Mistune Markdown Parser Attribute Injection and XSS Vulnerability

Publication date: 2026-05-26

Last updated on: 2026-06-09

Assigner: GitHub, Inc.

Description

Mistune is a Python Markdown parser with renderers and plugins. In 3.2.0 and earlier, in src/mistune/directives/image.py, the render_figure() function concatenates figclass and figwidth options directly into HTML attributes without escaping. This allows attribute injection and XSS even when HTMLRenderer(escape=True) is used, because these values bypass the inline renderer. Version 3.2.1 contains a patch.

CVSS Scores

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Meta Information

Published

2026-05-26

Last Modified

2026-06-09

Generated

2026-07-06

AI Q&A

2026-05-27

EPSS Evaluated

2026-07-04

NVD

CVE-2026-44896

Affected Vendors & Products

Vendor	Product	Version / Range
mistune_project	mistune	to 3.2.0 (inc)

Helpful Resources

Exploitability

CWE

KEV

CWE ID	Description
CWE-79	The product does not neutralize or incorrectly neutralizes user-controllable input before it is placed in output that is used as a web page that is served to other users.

Attack-Flow Graph

Executive Summary

This vulnerability exists in Mistune, a Python Markdown parser. In versions 3.2.0 and earlier, the render_figure() function in the image.py file concatenates the figclass and figwidth options directly into HTML attributes without escaping them. This improper handling allows an attacker to inject malicious attributes, leading to Cross-Site Scripting (XSS) attacks, even when the HTMLRenderer is set to escape HTML content.

Impact Analysis

The vulnerability can lead to attribute injection and Cross-Site Scripting (XSS) attacks. This means that an attacker could inject malicious scripts into web pages rendered by Mistune, potentially compromising the security of users by executing unauthorized scripts in their browsers. This can result in data theft, session hijacking, or other malicious activities.

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