Jan-Niklas Sohn discovered that a user-after-free flaw in the Composite extension of the X.org X server may result in privilege escalation if the X server is running under the root user.
For the stable distribution (bullseye), this problem has been fixed in version 2:1.20.11-1+deb11u6.
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