USN-4966-2: libx11 vulnerability

USN-4966-2: libx11 vulnerability

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.
Source: USN-4966-2: libx11 vulnerability