What is CVE-2026-86433?

CVE-2026-86433 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-2026-86433?

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

Vulnerability in Thephpleague Commonmark

CVE-2026-86433

commonmark versions from 1.5.0 before 2.8.4 contain a denial of service vulnerability in the Attributes extension where AttributesListener::findTargetAndDirection() performs quadratic-time sibling list scanning. Unauthenticated attackers can submit approximately 32 KB of repeated attribute blocks to cause parsing to take over 5 seconds, exhausting 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-2026-86433?: CVE-2026-86433 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-2026-86433?: High severity. CVSS v3 base score is 7.5 out of 10.