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CVE-2026-86429

7.5 · HIGH

The league/commonmark (thephpleague/commonmark) library in versions >= 1.5.0 and < 2.9.1 contains quadratic parsing complexity in its SmartPunctExtension and AttributesExtension.

Published Sep 7, 2026thephpleagueCWE-407EPSS 0.52%

Overview

CVE-2026-86429 is a high-severity vulnerability affecting thephpleague commonmark. It was published on September 7, 2026 and has a CVSS 3.1 base score of 7.5 (HIGH).

This vulnerability has a CVSS 3.1 base score of 7.5, rated HIGH. It can be exploited remotely over the network. No authentication or special privileges are required for exploitation.

Technical description

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.

Remediation

Check the references section for vendor advisories and patches from thephpleague. Update commonmark to the latest patched version. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

Affected products

VendorProductVersionsStatus
thephpleaguecommonmark>= 1.5.0, < 2.9.1Affected

References

GitHubgithub.com/thephpleague/commonmark/security/advisories/GHSA-jjv6-8j6v-6j52Refwww.vulncheck.com/advisories/commonmark-before-2.9.1-denial-of-service-via-smartpunct-and-attributes

How CyberStrike helps

Frequently asked questions

What is CVE-2026-86429?

CVE-2026-86429 is a high-severity vulnerability affecting thephpleague commonmark. It was published on September 7, 2026 and has a CVSS 3.1 base score of 7.5 (HIGH).

How severe is CVE-2026-86429?

This vulnerability has a CVSS 3.1 base score of 7.5, rated HIGH. It can be exploited remotely over the network. No authentication or special privileges are required for exploitation.

How do I fix or remediate CVE-2026-86429?

Check the references section for vendor advisories and patches from thephpleague. Update commonmark to the latest patched version. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

How can CyberStrike help with CVE-2026-86429?

CyberStrike is an open-source, AI-augmented pentesting engine. Rather than flag a version number, it tests whether an issue like CVE-2026-86429 is actually reachable in your own applications and APIs, then verifies each finding before reporting it. That tells you if the weakness is a real, exploitable risk in your environment or a false positive you can safely deprioritize.

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