NuytsTech Security

CVE-2026-44898

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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=”#“) 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