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CVE-2026-86430

7.5 · HIGH

league/commonmark versions before 2.9.1 contain multiple denial of service vulnerabilities in fenced code block detection, reference link label lookup, and emphasis delimiter processing that perfor…

Published Sep 7, 2026thephpleagueCWE-407EPSS 0.49%

Overview

CVE-2026-86430 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

league/commonmark versions before 2.9.1 contain multiple denial of service vulnerabilities in fenced code block detection, reference link label lookup, and emphasis delimiter processing that perform super-linear work on crafted input. Attackers can submit specially crafted Markdown with long backtick runs, nested brackets, or delimiter sequences to consume disproportionate CPU time and prevent 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>= 0, < 2.9.1Affected

References

GitHubgithub.com/thephpleague/commonmark/security/advisories/GHSA-j8pm-gj4c-rq4xRefwww.vulncheck.com/advisories/league-commonmark-before-2.9.1-denial-of-service-via-parsing

How CyberStrike helps

Frequently asked questions

What is CVE-2026-86430?

CVE-2026-86430 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-2026-86430?

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-2026-86430?

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-2026-86430?

CyberStrike is an open-source, AI-augmented pentesting engine. Rather than flag a version number, it tests whether an issue like CVE-2026-86430 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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