{"id":"UBUNTU-CVE-2026-86434","details":"league/commonmark versions \u003e= 2.0.0 and \u003c 2.8.4 (patched in 2.9.0) contain a denial of service vulnerability in UniqueSlugNormalizer::normalize(), which restarts its numeric-suffix search from 1 on every slug collision, resulting in O(K^2) time complexity for K headings that collapse to the same base slug. The vulnerable path is reached when HeadingPermalinkExtension, FootnoteExtension, or TableOfContentsExtension is registered. An unauthenticated attacker can force many headings onto a single base slug (e.g., via empty ATX headings, identical heading text, or punctuation-only headings) in a small Markdown document, consuming excessive CPU and denying service.","modified":"2026-09-16T14:03:37.990171577Z","published":"2026-09-07T13:20:00Z","upstream":["CVE-2026-86434"],"references":[{"type":"REPORT","url":"https://ubuntu.com/security/CVE-2026-86434"},{"type":"REPORT","url":"https://www.cve.org/CVERecord?id=CVE-2026-86434"},{"type":"REPORT","url":"https://github.com/thephpleague/commonmark/security/advisories/GHSA-mh25-x5hq-wrqp"}],"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_name":"php-league-commonmark","binary_version":"1.3.1-1ubuntu2+esm1"}]},"database_specific":{"source":"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-86434.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_version":"1.6.7-1ubuntu0.1~esm1","binary_name":"php-league-commonmark"}]},"database_specific":{"source":"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-86434.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_version":"2.4.2-2ubuntu0.1~esm1","binary_name":"php-league-commonmark"}]},"database_specific":{"source":"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-86434.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-2026-86434.json"}}],"schema_version":"1.9.0","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H"},{"type":"CVSS_V4","score":"CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N"},{"type":"Ubuntu","score":"medium"}]}