CVE-2026-59926

Summary

Mistune: XSS via unescaped class option in Admonition directive

Severity

medium

EPSS

0.3% (p26)

CWE

CWE-79

Also known as

GHSA-g97x-gvcm-x72h

Published

2026-07-20

Updated

2026-07-20

Advisory details

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.

References

• https://github.com/advisories/GHSA-g97x-gvcm-x72h
• https://github.com/lepture/mistune/security/advisories/GHSA-g97x-gvcm-x72h
• https://nvd.nist.gov/vuln/detail/CVE-2026-59926
• https://github.com/lepture/mistune/commit/a3cb6e5655308797e8be021d6c7b5bab13cbace2
• https://github.com/lepture/mistune/releases/tag/v3.2.1
• https://github.com/pypa/advisory-database/tree/main/vulns/mistune/PYSEC-2026-2214.yaml

Related advisories

• CVE-2026-59929 — medium · PyPI/mistune
• CVE-2026-59923 — medium · PyPI/mistune
• CVE-2026-115355 — high · PyPI/mistune
• GHSA-8cqv-vvq2-6p8c — high · PyPI/mistune
• CVE-2026-76098 — high · PyPI/mistune
• CVE-2026-59922 — high · PyPI/mistune
• CVE-2026-59925 — high · PyPI/mistune
• CVE-2026-59928 — high · PyPI/mistune

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