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[USN-8815-1] libass vulnerabilities

Posted on 24 September 2026
Ubuntu Security

==========================================================================Ubuntu Security Notice USN-8815-1
September 24, 2026

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

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

Summary:

Several security issues were fixed in libass.

Software Description:
- libass: Portable subtitle renderer for the ASS/SSA subtitle format

Details:

It was discovered that libass incorrectly handled parsing operations for
specific nested character strings. An attacker could use this issue to
cause libass to crash, resulting in a denial of service, or possibly
execute arbitrary code. This issue only affected Ubuntu 14.04 LTS,
Ubuntu 16.04 LTS, Ubuntu 18.04 LTS and Ubuntu 20.04 LTS.
(CVE-2020-24994)

It was discovered that libass incorrectly handled certain outline
processing operations. An attacker could use this issue to cause libass
to crash, resulting in a denial of service. This issue only affected
Ubuntu 18.04 LTS and Ubuntu 20.04 LTS. (CVE-2020-26682)

It was discovered that libass incorrectly handled certain ASS subtitle
files when measuring wrapped lines. An attacker could use this issue to
cause libass to crash, resulting in a denial of service, or possibly
execute arbitrary code. This issue only affected Ubuntu 24.04 LTS and
Ubuntu 26.04 LTS. (CVE-2026-61627)

It was discovered that libass incorrectly handled certain Matroska
subtitle chunks with negative ReadOrder values. An attacker could use
this issue to cause libass to crash, resulting in a denial of service,
or possibly execute arbitrary code. This issue only affected Ubuntu
26.04 LTS. (CVE-2026-61626)

Update instructions:

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

Ubuntu 26.04 LTS
libass9 1:0.17.4-2ubuntu0.1~esm1
Available with Ubuntu Pro

Ubuntu 24.04 LTS
libass9 1:0.17.1-2ubuntu0.1~esm1
Available with Ubuntu Pro

Ubuntu 20.04 LTS
libass9 1:0.14.0-2ubuntu0.1~esm1
Available with Ubuntu Pro

Ubuntu 18.04 LTS
libass9 1:0.14.0-1ubuntu0.1~esm1
Available with Ubuntu Pro

Ubuntu 14.04 LTS
libass4 0.10.1-3ubuntu1+esm2
Available with Ubuntu Pro

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

References:
https://ubuntu.com/security/notices/USN-8815-1
CVE-2020-24994, CVE-2020-26682, CVE-2026-61626, CVE-2026-61627

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