CVE-2026-44898
Description
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.
How to fix
- mistune_project mistune3.2.1 or later
- mistune3.2.1 or later
Affected products
| Product | Affected versions | Fixed in |
|---|---|---|
| mistune_project mistune | v < 3.2.1 | 3.2.1 |
| mistunePyPI | 3.2.0 ≤ v < 3.2.1, v < 3.2.1 | 3.2.1 |
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