{"cve":"CVE-2026-5751","nvd":{"published":"2026-08-23T14:16:53.807","modified":"2026-10-12T16:10:00.220","status":"Deferred","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.","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","score":5.1},"cvss_v3":{"version":"3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N","score":6.1},"cwes":["CWE-79"],"references":["https://github.com/EmilStenstrom/justhtml/security/advisories/GHSA-r758-8hxw-4845","https://www.vulncheck.com/advisories/justhtml-before-mutation-xss-via-custom-sanitization-policies"],"products":[],"source":"nvd","synced_at":"2026-10-19T22:49:38.260478770+00:00"},"epss":{"cve":"CVE-2026-5751","score":0.00263,"percentile":0.1792,"date":"2026-10-25"},"kev":null,"osv":[{"id":"GHSA-r758-8hxw-4845","url":"https://osv.dev/vulnerability/GHSA-r758-8hxw-4845","summary":"justhtml: Mutation XSS with custom foreign-namespace sanitization policies","modified":"2026-08-24T03:55:59.795016825Z","packages":[{"ecosystem":"PyPI","name":"justhtml","purl":"pkg:pypi/justhtml","ranges":[">=1.13.0 <1.14.0"],"fixed":["1.14.0"]}]}],"attribution":["This product uses the NVD API but is not endorsed or certified by the NVD.","EPSS scores: FIRST Exploit Prediction Scoring System, https://www.first.org/epss","Known exploited vulnerabilities: CISA Known Exploited Vulnerabilities Catalog, https://www.cisa.gov/known-exploited-vulnerabilities-catalog","Package advisories: OSV (https://osv.dev), from the GitHub Advisory Database, PyPA, Go, RustSec and other ecosystem databases, under CC-BY 4.0 or CC0","CVE records: the CVE Program's CVE List (https://www.cve.org), under its terms of use (https://www.cve.org/Legal/TermsOfUse). CVE is a registered trademark of The MITRE Corporation; this product is not affiliated with the CVE Program."]}