CVE-2026-71478
league/commonmark is a PHP library for parsing and rendering CommonMark Markdown. From 1.5.0 until 2.9.0, the AttributesExtension's href and src unsafe-link filter can be bypassed by embedding control bytes, such as a tab, carriage return, line feed, or leading C0 control character, in a javascript: URL that browsers discard before parsing the scheme, causing the browser to still execute the script even when the unsafe-link filter is enabled. This issue is fixed in 2.9.0.
Weakness
league/commonmark is a PHP library for parsing and rendering CommonMark Markdown. From 1.5.0 until 2.9.0, the AttributesExtension's href and src unsafe-link filter can be bypassed by embedding control bytes, such as a tab, carriage return, line feed, or leading C0 control character, in a javascript: URL that browsers discard before parsing the scheme, causing the browser to still execute the script even when the unsafe-link filter is enabled. This issue is fixed in 2.9.0.
References
- https://github.com/thephpleague/commonmark/commit/493a5aa7d65754b73846006eaff9c2c4431a8e2c
- https://github.com/thephpleague/commonmark/releases/tag/2.9.0
- https://github.com/thephpleague/commonmark/security/advisories/GHSA-29pj-957v-52mc
- https://github.com/thephpleague/commonmark/security/advisories/GHSA-29pj-957v-52mc
Find the bug before an attacker does.
Sign in with GitHub and run your first audit in under a minute. The free plan needs no credit card.