A X.Org X Server security update has been released for Ubuntu 16.04 LTS, 18.04 LTS, 20.04 LTS, and 20.10.

==========================================================================
Ubuntu Security Notice USN-4656-1
December 01, 2020

xorg-server, xorg-server-hwe-16.04, xorg-server-hwe-18.04 vulnerabilities
==========================================================================

A security issue affects these releases of Ubuntu and its derivatives:

- Ubuntu 20.10
- Ubuntu 20.04 LTS
- Ubuntu 18.04 LTS
- Ubuntu 16.04 LTS

Summary:

Several security issues were fixed in X.Org X Server.

Software Description:
- xorg-server: X.Org X11 server
- xorg-server-hwe-18.04: X.Org X11 server
- xorg-server-hwe-16.04: X.Org X11 server

Details:

Jan-Niklas Sohn discovered that the X.Org X Server XKB extension
incorrectly handled certain inputs. A local attacker could possibly use
this issue to escalate privileges.

Update instructions:

The problem can be corrected by updating your system to the following
package versions:

Ubuntu 20.10:
xserver-xorg-core 2:1.20.9-2ubuntu1.1

Ubuntu 20.04 LTS:
xserver-xorg-core 2:1.20.8-2ubuntu2.6

Ubuntu 18.04 LTS:
xserver-xorg-core 2:1.19.6-1ubuntu4.8
xserver-xorg-core-hwe-18.04 2:1.20.8-2ubuntu2.2~18.04.4

Ubuntu 16.04 LTS:
xserver-xorg-core 2:1.18.4-0ubuntu0.11
xserver-xorg-core-hwe-16.04 2:1.19.6-1ubuntu4.1~16.04.5

After a standard system update you need to reboot your computer to make all
the necessary changes.

References:
  https://usn.ubuntu.com/4656-1
CVE-2020-14360, CVE-2020-25712

Package Information:
  https://launchpad.net/ubuntu/+source/xorg-server/2:1.20.9-2ubuntu1.1
  https://launchpad.net/ubuntu/+source/xorg-server/2:1.20.8-2ubuntu2.6
  https://launchpad.net/ubuntu/+source/xorg-server/2:1.19.6-1ubuntu4.8

  https://launchpad.net/ubuntu/+source/xorg-server-hwe-18.04/2:1.20.8-2ubuntu2.2~18.04.4
  https://launchpad.net/ubuntu/+source/xorg-server/2:1.18.4-0ubuntu0.11

  https://launchpad.net/ubuntu/+source/xorg-server-hwe-16.04/2:1.19.6-1ubuntu4.1~16.04.5