CVE-2026-71478: Thephpleague Commonmark

Medium severity, CVSS 6.1. EPSS: 0.4% chance of exploitation in the next 30 days.

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.

Affected products

• Thephpleague Commonmark: from 1.5.0, up to and including 2.8.3

Published 2026-08-06. Last modified 2026-09-10.