What is CVE-2026-86428?

CVE-2026-86428 is a high-severity vulnerability in Thephpleague Commonmark, classified under Inefficient Algorithmic Complexity. CVSS score: 7.5/10. Published 2026-09-07.

How severe is CVE-2026-86428?

High severity. CVSS v3 base score is 7.5 out of 10.

Vulnerability in Thephpleague Commonmark

CVE-2026-86428

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.

CVSS v3 metric

CVSS v3 base score 7.5 (High). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H.

Affected products

Thephpleague Commonmark

Weakness classification (CWE)

CWE-407 — Inefficient Algorithmic Complexity

References

disclosure@vulncheck.com (vendor-advisory)
disclosure@vulncheck.com (third-party-advisory)

Frequently asked questions

What is CVE-2026-86428?: CVE-2026-86428 is a high-severity vulnerability in Thephpleague Commonmark, classified under Inefficient Algorithmic Complexity. CVSS score: 7.5/10. Published 2026-09-07.
How severe is CVE-2026-86428?: High severity. CVSS v3 base score is 7.5 out of 10.