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Advisories

justhtml before 1.14.0 Mutation XSS via custom sanitization policies

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severity
medium
date
Affecting

  • justhtml >= 0, < 1.14.0

CWE
  • CWE-79 Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
CVSS
5.1
CVSS V4 Vector
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:A/VC:N/VI:N/VA:N/SC:L/SI:L/SA:N
Credit
EmilStenstrom
Description
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.

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