{"id":"CVE-2026-5751","summary":"justhtml before 1.14.0 Mutation XSS via custom sanitization policies","details":"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 \u003cstyle\u003e). 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.","aliases":["GHSA-r758-8hxw-4845"],"modified":"2026-08-28T11:31:01.176990271Z","published":"2026-08-23T13:34:10.547Z","database_specific":{"cwe_ids":["CWE-79"],"osv_generated_from":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/5xxx/CVE-2026-5751.json","cna_assigner":"VulnCheck"},"references":[{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/5xxx/CVE-2026-5751.json"},{"type":"ADVISORY","url":"https://github.com/EmilStenstrom/justhtml/security/advisories/GHSA-r758-8hxw-4845"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-5751"},{"type":"ADVISORY","url":"https://www.vulncheck.com/advisories/justhtml-before-mutation-xss-via-custom-sanitization-policies"}],"affected":[{"ranges":[{"type":"GIT","repo":"https://github.com/emilstenstrom/justhtml","events":[{"introduced":"0"},{"fixed":"27f56428852decc3ca08b437f1cc9e0555384496"}],"database_specific":{"extracted_events":[{"introduced":"0"},{"fixed":"1.14.0"}],"source":"AFFECTED_FIELD"}}],"versions":["v1.13.0","v1.12.0","v1.11.0","v1.10.0","v1.9.1","v1.9.0","v1.8.0","v1.7.0","v1.6.0","v1.5.0","v1.4.0","v1.3.0","v1.2.0","v1.1.0","v1.0.0","v0.40.0","v0.39.0","v0.38.0","v0.37.0","v0.36.0","v0.35.0","v0.34.0","v0.33.0","v0.32.0","v0.31.0","v0.30.0","v0.29.0","v0.28.0","v0.27.0","v0.26.0","v0.25.0","v0.24.0","v0.23.0","v0.22.0","v0.21.0","v0.20.0","v0.19.0","v0.18.0","v0.17.0","v0.16.0","v0.15.0","v0.14.0","v0.13.1","v0.13.0","v0.12.0","v0.11.0","v0.10.0","v0.9.0","v0.8.0","v0.7.0","v0.6.0","v0.5.2","v0.5.1","v0.5.0","v0.4.0","v0.3.0","v0.2.0","v0.1.0"],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-5751.json"}}],"schema_version":"1.9.0","severity":[{"type":"CVSS_V4","score":"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"}]}