CVE-2026-86429

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.

CVSS v3 7.5 HIGH

7.5^/10

CVSS v3 : HIGH

Vector :

Exploitability : 3.9 / Impact : 3.6

Attack Vector NETWORK

Attack Complexity LOW

Privileges Required NONE

User Interaction NONE

Confidentiality Impact NONE

Integrity Impact NONE

Availability Impact HIGH

Scope UNCHANGED

References

Link	Resource
https://github.com/thephpleague/commonmark/security/advisories/GHSA-jjv6-8j6v-6j52	Vendor Advisory Mitigation
https://www.vulncheck.com/advisories/commonmark-before-2.9.1-denial-of-service-via-smartpunct-and-attributes	Third Party Advisory

Configurations

Configuration 1 (hide)

cpe:2.3:a:thephpleague:commonmark:*:*:*:*:*:*:*:*

History

No history.

Information

Published : 2026-09-07 13:20

Updated : 2026-09-09 16:29

NVD link : CVE-2026-86429

Mitre link : CVE-2026-86429

CVE.ORG link : CVE-2026-86429

JSON object : View

Products Affected

thephpleague

commonmark

CWE

CWE-407

Inefficient Algorithmic Complexity

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