CVE-2026-44896: Mistune: XSS via unescaped figclass/figwidth in Figure directive

Severity: medium (CVSS 6.1 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.2% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-05-26 · updated 2026-07-24
Weakness: CWE-79

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.

Affected products

lepture mistune: through 3.2.0

References

https://github.com/lepture/mistune/commit/a3cb6e5655308797e8be021d6c7b5bab13cbace2
https://github.com/lepture/mistune/security/advisories/GHSA-58cw-g322-p94v

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