{"id":"DEBIAN-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":"2026-09-29T13:04:29.645564779Z","published":"2026-09-07T13:20:42.460Z","upstream":["CVE-2026-86431"],"references":[{"type":"ADVISORY","url":"https://security-tracker.debian.org/tracker/CVE-2026-86431"}],"affected":[{"package":{"name":"php-league-commonmark","ecosystem":"Debian:12","purl":"pkg:deb/debian/php-league-commonmark?arch=source&distro=bookworm"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["2.10.0-1","2.10.1-1","2.10.3-1","2.3.9-1","2.3.9-1+deb12u1","2.4.0-1","2.4.1-1","2.4.2-1","2.4.2-2","2.5.0-1","2.5.1-1","2.5.3-1","2.6.0-1","2.6.1-1","2.6.1-2","2.6.2-1","2.7.0-1","2.7.1-1","2.7.1-2","2.8.0-1","2.8.1-1","2.8.2-1","2.8.2-2","2.8.3-1","2.9.0-1"],"ecosystem_specific":{"urgency":"not yet assigned"},"database_specific":{"source":"https://storage.googleapis.com/osv-test-debian-osv/debian-cve-osv/DEBIAN-CVE-2026-86431.json"}},{"package":{"name":"php-league-commonmark","ecosystem":"Debian:13","purl":"pkg:deb/debian/php-league-commonmark?arch=source&distro=trixie"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["2.10.0-1","2.10.1-1","2.10.3-1","2.7.0-1","2.7.0-1+deb13u1","2.7.1-1","2.7.1-2","2.8.0-1","2.8.1-1","2.8.2-1","2.8.2-2","2.8.3-1","2.9.0-1"],"ecosystem_specific":{"urgency":"not yet assigned"},"database_specific":{"source":"https://storage.googleapis.com/osv-test-debian-osv/debian-cve-osv/DEBIAN-CVE-2026-86431.json"}},{"package":{"name":"php-league-commonmark","ecosystem":"Debian:14","purl":"pkg:deb/debian/php-league-commonmark?arch=source&distro=forky"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"2.10.0-1"}]}],"versions":["2.7.0-1","2.7.1-1","2.7.1-2","2.8.0-1","2.8.1-1","2.8.2-1","2.8.2-2","2.8.3-1","2.9.0-1"],"ecosystem_specific":{"urgency":"not yet assigned"},"database_specific":{"source":"https://storage.googleapis.com/osv-test-debian-osv/debian-cve-osv/DEBIAN-CVE-2026-86431.json"}}],"schema_version":"1.9.0","severity":[{"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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X"}]}