CVE-2026-44898

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

• CWE-79

• https://github.com/lepture/mistune/releases/tag/v3.2.1Product, Release Notes
• https://github.com/lepture/mistune/security/advisories/GHSA-6269-cqxg-mhhvExploit, Vendor Advisory
• https://github.com/lepture/mistune/security/advisories/GHSA-6269-cqxg-mhhvExploit, Vendor Advisory

Published

May 26, 2026

Last Modified

Jul 24, 2026

Status

Analyzed

• How Strix found a critical auth bypass in etcdStrix autonomously discovered a critical authentication bypass in etcd, later designated CVE-2026-33413.
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