CVE-2026-86433: Thephpleague Commonmark

High severity, CVSS 7.5. EPSS: 0.5% chance of exploitation in the next 30 days.

commonmark versions from 1.5.0 before 2.8.4 contain a denial of service vulnerability in the Attributes extension where AttributesListener::findTargetAndDirection() performs quadratic-time sibling list scanning. Unauthenticated attackers can submit approximately 32 KB of repeated attribute blocks to cause parsing to take over 5 seconds, exhausting server resources.

Affected products

• Thephpleague Commonmark: from 1.5.0, before 2.8.4 (fixed in 2.8.4)

Published 2026-09-07. Last modified 2026-10-08.