What is 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 a resolver. With this configuration, an unauthenticated attacker can send requests along with conditions beyond its control that may cause a heap-use-after-free error in the NGINX worker process. This vulnerability may result in limited modification of data or the NGINX worker process restarting. Note: Software versions which have reached End of Technical Support (EoTS) are not evaluated.
The record classifies CVE-2026-40701 under weakness class CWE-416. Its CVSS v3 base vector states that the flaw is reachable remotely over the network, needs no prior authentication, needs no user interaction. 2 affected-product entries are recorded, across 1 vendor, listed below. The identifier was first published 167 days ago.
Severity and exploitation probability
- CVSS v3.1 base score
- 4.8 — MEDIUM
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:L - CVSS v4.0 base score
- 6.3
CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:L/VI:N/VA:L/SC:N/SI:N/SA:N - EPSS (FIRST)
- 0.6% probability of exploitation in the next 30 days, higher than 51.3% of all scored CVEs
- CISA KEV
- Not listed in the CISA Known Exploited Vulnerabilities catalog
- Threadlinqs priority
- 6.5/10 — a Threadlinqs composite of the CVSS base score, the EPSS percentile and public exploit availability
- Published
- 2026-05-13
Is CVE-2026-40701 being exploited?
Weaponised exploit code for CVE-2026-40701 is publicly available. 1 public proof-of-concept repository is tracked for this identifier. It currently carries a trending score of 26 in the Threadlinqs vulnerability feed.
- edgecases-PurpleHax/cve-images (github)
Affected products and versions
- F5: NGINX Plus, NGINX Open Source
How to fix CVE-2026-40701
Vendor advisory: https://my.f5.com/manage/s/article/K000161021. Apply the vendor fix referenced above to every affected product listed in this record, then confirm the running version against the vendor advisory.
Threat activity tracking CVE-2026-40701
1 tracked threat in the Threadlinqs corpus references CVE-2026-40701, either in the campaign’s CVE list or as an indicator on the campaign record.
Sources
Enriched from CVE.org, NVD, FIRST EPSS, public proof-of-concept repositories. Last verified by Threadlinqs on . This product uses the NVD API but is not endorsed or certified by the NVD.