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USN-4966-2: libx11 vulnerability

25 May 2021

libx11 could allow unintended access to services.



  • 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
Ubuntu 14.04

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


Related notices

  • USN-4966-1: libx11-6, libx11-6-udeb, libx11, libx11-xcb-dev, libx11-dev, libx11-doc, libx11-xcb1, libx11-data