CVE-2026-56434: F5 Nginx Gateway Fabric

Medium severity, CVSS 6.5. EPSS: 0.4% chance of exploitation in the next 30 days.

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.

Affected products

• F5 Nginx Gateway Fabric: from 1.3.0, up to and including 1.6.2; from 2.0.0, before 2.6.7 (fixed in 2.6.7)
• F5 Nginx Ingress Controller: from 3.5.0, up to and including 3.7.2; from 5.0.0, before 5.5.3 (fixed in 5.5.3); from 2026-lts-r1, before 2026-lts-r4 (fixed in 2026-lts-r4); version 4.0.0 only; version 4.0.1 only
• F5 Nginx Plus: from 37.0.0.1, before 37.0.3.1 (fixed in 37.0.3.1); from r33, before r36 (fixed in r36); version r36 only
• F5 Waf: from 4.11.0, up to and including 4.16.0; from 5.2.0, up to and including 5.8.0; from 5.9.0, before 5.13.4 (fixed in 5.13.4)

Published 2026-07-15. Last modified 2026-08-10.