A xorg-server security update has been released for Debian GNU/Linux 10 and 11 to address multiple input validation failures.

DSA 5027-1: xorg-server security update

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Debian Security Advisory DSA-5027-1 security@debian.org
  https://www.debian.org/security/ Salvatore Bonaccorso
December 21, 2021   https://www.debian.org/security/faq
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Package : xorg-server
CVE ID : CVE-2021-4008 CVE-2021-4009 CVE-2021-4010 CVE-2021-4011

Jan-Niklas Sohn discovered that multiple input validation failures in X
server extensions of the X.org X server may result in privilege
escalation if the X server is running privileged.

For the oldstable distribution (buster), these problems have been fixed
in version 2:1.20.4-1+deb10u4.

For the stable distribution (bullseye), these problems have been fixed in
version 2:1.20.11-1+deb11u1.

We recommend that you upgrade your xorg-server packages.

For the detailed security status of xorg-server please refer to its
security tracker page at:
  https://security-tracker.debian.org/tracker/xorg-server

Further information about Debian Security Advisories, how to apply
these updates to your system and frequently asked questions can be
found at:   https://www.debian.org/security/