What’s Vulnerable › Vulnerabilities

CVE-2026-86433: commonmark 1.5.0 before 2.8.4 Denial of Service via Attributes

• Severity: high (CVSS 7.5 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.5% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-09-07 · updated 2026-10-08
• Weakness: CWE-407

Description

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

How to fix

Upgrade to a fixed version: thephpleague commonmark 2.8.4. Check the vendor advisory for mitigations.

References

• https://github.com/thephpleague/commonmark/security/advisories/GHSA-g2gp-3wwq-f4ph
• https://www.vulncheck.com/advisories/commonmark-1.5.0-before-2.8.4-denial-of-service-via-attributes

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