Vulnerability Description
justhtml before 1.17.0 contains multiple security issues in sanitization, serialization, and programmatic DOM handling. When custom policies preserve foreign namespaces (SVG/MathML), dangerous content such as HTML integration points (SVG <foreignObject>, MathML <annotation-xml encoding="text/html">) and mutation-XSS parser-differential payloads could survive sanitization and become active HTML after reparse; SVG filter="url(...)" and preserved <style> could leave resource-loading CSS (@import, background-image:url()). Programmatic script/style/Comment nodes could serialize into active markup. Additional hardening fixes address sanitize-pipeline cache mutation and DOM parent/child cycles that could cause infinite loops. Most issues affect advanced or custom configurations rather than the default JustHTML(..., sanitize=True) safe path.
CVSS Score
MEDIUM
Related Weaknesses (CWE)
References
- https://github.com/EmilStenstrom/justhtml/security/advisories/GHSA-vrx2-77f2-ww3
- https://www.vulncheck.com/advisories/justhtml-before-multiple-cross-site-scripti
FAQ
What is CVE-2026-6827?
CVE-2026-6827 is a vulnerability with a CVSS score of 6.1 (MEDIUM). justhtml before 1.17.0 contains multiple security issues in sanitization, serialization, and programmatic DOM handling. When custom policies preserve foreign namespaces (SVG/MathML), dangerous content...
How severe is CVE-2026-6827?
CVE-2026-6827 has been rated MEDIUM with a CVSS base score of 6.1/10. Review the CVSS metrics above for detailed severity breakdown.
Is there a patch for CVE-2026-6827?
Check the references section above for vendor advisories and patch information. Review vendor security bulletins for remediation guidance.