{"id":"CVE-2026-86434","title":"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^…","summary":"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^…","severity":"high","cvss":7.5,"cvssVector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H","cwe":["CWE-407"],"vendor":"thephpleague","product":"commonmark","affected":["commonmark >= 2.0.0 < 2.8.4"],"published":"2026-09-07","updated":"2026-09-19","sourceUpdated":"2026-09-19T15:17:06.503","source":"NVD","sourceUrl":"https://nvd.nist.gov/vuln/detail/CVE-2026-86434","references":[{"url":"https://github.com/thephpleague/commonmark/security/advisories/GHSA-mh25-x5hq-wrqp","label":"disclosure@vulncheck.com"},{"url":"https://www.vulncheck.com/advisories/commonmark-2.0.0-through-2.8.3-denial-of-service-via-slug-collision","label":"disclosure@vulncheck.com"}],"tags":["nvd","cve.org"],"epss":0.00509,"epssPercentile":0.40892,"ssvc":{"exploitation":"none","automatable":"yes","technicalImpact":"partial","timestamp":"2026-09-18T17:42:05.970571Z"},"ingestedAt":"2026-09-08T20:10:03.179Z","slug":"CVE-2026-86434","body":"## Overview\n\nleague/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.\n\n## Remediation\n\nRefer to the linked advisories for vendor-supplied fixes and affected version ranges.","depth":"twilight","depthScore":41,"depthScoreParts":{"impact":41.3,"likelihood":0.1,"exploitation":0,"ransomware":0},"changes":[]}