CVE-2026-44897

Description

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.

Weakness classification

• security-advisories@github.com: CWE-79

Primary references

• security-advisories@github.com — Product, Release Notes
• security-advisories@github.com — Exploit, Vendor Advisory