CVE-2026-86430: commonmark — Fix

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.

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CVSS v3.1 Score

7.5

HIGH

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

EPSS — Exploit Prediction

0.0029

Probability of exploitation

0.21%

Percentile rank

EPSS estimates the probability that this vulnerability will be exploited in the wild within the next 30 days. A higher score means more likely to be exploited.

Weakness Type (CWE)

CWE-407 CWE-407

Affected Products

Vendor	Product	Versions
thephpleague	commonmark	< 2.9.1

References

Advisories & Patches

https://github.com/thephpleague/commonmark/security/advisories/GHSA-j8pm-gj4c-rq4x

Other References

https://www.vulncheck.com/advisories/league-commonmark-before-2.9.1-denial-of-service-via-parsing

Frequently Asked Questions

What is CVE-2026-86430? +

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. It has a CVSS v3.1 base score of 7.5 (HIGH).

How severe is CVE-2026-86430? +

CVE-2026-86430 has a CVSS v3.1 score of 7.5 out of 10, rated HIGH. This is a high-severity vulnerability that should be prioritized for patching. The EPSS score is 0.0029, placing it in the 0th percentile for exploitation probability.

What products are affected by CVE-2026-86430? +

CVE-2026-86430 affects products from thephpleague, specifically: commonmark. Check the affected products table above for specific version ranges.

How do I check if I'm vulnerable to CVE-2026-86430? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

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