GitHub Advisoryadvisory · PyPI

GHSA-g97x-gvcm-x72h Mistune: XSS via unescaped class option in Admonition directive

MEDIUM Published 2026-07-20 Modified 2026-07-20 Official page ↗
Aliases
CVE-2026-59926
Ecosystem
PyPI
Packages
mistune
Severity
Moderate
CVSS vector
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:L/VI:L/VA:N/SC:L/SI:L/SA:N
Weaknesses
CWE-79
Reviewed
2026-07-20

Affected packages

• PyPI mistune: < 3.3.0 → fixed in 3.3.0

Description

In `src/mistune/directives/admonition.py`, the `render_admonition()` function concatenates the `:class:` option directly into the HTML class attribute without escaping (lines 63-68). This allows attribute injection and XSS even when `HTMLRenderer(escape=True)` is used. The directive name parameter is safe (validated against whitelist), but the class option comes from raw user input.

Related

Alias · CVE (1)

  • CVE-2026-59926 Mistune is a Python Markdown parser with renderers and plugins. vulnerability

Weakness · CWE (1)

  • CWE-79 Improper Neutralization of Input During Web Page Generation weakness

References