Denial of Service Vulnerability in CommonMark by The PHP League
CVE-2026-86428

8.7HIGH

Key Information:

Vendor

ThePHPleague

Status
Commonmark
Vendor
CVE Published:
7 September 2026

What is CVE-2026-86428?

CommonMark versions prior to 2.10.0 exhibit a denial of service vulnerability due to inefficiencies in the AttributesExtension. When processing Markdown with multiple distinct attribute names, attackers can exploit this flaw to produce a quadratic-time algorithm's behavior, leading to excessive CPU resource consumption. This results in the potential disruption of legitimate requests, affecting the service availability and user experience.

Affected Version(s)

commonmark 1.5.0 < 2.10.0

commonmark 2.10.0

References

https://github.com/thephpleague/commonmark/security/advis...
vendor-advisory
https://www.vulncheck.com/advisories/commonmark-1.5.0-bef...
third-party-advisory

CVSS V4

Score:
8.7
Severity:
HIGH
Confidentiality:
None
Integrity:
None
Availability:
High
Attack Vector:
Network
Attack Complexity:
Low
Attack Required:
None
Privileges Required:
Undefined
User Interaction:
None

Timeline

  • Vulnerability published

  • Vulnerability Reserved

Credit

manus-use
.