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[USN-8939-1] libXtst vulnerabilities

Posted on 19 October 2026
Ubuntu Security

==========================================================================Ubuntu Security Notice USN-8939-1
October 19, 2026

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

- Ubuntu 26.10
- Ubuntu 26.04 LTS
- Ubuntu 24.04 LTS
- Ubuntu 22.04 LTS
- Ubuntu 20.04 LTS
- Ubuntu 18.04 LTS
- Ubuntu 16.04 LTS

Summary:

Several security issues were fixed in libXtst.

Software Description:
- libxtst: X11 Record extension library

Details:

It was discovered that libXtst did not properly handle certain RECORD
replies from the X server. A malicious X server could possibly use this
issue to cause libXtst clients to crash, resulting in a denial of service.
(CVE-2026-94286)

Tobias Stoeckmann discovered that libXtst did not properly handle certain
memory operations. A malicious X server could possibly use this issue to
cause libXtst to access memory out of bounds, resulting in a denial of
service. This issue only affected Ubuntu 16.04 LTS. (CVE-2016-7951)

Tobias Stoeckmann discovered that libXtst did not properly handle certain
replies from the X server. A malicious X server could possibly use this
issue to cause libXtst to enter an infinite loop, resulting in a denial of
service. This issue only affected Ubuntu 16.04 LTS. (CVE-2016-7952)

Update instructions:

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

Ubuntu 26.10
libxtst-dev 2:1.2.5-1ubuntu1
libxtst6 2:1.2.5-1ubuntu1

Ubuntu 26.04 LTS
libxtst-dev 2:1.2.5-1ubuntu0.1
libxtst6 2:1.2.5-1ubuntu0.1

Ubuntu 24.04 LTS
libxtst-dev 2:1.2.3-1.1ubuntu0.1
libxtst6 2:1.2.3-1.1ubuntu0.1

Ubuntu 22.04 LTS
libxtst-dev 2:1.2.3-1ubuntu0.22.04.1
libxtst6 2:1.2.3-1ubuntu0.22.04.1

Ubuntu 20.04 LTS
libxtst-dev 2:1.2.3-1ubuntu0.20.04.1~esm1
Available with Ubuntu Pro
libxtst6 2:1.2.3-1ubuntu0.20.04.1~esm1
Available with Ubuntu Pro

Ubuntu 18.04 LTS
libxtst-dev 2:1.2.3-1ubuntu0.18.04.1~esm1
Available with Ubuntu Pro
libxtst6 2:1.2.3-1ubuntu0.18.04.1~esm1
Available with Ubuntu Pro

Ubuntu 16.04 LTS
libxtst-dev 2:1.2.2-1ubuntu0.1~esm1
Available with Ubuntu Pro
libxtst6 2:1.2.2-1ubuntu0.1~esm1
Available with Ubuntu Pro

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

References:
https://ubuntu.com/security/notices/USN-8939-1
CVE-2016-7951, CVE-2016-7952, CVE-2026-94286

Package Information:
https://launchpad.net/ubuntu/+source/libxtst/2:1.2.5-1ubuntu1
https://launchpad.net/ubuntu/+source/libxtst/2:1.2.5-1ubuntu0.1
https://launchpad.net/ubuntu/+source/libxtst/2:1.2.3-1.1ubuntu0.1
https://launchpad.net/ubuntu/+source/libxtst/2:1.2.3-1ubuntu0.22.04.1

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