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[USN-8913-1] libx11 vulnerabilities

Posted on 12 October 2026
Ubuntu Security

==========================================================================Ubuntu Security Notice USN-8913-1
October 12, 2026

libx11 vulnerabilities
==========================================================================
A security issue affects these releases of Ubuntu and its derivatives:

- Ubuntu 26.04 LTS
- Ubuntu 24.04 LTS
- Ubuntu 22.04 LTS
- Ubuntu 20.04 LTS
- Ubuntu 18.04 LTS
- Ubuntu 16.04 LTS
- Ubuntu 14.04 LTS

Summary:

Several security issues were fixed in libx11.

Software Description:
- libx11: X11 client-side library

Details:

Adam Bedard discovered that libx11 incorrectly handled certain XKB keyboard
map replies. If a user were tricked into connecting to a malicious X
server, a remote attacker could possibly use this issue to cause libx11 to
crash, resulting in a denial of service, or possibly execute arbitrary
code. (CVE-2026-88806)

It was discovered that libx11 incorrectly handled certain X Input Method
(XIM) messages. If a user were tricked into connecting to a malicious X
server, a remote attacker could possibly use these issues to cause libx11
to crash, resulting in a denial of service. (CVE-2026-94283,
CVE-2026-94284)

It was discovered that libx11 incorrectly handled converting certain
multibyte text. An attacker could possibly use this issue to cause libx11
to crash, resulting in a denial of service. (CVE-2026-94285)

Update instructions:

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

Ubuntu 26.04 LTS
libx11-6 2:1.8.13-1ubuntu0.1

Ubuntu 24.04 LTS
libx11-6 2:1.8.7-1ubuntu0.1

Ubuntu 22.04 LTS
libx11-6 2:1.7.5-1ubuntu0.4

Ubuntu 20.04 LTS
libx11-6 2:1.6.9-2ubuntu1.6+esm1
Available with Ubuntu Pro

Ubuntu 18.04 LTS
libx11-6 2:1.6.4-3ubuntu0.4+esm3
Available with Ubuntu Pro

Ubuntu 16.04 LTS
libx11-6 2:1.6.3-1ubuntu2.2+esm5
Available with Ubuntu Pro

Ubuntu 14.04 LTS
libx11-6 2:1.6.2-1ubuntu2.1+esm6
Available with Ubuntu Pro

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

References:
https://ubuntu.com/security/notices/USN-8913-1
CVE-2026-88806, CVE-2026-94283, CVE-2026-94284, CVE-2026-94285

Package Information:
https://launchpad.net/ubuntu/+source/libx11/2:1.8.13-1ubuntu0.1
https://launchpad.net/ubuntu/+source/libx11/2:1.8.7-1ubuntu0.1
https://launchpad.net/ubuntu/+source/libx11/2:1.7.5-1ubuntu0.4

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