CVE-2026-40701Network attack vector

Worker restart via OCSP resolver use-after-free

Published May 13, 2026 · Updated May 13, 2026

Heap use-after-free in F5 NGINX Plus and NGINX Open Source allows remote attackers to restart workers or modify limited data. The ngx_http_ssl_module OCSP resolver path dereferences heap state after its lifetime ends during client-certificate verification. Reachability requires ssl_verify_client on or optional together with ssl_ocsp on, or leaf parameters using a resolver; exploitation depends on conditions outside attacker control.

CVSS severity4.8
Medium
EPSS probability0.69%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Heap use-after-free in F5 NGINX Plus and NGINX Open Source allows remote attackers to restart workers or modify limited data. The ngx_http_ssl_module OCSP resolver path dereferences heap state after its lifetime ends during client-certificate verification. Reachability requires ssl_verify_client on or optional together with ssl_ocsp on, or leaf parameters using a resolver; exploitation depends on conditions outside attacker control.

The record

CVE
CVE-2026-40701
Published
May 13, 2026
Updated
May 13, 2026
Vendor
F5 Networks
Product
NGINX Open Source
Classifications
CWE-416, T1190
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. May 13, 2026CVE publishedPublication date reported by the CVE source.
  2. May 13, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=1.19.0 <1.30.1

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

F5 Networks · NGINX Open Sourceversion=1.19.0 <1.30.1
F5 Networks · NGINX Plusversion=R32 <R32 P6; version=R36 <R36 P4

Published CVSS scores

6.3F5CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:L/VI:N/VA:L/SC:N/SI:N/SA:N
4.8F5CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:L

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-416Use After Free
T1190Exploit Public-Facing Application

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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