CVE-2026-5751
justhtml before 1.14.0 Mutation XSS via custom sanitization policies
CVSS Score
6.1
EPSS Score
0.0%
EPSS Percentile
0th
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.
| CWE | CWE-79 |
| Vendor | emilstenstrom |
| Product | justhtml |
| Published | Aug 23, 2026 |
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CVSS v3 Breakdown
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
Required
Scope
Changed
Confidentiality
Low
Integrity
Low
Availability
None
Affected Versions
EmilStenstrom / justhtml
0 < 1.14.0
References
Credits
EmilStenstrom