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.
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 (41.4th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 41st percentile — 41.4% 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-8rr7-cvq3-gmfh (vendor-advisory, Mitigation, Vendor Advisory)
- www.vulncheck.com/advisories/commonmark-1.5.0-before-2.10.0-denial-of-service-v… (Third Party Advisory, 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.