Ubuntu Security Notice USN-4966-2
May 25, 2021

libx11 vulnerability

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

- Ubuntu 16.04 ESM
- Ubuntu 14.04 ESM


libx11 could allow unintended access to services.

Software Description:
- libx11: X11 client-side library


USN-4966-1 fixed a vulnerability in libx11. This update provides
the corresponding update for Ubuntu 14.04 ESM and Ubuntu 16.04 ESM.

Original advisory details:

 It was discovered that libx11 incorrectly validated certain parameter
 lengths. A remote attacker could possibly use this issue to trick libx11
 into emitting extra X protocol requests.

Update instructions:

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

Ubuntu 16.04 ESM:
  libx11-6                        2:1.6.3-1ubuntu2.2+esm1

Ubuntu 14.04 ESM:
  libx11-6                        2:1.6.2-1ubuntu2.1+esm2

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