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CVE-2026-5751

CVE-2026-5751 · justhtml before 1.14.0 Mutation XSS via custom sanitization policies

This page contains facts from public vulnerability sources. Check the original advisory before updating.

justhtml versions 1.13.0 and earlier contain a parser-differential / mutation cross-site scripting (mXSS) vulnerability when using a custom SanitizationPolicy that preserves foreign namespaces (e.g., drop_foreign_namespaces=False with allowlisted SVG/MathML elements or raw-text containers such as <style>). Specially crafted input can sanitize into markup that appears safe but becomes unsafe when re-parsed by a browser or another HTML parser, allowing markup injection. The default safe configuration (sanitize=True) is not affected. Fixed in 1.14.0.

CVSS 5.1 · Medium · EPSS 0.3% · Fix available

Published
Updated

Stack: python

Affected products and versions

  • justhtml

    Versions
    • ≥ 0, < 1.14.0: Affected (semver)
    • 1.14.0: Not affected (semver)

    Update to 1.14.0

  • justhtml PyPI

    Versions
    • 1.13.0
    Affected ranges
    • ECOSYSTEM: ≥ 1.13.0, < 1.14.0

    Update to 1.14.0

Original sources

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