CVE-2026-44898 PUBLISHED

Mistune is a Python Markdown parser with renderers and plugins. Prior to 3.2.1, render_toc_ul() builds a

table-of-contents tree from a list of (level, id, text) tuples. Both the id value (used as href="#<id>") and the text value (used as the visible link label) are inserted into tags via a plain Python format string — with no HTML escaping applied to either value. When heading IDs are derived from user-supplied heading text (the standard use-case for readable slug anchors), an attacker can craft a heading whose text breaks out of the href="#..." attribute context, injecting arbitrary HTML tags including <script> blocks directly into the rendered TOC. This vulnerability is fixed in 3.2.1.

• https://github.com/lepture/mistune/security/advisories/GHSA-6269-cqxg-mhhv
• https://github.com/lepture/mistune/releases/tag/v3.2.1

• CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting') CWE