{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-86434","assignerOrgId":"83251b91-4cc7-4094-a5c7-464a1b83ea10","state":"PUBLISHED","assignerShortName":"VulnCheck","dateReserved":"2026-09-07T12:34:31.457Z","datePublished":"2026-09-07T12:53:53.194Z","dateUpdated":"2026-09-07T12:53:53.194Z"},"containers":{"cna":{"providerMetadata":{"orgId":"83251b91-4cc7-4094-a5c7-464a1b83ea10","shortName":"VulnCheck","dateUpdated":"2026-09-07T12:53:53.194Z"},"datePublic":"2026-08-03T00:00:00.000Z","title":"commonmark 2.0.0 through 2.8.3 Denial of Service via Slug Collision","descriptions":[{"lang":"en","value":"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."}],"problemTypes":[{"descriptions":[{"lang":"en","description":"Inefficient Algorithmic Complexity","cweId":"CWE-407","type":"CWE"}]}],"affected":[{"vendor":"thephpleague","product":"commonmark","defaultStatus":"unaffected","versions":[{"version":"2.0.0","status":"affected","versionType":"semver","lessThan":"2.8.4"},{"version":"2.8.4","status":"unaffected","versionType":"semver"}]}],"cpeApplicability":[{"nodes":[{"operator":"OR","negate":false,"cpeMatch":[{"vulnerable":true,"criteria":"cpe:2.3:a:thephpleague:commonmark:*:*:*:*:*:*:*:*","versionStartIncluding":"2.0.0","versionEndExcluding":"2.8.4"}]}]}],"metrics":[{"format":"CVSS","cvssV4_0":{"version":"4.0","vectorString":"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","attackVector":"NETWORK","attackComplexity":"LOW","attackRequirements":"NONE","privilegesRequired":"NONE","userInteraction":"NONE","vulnConfidentialityImpact":"NONE","vulnIntegrityImpact":"NONE","vulnAvailabilityImpact":"HIGH","subConfidentialityImpact":"NONE","subIntegrityImpact":"NONE","subAvailabilityImpact":"NONE","baseScore":8.7,"baseSeverity":"HIGH"}},{"format":"CVSS","cvssV3_1":{"version":"3.1","vectorString":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H","attackVector":"NETWORK","attackComplexity":"LOW","privilegesRequired":"NONE","userInteraction":"NONE","scope":"UNCHANGED","confidentialityImpact":"NONE","integrityImpact":"NONE","availabilityImpact":"HIGH","baseScore":7.5,"baseSeverity":"HIGH"}}],"references":[{"url":"https://github.com/thephpleague/commonmark/security/advisories/GHSA-mh25-x5hq-wrqp","tags":["vendor-advisory"],"name":"GitHub Security Advisory (GHSA-mh25-x5hq-wrqp)"},{"name":"VulnCheck Advisory: commonmark 2.0.0 through 2.8.3 Denial of Service via Slug Collision","tags":["third-party-advisory"],"url":"https://www.vulncheck.com/advisories/commonmark-2.0.0-through-2.8.3-denial-of-service-via-slug-collision"}],"credits":[{"lang":"en","value":"GrahamCampbell","type":"finder"}],"x_generator":{"engine":"vulncheck-endgame"}}}}