lepture/mistune · Security
Mistune: XSS via unescaped class option in Admonition directive
- GHSA ID
- GHSA-g97x-gvcm-x72h
- CVE ID
- CVE-2026-59926
- Severity
- medium
- Published
- Updated
- CVSS v4
- 5.3 · 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
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.
CWEs
- CWE-79 · Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
References
- 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 ↗
- https://github.com/advisories/GHSA-g97x-gvcm-x72h ↗