{"id":"CVE-2026-86434","revision":"fc4dd4bd579f4d6b831f4c1e36bee4df","records":[{"revision":"fc4dd4bd579f4d6b831f4c1e36bee4df","observedAt":"2026-10-23T15:48:27.903+00:00","statement":{"source":"cve-program","id":"CVE-2026-86434","aliases":[],"title":"commonmark 2.0.0 through 2.8.3 Denial of Service via Slug Collision","description":"league/commonmark versions >= 2.0.0 and < 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.","state":0,"publishedAt":"2026-09-07T12:53:53.194+00:00","modifiedAt":"2026-10-08T15:25:54.536+00:00","affected":[{"ecosystem":"Vendor product","name":"commonmark","ranges":[],"versions":[],"rawVersionEvidence":"{\n                    \"vendor\": \"thephpleague\",\n                    \"product\": \"commonmark\",\n                    \"defaultStatus\": \"unaffected\",\n                    \"versions\": [\n                        {\n                            \"version\": \"2.0.0\",\n                            \"status\": \"affected\",\n                            \"versionType\": \"semver\",\n                            \"lessThan\": \"2.8.4\"\n                        },\n                        {\n                            \"version\": \"2.8.4\",\n                            \"status\": \"unaffected\",\n                            \"versionType\": \"semver\"\n                        }\n                    ],\n                    \"packageURL\": \"pkg:composer/league/commonmark\"\n                }"}],"metrics":[{"system":"CVSS 4.0","vector":"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","score":8.7,"severity":"HIGH"},{"system":"CVSS 3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H","score":7.5,"severity":"HIGH"}],"references":["https://github.com/thephpleague/commonmark/security/advisories/GHSA-mh25-x5hq-wrqp","https://www.vulncheck.com/advisories/commonmark-2.0.0-through-2.8.3-denial-of-service-via-slug-collision"],"sourceUrl":"https://www.cve.org/CVERecord?id=CVE-2026-86434","license":"CVE Program Terms of Use","key":"cve-program:CVE-2026-86434","identifiers":["CVE-2026-86434"]},"retained":false,"historicalAffected":[]}],"coverage":[]}