{"id":"UBUNTU-CVE-2026-86431","details":"league/commonmark (thephpleague/commonmark) versions \u003e= 2.7.0 and \u003c 2.9.1 contain a cross-site scripting vulnerability in the AttributesExtension. Prefixing an attribute name with a single U+000C form feed byte (e.g. {\\x0Conclick=\"alert(1)\"}) bypasses the AttributesHelper::filterAttributes() 'on*' event-handler filter because PHP's trim() does not strip U+000C, causing the attribute to be written verbatim into the output where browsers parse it as a genuine event handler. The same prefix also defeats the allow_unsafe_links check, allowing javascript: URIs through href/src attributes even when allow_unsafe_links is false. Exploitation requires processing untrusted Markdown with the AttributesExtension enabled; the injected script executes when the rendered HTML is viewed. Fixed in 2.9.1.","modified":"2026-09-16T14:02:38.804943335Z","published":"2026-09-07T13:20:00Z","upstream":["CVE-2026-86431"],"references":[{"type":"REPORT","url":"https://ubuntu.com/security/CVE-2026-86431"},{"type":"REPORT","url":"https://www.cve.org/CVERecord?id=CVE-2026-86431"},{"type":"REPORT","url":"https://github.com/thephpleague/commonmark/security/advisories/GHSA-f8fg-pg57-v4j8"}],"affected":[{"package":{"name":"php-league-commonmark","ecosystem":"Ubuntu:Pro:20.04:LTS","purl":"pkg:deb/ubuntu/php-league-commonmark?arch=source&distro=esm-apps%2Ffocal"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["1.1.2-1","1.2.0-1","1.3.0-1","1.3.1-1","1.3.1-1ubuntu2","1.3.1-1ubuntu2+esm1"],"ecosystem_specific":{"binaries":[{"binary_version":"1.3.1-1ubuntu2+esm1","binary_name":"php-league-commonmark"}]},"database_specific":{"source":"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-86431.json"}},{"package":{"name":"php-league-commonmark","ecosystem":"Ubuntu:Pro:22.04:LTS","purl":"pkg:deb/ubuntu/php-league-commonmark?arch=source&distro=esm-apps%2Fjammy"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["1.5.7-2build1","1.6.6-1build1","1.6.7-1","1.6.7-1ubuntu0.1~esm1"],"ecosystem_specific":{"binaries":[{"binary_name":"php-league-commonmark","binary_version":"1.6.7-1ubuntu0.1~esm1"}]},"database_specific":{"source":"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-86431.json"}},{"package":{"name":"php-league-commonmark","ecosystem":"Ubuntu:Pro:24.04:LTS","purl":"pkg:deb/ubuntu/php-league-commonmark?arch=source&distro=esm-apps%2Fnoble"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["2.3.9-1","2.4.1-1","2.4.2-1","2.4.2-2","2.4.2-2ubuntu0.1~esm1"],"ecosystem_specific":{"binaries":[{"binary_name":"php-league-commonmark","binary_version":"2.4.2-2ubuntu0.1~esm1"}]},"database_specific":{"source":"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-86431.json"}},{"package":{"name":"php-league-commonmark","ecosystem":"Ubuntu:26.04:LTS","purl":"pkg:deb/ubuntu/php-league-commonmark?arch=source&distro=resolute"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["2.7.0-1","2.7.1-2","2.8.0-1"],"ecosystem_specific":{"binaries":[{"binary_name":"php-league-commonmark","binary_version":"2.8.0-1"}]},"database_specific":{"source":"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-86431.json"}}],"schema_version":"1.9.0","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:N"},{"type":"CVSS_V4","score":"CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:L/VA:N/SC:L/SI:L/SA:N"},{"type":"Ubuntu","score":"medium"}]}