{"id":"CVE-2026-86434","summary":"commonmark 2.0.0 through 2.8.3 Denial of Service via Slug Collision","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.","aliases":["GHSA-mh25-x5hq-wrqp"],"modified":"2026-10-20T12:02:32.602307915Z","published":"2026-09-07T12:53:53.194Z","database_specific":{"cna_assigner":"VulnCheck","cwe_ids":["CWE-407"],"osv_generated_from":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/86xxx/CVE-2026-86434.json","unresolved_ranges":[{"extracted_events":[{"introduced":"2.0.0"},{"fixed":"2.8.4"}],"source":"AFFECTED_FIELD"},{"extracted_events":[{"introduced":"2.0.0"},{"fixed":"2.8.4"}],"source":"CPE_FIELD"}]},"references":[{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/86xxx/CVE-2026-86434.json"},{"type":"ADVISORY","url":"https://github.com/thephpleague/commonmark/security/advisories/GHSA-mh25-x5hq-wrqp"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-86434"},{"type":"ADVISORY","url":"https://www.vulncheck.com/advisories/commonmark-2.0.0-through-2.8.3-denial-of-service-via-slug-collision"}],"affected":[{"ranges":[{"type":"GIT","repo":"https://github.com/thephpleague/commonmark","events":[{"introduced":"0"},{"fixed":"5703d83ba3da3b2e356a5fedc848ed6d8ffb6529"}],"database_specific":{"extracted_events":[{"range":[{"introduced":"0"},{"fixed":"2.9.0"}],"source":"DESCRIPTION"}]}}],"versions":["2.8.0","2.7.0","2.6.0","2.5.0","2.4.0","2.3.0","2.2.0","2.1.0","2.0.2","2.0.1","2.0.0","2.0.0-rc2","2.0.0-rc1","2.0.0-beta3","2.0.0-beta2","2.0.0-beta1","0.18.1","0.17.4","0.17.2","0.17.0","0.16.0","0.15.7","0.15.6","0.15.5","0.15.4","0.15.3","0.15.2","0.15.1","0.15.0","0.14.0","0.13.4","0.13.3","0.13.2","0.13.1","0.13.0","0.12.0","0.11.3","0.11.2","0.11.1","0.11.0","0.10.0","0.9.0","0.8.0","0.7.1","0.7.0","0.6.1","0.6.0","0.5.1","0.5.0","0.4.0","0.3.0","0.2.1","0.2.0","0.1.2","0.1.1","0.1.0"],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-86434.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:N/VI:N/VA:H/SC:N/SI:N/SA:N"}]}