CVE-2026-5751justhtml before 1.14.0 Mutation XSS via custom sanitization policies
Updated under an hour ago ()
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No exploitation reported and no EPSS estimate yet.
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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
- 6.1 MEDIUM (v3.1, CNA)CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
- Weakness (CWE)
- CWE-79
- Known exploited
- Not in CISA's KEV catalog
- EPSS (exploitation in the next 30 days)
- Not loaded for this CVE
- Assigned by
- VulnCheck
- NVD analysis
- Deferred
- Record last updated
- Aug 24, 2026
- First seen by InfoSec Signals
- Oct 9, 2026
Affected products
EmilStenstrom justhtml emilstenstrom:justhtml (from the name) | before 1.14.0; 1.14.0 not affected | CNA record |
References
- https://github.com/EmilStenstrom/justhtml/security/advisories/GHSA-r758-8hxw-4845vendor-advisory
- https://www.vulncheck.com/advisories/justhtml-before-mutation-xss-via-custom-sanitization-policiesthird-party-advisory
The CVE record on cve.org NVD's entry
The CVE record is authoritative. Products marked “from the name” were identified from the CNA's free-text names, not a CPE, and are matched less certainly. This product uses the NVD API but is not endorsed or certified by the NVD.