A libXdmcp security update has been released for Ubuntu Linux 14.04 ESM and 16.04 ESM.

USN-5690-1: libXdmcp vulnerability

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Ubuntu Security Notice USN-5690-1
October 19, 2022

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

- Ubuntu 16.04 ESM
- Ubuntu 14.04 ESM

Summary:

libXdmcp could be made to expose sensitive information.

Software Description:
- libxdmcp: X11 authorisation library (development headers)

Details:

It was discovered that libXdmcp was generating weak session keys.
A local attacker could possibly use this issue to perform a brute
force attack and obtain another user's key.

Update instructions:

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

Ubuntu 16.04 ESM:
libxdmcp6 1:1.1.2-1.1ubuntu0.1~esm1

Ubuntu 14.04 ESM:
libxdmcp6 1:1.1.1-1ubuntu0.1~esm1

In general, a standard system update will make all the necessary changes.

References:
https://ubuntu.com/security/notices/USN-5690-1
CVE-2017-2625