USN-8194-1: league/commonmark vulnerabilities

USN-8194-1: league/commonmark vulnerabilities

Publication date: 21 April 2026
Overview: Several security issues were fixed in league/commonmark

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

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

• 24.04 LTS noble php-league-commonmark – 2.4.2-2ubuntu0.1~esm1
• 22.04 LTS jammy php-league-commonmark – 1.6.7-1ubuntu0.1~esm1
• 20.04 LTS focal php-league-commonmark – 1.3.1-1ubuntu2+esm1