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

USN-4905-2: X.Org X Server vulnerability

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Ubuntu Security Notice USN-4905-2
June 30, 2021

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

- Ubuntu 14.04 ESM

Summary:

X.Org X Server could be made to crash or run programs if it received
specially crafted input.

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

Details:

USN-4905-1 fixed a vulnerability in X.Org. This update provides
the corresponding update for Ubuntu 14.04 ESM.

Original advisory details:

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

Update instructions:

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

Ubuntu 14.04 ESM:
xserver-xorg-core 2:1.15.1-0ubuntu2.11+esm4

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

References:
  https://ubuntu.com/security/notices/USN-4905-2
  https://ubuntu.com/security/notices/USN-4905-1
CVE-2021-3472