Disclosure summary
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.
Source-reported weakness categories
CWE-407
Source-specific records & product guidance
Sources retain their own attribution and scoring. Follow the original record to confirm affected versions, fixed releases, and configuration conditions.
NIST National Vulnerability Database · NVD-CVE-2026-86429
Open original source · Updated Oct 08, 2026
Only CPE matches marked vulnerable=true are indexed. AND/OR platform conditions must be checked in the original NVD record.
| Vendor | Product / association | Version / bounds |
|---|---|---|
| thephpleague | commonmark | * {"versionStartIncluding":"1.5.0","versionEndExcluding":"2.9.1"} |
Original records & references
- NIST NVD record
- CVE Program record
- github.com — Mitigation, Vendor Advisory
- www.vulncheck.com — Third Party Advisory
PUBLISHED 2026-09-07T09:20:42-04:00
MODIFIED 2026-10-08T12:17:57-04:00
INGESTED 2026-10-10T20:50:36-04:00