{"id":"CVE-2026-5751","title":"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 al…","summary":"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 al…","severity":"medium","cvss":6.1,"cvssVector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N","cwe":["CWE-79"],"vendor":"justhtml","product":"justhtml","affected":["justhtml >= 1.13.0, < 1.14.0"],"patched":["justhtml 1.14.0"],"published":"2026-08-23","updated":"2026-10-12","sourceUpdated":"2026-10-12T16:10:00.220","source":"NVD","sourceUrl":"https://nvd.nist.gov/vuln/detail/CVE-2026-5751","references":[{"url":"https://github.com/EmilStenstrom/justhtml/security/advisories/GHSA-r758-8hxw-4845","label":"disclosure@vulncheck.com"},{"url":"https://www.vulncheck.com/advisories/justhtml-before-mutation-xss-via-custom-sanitization-policies","label":"disclosure@vulncheck.com"},{"url":"https://github.com/EmilStenstrom/justhtml/commit/8adc4dfe31723dc522f44338f9bd98381c92b076"},{"url":"https://github.com/EmilStenstrom/justhtml"},{"url":"https://github.com/EmilStenstrom/justhtml/releases/tag/v1.14.0"}],"tags":["nvd","osv","pip"],"epss":0.00263,"epssPercentile":0.17997,"aliases":["GHSA-r758-8hxw-4845"],"ecosystem":"pip","ingestedAt":"2026-08-24T19:25:44.289Z","slug":"CVE-2026-5751","body":"## Overview\n\njusthtml 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.\n\n## Remediation\n\nRefer to the linked advisories for vendor-supplied fixes and affected version ranges.\n\n## Package advisory (CVE-2026-5751)\n\nAffected packages:\n\n- `justhtml >= 1.13.0, < 1.14.0`\n\nPatched in:\n\n- `justhtml 1.14.0`\n\nSource: https://osv.dev/vulnerability/GHSA-r758-8hxw-4845","depth":"sunlit","depthScore":34,"depthScoreParts":{"impact":33.6,"likelihood":0.1,"exploitation":0,"ransomware":0},"changes":[{"seq":219486,"id":"CVE-2026-5751","ts":1791824360337,"field":"cvss","old":null,"new":"6.1"},{"seq":219485,"id":"CVE-2026-5751","ts":1791824360337,"field":"severity","old":"low","new":"medium"}]}