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.
Published · last modified .
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.
EPSS exploit prediction
EPSS: 0.005 (41.0th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 41st percentile — 41.0% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.003 · newest: 0.005 · change: +0.002
Affected products
Weakness classification (CWE)
References
- github.com/thephpleague/commonmark/security/advisories/GHSA-jfm3-95jq-q3rf (vendor-advisory)
- www.vulncheck.com/advisories/commonmark-1.5.0-before-2.8.4-denial-of-service-vi… (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.