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

May 8, 2026

In src/mistune/directives/image.py, the render_figure() function concatenates figclass and figwidth options directly into HTML attributes without escaping (lines 152-168).

This allows attribute injection and XSS even when HTMLRenderer(escape=True) is used, because these values bypass the inline renderer.

Other attributes in the same file (src, alt, style) are properly escaped; figclass/figwidth were missed.

References

github.com/advisories/GHSA-58cw-g322-p94v
github.com/lepture/mistune
github.com/lepture/mistune/security/advisories/GHSA-58cw-g322-p94v
nvd.nist.gov/vuln/detail/CVE-2026-44896

Code Behaviors & Features

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