Use After Free in F5 Nginx Open Source
CVE-2026-40701
NGINX Plus and NGINX Open Source have a vulnerability in the ngx_http_ssl_module module when the ssl_verify_client directive is set to "on" or "optional," and the ssl_ocsp directive is set to "on" or the leaf parameters are configured with…
Vulnerability class: Use-After-Free
EPSS: 0.000 (13.9th percentile) — read the EPSS interpretation.
CVSS v3 metric
CVSS v3 base score 4.8 (Medium). Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:L.
Affected products
- F5 Nginx Open Source — versions 1.31.0, 1.19.0
- F5 Nginx Plus — versions R37, R36, R32
Weakness classification (CWE)
Public proof-of-concept exploits
References
- f5sirt@f5.com (vendor-advisory, patch)
Frequently asked questions
- What is CVE-2026-40701?
- CVE-2026-40701 is a medium-severity vulnerability in F5 Nginx Open Source, classified under Use After Free. CVSS score: 4.8/10. Published 2026-05-13.
- How severe is CVE-2026-40701?
- Medium severity. CVSS v3 base score is 4.8 out of 10.
- Is CVE-2026-40701 known to be exploited?
- 1 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.