CVE-2026-5751

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 v3 6.1 MEDIUM

6.1^/10

CVSS v3 : MEDIUM

Vector :

Exploitability : 2.8 / Impact : 2.7

Attack Vector NETWORK

Attack Complexity LOW

Privileges Required NONE

User Interaction REQUIRED

Confidentiality Impact LOW

Integrity Impact LOW

Availability Impact NONE

Scope CHANGED

References

Link	Resource
https://github.com/EmilStenstrom/justhtml/security/advisories/GHSA-r758-8hxw-4845
https://www.vulncheck.com/advisories/justhtml-before-mutation-xss-via-custom-sanitization-policies

Configurations

No configuration.

History

No history.

Information

Published : 2026-08-23 14:16

Updated : 2026-08-26 17:10

NVD link : CVE-2026-5751

Mitre link : CVE-2026-5751

CVE.ORG link : CVE-2026-5751

JSON object : View

Products Affected

No product.

CWE

CWE-79

Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')

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