What is CVE-2026-86430?

CVE-2026-86430 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-2026-86430?

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

Vulnerability in Thephpleague Commonmark

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.

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-2026-86430?: CVE-2026-86430 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-2026-86430?: High severity. CVSS v3 base score is 7.5 out of 10.