	DSA-4920-1
libx11	source	(unstable)	2:1.7.1-1		988737

Notes

https://gitlab.freedesktop.org/xorg/lib/libx11/-/commit/8d2e02ae650f00c4a53deb625211a0527126c605
https://www.openwall.com/lists/oss-security/2021/05/18/2
https://www.openwall.com/lists/oss-security/2021/05/18/3
https://unparalleled.eu/publications/2021/advisory-unpar-2021-1.txt
https://unparalleled.eu/blog/2021/20210518-using-xterm-to-navigate-the-huge-color-space/