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CVE-2026-86428

7.5 · HIGH

commonmark versions from 1.5.0 before 2.10.0 contain a denial of service vulnerability in the AttributesExtension when processing distinctly-named attributes.

Published Sep 7, 2026thephpleagueCWE-407EPSS 0.49%

Overview

CVE-2026-86428 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

commonmark versions from 1.5.0 before 2.10.0 contain a denial of service vulnerability in the AttributesExtension when processing distinctly-named attributes. Attackers can submit Markdown with numerous distinct attribute names to cause quadratic-time attribute merging and filtering, consuming disproportionate CPU resources and preventing legitimate requests from completing.

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, < 2.10.0Affected

References

GitHubgithub.com/thephpleague/commonmark/security/advisories/GHSA-8rr7-cvq3-gmfhRefwww.vulncheck.com/advisories/commonmark-1.5.0-before-2.10.0-denial-of-service-via-attributes

How CyberStrike helps

Frequently asked questions

What is CVE-2026-86428?

CVE-2026-86428 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-2026-86428?

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-2026-86428?

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-2026-86428?

CyberStrike is an open-source, AI-augmented pentesting engine. Rather than flag a version number, it tests whether an issue like CVE-2026-86428 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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