A X.Org X Server security update has been released for Ubuntu Linux 14.04 ESM and 16.04 ESM.

USN-5193-2: X.Org X Server vulnerabilities

=========================================================================
Ubuntu Security Notice USN-5193-2
January 26, 2022

xorg-server vulnerabilities
=========================================================================
A security issue affects these releases of Ubuntu and its derivatives:

- Ubuntu 16.04 ESM
- Ubuntu 14.04 ESM

Summary:

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

Software Description:
- xorg-server: X.Org X11 server

Details:

USN-5193-1 fixed several vulnerabilities in X.Org. This update provides
the corresponding update for Ubuntu 14.04 ESM and Ubuntu 16.04 ESM.

Original advisory details:

Jan-Niklas Sohn discovered that the X.Org X Server incorrectly handled
certain inputs. An attacker could use this issue to cause the server to
crash, resulting in a denial of service, or possibly execute arbitrary
code and escalate privileges.

Update instructions:

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

Ubuntu 16.04 ESM:
xserver-xorg-core 2:1.18.4-0ubuntu0.12+esm1

Ubuntu 14.04 ESM:
xserver-xorg-core 2:1.15.1-0ubuntu2.11+esm5

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

References:
  https://ubuntu.com/security/notices/USN-5193-2
  https://ubuntu.com/security/notices/USN-5193-1
CVE-2021-4008, CVE-2021-4009, CVE-2021-4011