What is CVE-2026-86435?

CVE-2026-86435 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-2026-86435?

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

Vulnerability in Thephpleague Commonmark

CVE-2026-86435

commonmark versions from 1.5.0 before 2.8.4 contain a denial of service vulnerability in the Footnote extension that fails to deduplicate footnote definitions. Attackers can craft documents with duplicate footnote definitions and references to create quadratic output expansion, consuming excessive memory and CPU to exhaust server resources.

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-2026-86435?: CVE-2026-86435 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-2026-86435?: High severity. CVSS v3 base score is 7.5 out of 10.