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[USN-8194-1] league/commonmark vulnerabilities

Posted on 23 April 2026
Ubuntu Security

==========================================================================Ubuntu Security Notice USN-8194-1
April 21, 2026

php-league-commonmark vulnerabilities
==========================================================================
A security issue affects these releases of Ubuntu and its derivatives:

- Ubuntu 24.04 LTS
- Ubuntu 22.04 LTS
- Ubuntu 20.04 LTS

Summary:

Several security issues were fixed in league/commonmark.

Software Description:
- php-league-commonmark: Highly-extensible PHP Markdown parser which fully supports the CommonMark and GFM specs

Details:

It was discovered that league/commonmark did not properly restrict
unsafe attributes when the Attributes extension was enabled. An attacker
could possibly use this issue to cause cross-site scripting by injecting
malicious code into rendered HTML. This issue only affected Ubuntu 22.04
LTS and Ubuntu 24.04 LTS. (CVE-2025-46734)

It was discovered that league/commonmark did not properly block certain
disallowed HTML tags in some cases. An attacker could possibly use this
issue to cause cross-site scripting by inserting malicious HTML that
bypassed filtering. (CVE-2026-30838)

It was discovered that league/commonmark did not properly enforce domain
allowlist checks in the Embed extension. An attacker could possibly use
this issue to bypass domain restrictions and cause untrusted content to
be treated as allowed. This issue only affected Ubuntu 24.04 LTS.
(CVE-2026-33347)

Update instructions:

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

Ubuntu 24.04 LTS
php-league-commonmark 2.4.2-2ubuntu0.1~esm1
Available with Ubuntu Pro

Ubuntu 22.04 LTS
php-league-commonmark 1.6.7-1ubuntu0.1~esm1
Available with Ubuntu Pro

Ubuntu 20.04 LTS
php-league-commonmark 1.3.1-1ubuntu2+esm1
Available with Ubuntu Pro

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

References:
https://ubuntu.com/security/notices/USN-8194-1
CVE-2025-46734, CVE-2026-30838, CVE-2026-33347

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