CVE-2025-46734

Date: May 5, 2025

league/commonmark is a PHP Markdown parser. A cross-site scripting (XSS) vulnerability in the Attributes extension of the league/commonmark library (versions 1.5.0 through 2.6.x) allows remote attackers to insert malicious JavaScript calls into HTML. The league/commonmark library provides configuration options such as "html_input: 'strip'" and "allow_unsafe_links: false" to mitigate cross-site scripting (XSS) attacks by stripping raw HTML and disallowing unsafe links. However, when the Attributes Extension is enabled, it introduces a way for users to inject arbitrary HTML attributes into elements via Markdown syntax using curly braces. Version 2.7.0 contains three changes to prevent this XSS attack vector: All attributes starting with "on" are considered unsafe and blocked by default; support for an explicit allowlist of allowed HTML attributes; and manually-added "href" and "src" attributes now respect the existing "allow_unsafe_links" configuration option. If upgrading is not feasible, please consider disabling the "AttributesExtension" for untrusted users and/or filtering the rendered HTML through a library like HTMLPurifier.