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[USN-8872-1] libxmltok vulnerabilities

Posted on 06 October 2026
Ubuntu Security

==========================================================================Ubuntu Security Notice USN-8872-1
October 05, 2026

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

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

Summary:

libxmltok could be made to crash if it opened a specially crafted
file.

Software Description:
- libxmltok: XML Parser Toolkit, developer libraries

Details:

It was discovered that Expat, contained with the xmltok library did not
correctly handle certain integer arithmetic. If a user or automated
system were tricked into opening a specially crafted file, an attacker
could possibly cause a denial of service. (CVE-2026-56404, CVE-2026-56405)

Update instructions:

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

Ubuntu 24.04 LTS
libxmltok1-dev 1.2-4.1ubuntu2.24.0.4.1+esm5
Available with Ubuntu Pro
libxmltok1t64 1.2-4.1ubuntu2.24.0.4.1+esm5
Available with Ubuntu Pro

Ubuntu 22.04 LTS
libxmltok1 1.2-4ubuntu0.22.04.1~esm7
Available with Ubuntu Pro
libxmltok1-dev 1.2-4ubuntu0.22.04.1~esm7
Available with Ubuntu Pro

Ubuntu 20.04 LTS
libxmltok1 1.2-4ubuntu0.20.04.1~esm7
Available with Ubuntu Pro
libxmltok1-dev 1.2-4ubuntu0.20.04.1~esm7
Available with Ubuntu Pro

Ubuntu 18.04 LTS
libxmltok1 1.2-4ubuntu0.18.04.1~esm7
Available with Ubuntu Pro
libxmltok1-dev 1.2-4ubuntu0.18.04.1~esm7
Available with Ubuntu Pro

Ubuntu 16.04 LTS
libxmltok1 1.2-3ubuntu0.1~esm1
Available with Ubuntu Pro
libxmltok1-dev 1.2-3ubuntu0.1~esm1
Available with Ubuntu Pro

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

References:
https://ubuntu.com/security/notices/USN-8872-1
CVE-2026-56404, CVE-2026-56405

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