The league/commonmark (thephpleague/commonmark) library in versions >= 1.5.0 and < 2.9.1 contains quadratic parsing complexity in its SmartPunctExtension and AttributesExtension. When either extension is explicitly registered on the Environment (they are not enabled by default and are excluded from the standard CommonMark and GitHub-Flavored Markdown converters), an unauthenticated attacker can submit small, specially crafted Markdown documents — such as text alternating with unpaired quotes, contiguous runs of block-level attribute blocks, or repeated class attributes — to trigger disproportionate CPU consumption and cause a denial of service. Fixed in 2.9.1.
Fix
Patch, vendor advisory and mitigation references on NVD 1
- https://github.com/thephpleague/commonmark/security/advisories/GHSA-jjv6-8j6v-6j52 Mitigation, Vendor Advisory
Every line above is quoted from NVD, CISA, Microsoft, the vendor's own advisory or DISA; nothing is generated.
Change history 1
- First seenCVSS 8.7 · thephpleagueNVD modified 2026-10-08 16:17
Affected (CPE criteria) 1
cpe:2.3:a:thephpleague:commonmark:*:*:*:*:*:*:*:*
References 2
- https://github.com/thephpleague/commonmark/security/advisories/GHSA-jjv6-8j6v-6j52 Mitigation, Vendor Advisory
- https://www.vulncheck.com/advisories/commonmark-before-2.9.1-denial-of-service-via-smartpunct-and-attributes Third Party Advisory