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.
Affected products
mistune_project: mistune
References3
- github.com/lepture/mistune/security/advisories/GHSA-6269-cqxg-m… ExploitVendor Advisory
- github.com/lepture/mistune/security/advisories/GHSA-6269-cqxg-m… ExploitVendor Advisory
- github.com/lepture/mistune/releases/tag/v3.2.1 ProductRelease Notes
Metrics
- CVSS 3.1
-
6.1
MEDIUM
Score source: CNA
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N - EPSS — exploit probability
- 0% percentile: 14 · as of 14 November 2026
- CWE
- CWE-79
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