Use After Free in F5 nginx Gateway Fabric
CVE-2026-56434
NGINX Plus and NGINX Open Source have a vulnerability in the ngx_http_ssi_module module. This vulnerability may exist when the Server-Side Includes (SSI), proxy_pass, and proxy_buffering off directives are configured. With this configuration, an unauthenticated attacker with man-in-the-middle (MITM) ability to control responses from an upstream server may be able to cause a use-after-free in the NGINX worker process. This issue may lead to limited modification of memory or a restart of the NGINX worker process. Impact: This vulnerability may allow remote attackers to have limited control to modify memory contents or restart the NGINX worker process. There is no control plane exposure; this is a data plane issue only. Note: Software versions which have reached End of Technical Support (EoTS) are not evaluated.
Vulnerability class: Use-After-Free
Published · last modified .
CVSS v3 metric
CVSS v3 base score 6.5 (Medium). Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:H.
EPSS exploit prediction
EPSS: 0.004 (34.8th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 35th percentile — 34.8% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.004 · newest: 0.004 · change: -0.000
Affected products
- F5 nginx Gateway Fabric
- F5 nginx Ingress Controller — versions 4.0.0, 4.0.1
- F5 nginx Open Source — versions 1.31.2, 0.8.11
- F5 nginx Plus — versions 37.0.0.1, R36, R33
- F5 nginx Plus — versions r36
- F5 Waf
Weakness classification (CWE)
References
- my.f5.com/manage/s/article/K000162098 (vendor-advisory, patch, Vendor Advisory)
Frequently asked questions
- What is CVE-2026-56434?
- CVE-2026-56434 is a medium-severity vulnerability in F5 nginx Gateway Fabric, classified under Use After Free. CVSS score: 6.5/10. Published 2026-07-15.
- How severe is CVE-2026-56434?
- Medium severity. CVSS v3 base score is 6.5 out of 10.