thephpleague commonmark up to 2.9.0 SmartPunctExtension/AttributesExtension resource consumption

Summaryinfo

A vulnerability categorized as problematic has been discovered in thephpleague commonmark up to 2.9.0. The impacted element is an unknown function of the component SmartPunctExtension/AttributesExtension. The manipulation results in resource consumption. This vulnerability is reported as CVE-2026-86429. The attack can be launched remotely. No exploit exists.

Detailsinfo

A vulnerability classified as problematic has been found in thephpleague commonmark up to 2.9.0. Affected is an unknown functionality of the component SmartPunctExtension/AttributesExtension. The manipulation with an unknown input leads to a resource consumption vulnerability. CWE is classifying the issue as CWE-400. The product does not properly control the allocation and maintenance of a limited resource, thereby enabling an actor to influence the amount of resources consumed, eventually leading to the exhaustion of available resources. This is going to have an impact on availability. CVE summarizes:

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.

The advisory is available at github.com. This vulnerability is traded as CVE-2026-86429 since 09/07/2026. The exploitability is told to be easy. It is possible to launch the attack remotely. The exploitation doesn't require any form of authentication. The technical details are unknown and an exploit is not available. This vulnerability is assigned to T1499 by the MITRE ATT&CK project.

Upgrading to version 2.9.1 eliminates this vulnerability.

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Productinfo

Vendor

• thephpleague

Name

• commonmark

Version

• 2.0
• 2.1
• 2.2
• 2.3
• 2.4
• 2.5
• 2.6
• 2.7
• 2.8
• 2.9.0

Website

• Product: https://github.com/thephpleague/commonmark/

CPE 2.3info

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CPE 2.2info

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