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.
History

Tue, 26 May 2026 23:00:00 +0000

Type Values Removed Values Added
First Time appeared Lepture
Lepture mistune
Vendors & Products Lepture
Lepture mistune

Tue, 26 May 2026 21:15:00 +0000

Type Values Removed Values Added
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.
Title Mistune TOC Anchor Injection XSS
Weaknesses CWE-79
References
Metrics cvssV3_1

{'score': 6.1, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N'}


cve-icon MITRE

Status: PUBLISHED

Assigner: GitHub_M

Published: 2026-05-26T20:41:53.805Z

Updated: 2026-05-26T20:41:53.805Z

Reserved: 2026-05-07T21:50:33.546Z

Link: CVE-2026-44898

cve-icon Vulnrichment

No data.

cve-icon NVD

Status : Received

Published: 2026-05-26T21:16:39.810

Modified: 2026-05-26T21:16:39.810

Link: CVE-2026-44898

cve-icon Redhat

No data.