CVE-2026-44898

CVE-2026-44898 · Mistune TOC Anchor Injection XSS

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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.

CVSS 6.1 · Medium · EPSS 0.3% · Fix available

Published

2026-05-26T20:41:53.805Z

Updated

2026-05-27T17:57:38.643Z

Stack: system · python

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