=========================================================================Ubuntu Security Notice USN-4905-1
April 13, 2021

xorg-server, xorg-server-hwe-16.04, xorg-server-hwe-18.04 vulnerability
=========================================================================
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:

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
- 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 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 20.10:
  xserver-xorg-core               2:1.20.9-2ubuntu1.3

Ubuntu 20.04 LTS:
  xserver-xorg-core               2:1.20.9-2ubuntu1.2~20.04.2

Ubuntu 18.04 LTS:
  xserver-xorg-core               2:1.19.6-1ubuntu4.9
  xserver-xorg-core-hwe-18.04     2:1.20.8-2ubuntu2.2~18.04.5

Ubuntu 16.04 LTS:
  xserver-xorg-core               2:1.18.4-0ubuntu0.12
  xserver-xorg-core-hwe-16.04     2:1.19.6-1ubuntu4.1~16.04.6

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

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

Package Information:
  https://launchpad.net/ubuntu/+source/xorg-server/2:1.20.9-2ubuntu1.3
  https://launchpad.net/ubuntu/+source/xorg-server/2:1.20.9-2ubuntu1.2~20.04.2
  https://launchpad.net/ubuntu/+source/xorg-server/2:1.19.6-1ubuntu4.9

https://launchpad.net/ubuntu/+source/xorg-server-hwe-18.04/2:1.20.8-2ubuntu2.2~18.04.5
  https://launchpad.net/ubuntu/+source/xorg-server/2:1.18.4-0ubuntu0.12

https://launchpad.net/ubuntu/+source/xorg-server-hwe-16.04/2:1.19.6-1ubuntu4.1~16.04.6