CVE-2026-44897: Mistune Project Mistune

Medium severity, CVSS 6.1. EPSS: 0.3% chance of exploitation in the next 30 days.

Mistune is a Python Markdown parser with renderers and plugins. Prior to 3.2.1, HTMLRenderer.heading() builds the opening <hN> tag by string-concatenating the id attribute value directly into the HTML — with no call to escape(), safe_entity(), or any other sanitisation function. A double-quote character " in the id value terminates the attribute, allowing an attacker to inject arbitrary additional attributes (event handlers, src=, href=, etc.) into the heading element. This vulnerability is fixed in 3.2.1.

Affected products

• Mistune Project Mistune: before 3.2.1 (fixed in 3.2.1)

Published 2026-05-26. Last modified 2026-07-24.