CVE-2026-56434 NGINX ngx_http_ssi_module vulnerability
An unauthenticated attacker with MITM capabilities can trigger a use-after-free in NGINX, causing worker restarts or limited memory modification.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-56434?
CVE-2026-56434 is a high-severity use after free vulnerability in F5 NGINX Open Source, published on 15 Jul 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
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.
Weakness: CWE-416
Which versions are affected by CVE-2026-56434?
2 open source packages ship an affected version, including nginx and nginx-gateway. It affects 4 products.
| Package | Affected | Fixed in |
|---|---|---|
nginx Bitnami | From 0.8.11 | 1.30.4, 1.31.3 |
nginx-gateway Bitnami | From 0.8.11 | 1.30.4, 1.31.3 |
Products include F5 Nginx Gateway Fabric, F5 Nginx Ingress Controller, F5 Nginx Plus, F5 Waf.
How do I fix CVE-2026-56434?
Upgrade nginx to a fixed version for your release line: 1.30.4 or 1.31.3.
Upgrade to the fixed version. These bugs are found with fuzzing and sanitisers and avoided by memory-safe languages. More about Use after free.
Is CVE-2026-56434 being exploited?
There is no known exploitation of CVE-2026-56434 in the wild and no public exploit code.
Other vulnerabilities in F5 NGINX Open Source
Sources
Also known as ALPINE-CVE-2026-56434, AZL-92496, BELL-CVE-2026-56434, BIT-nginx-2026-56434, BIT-nginx-gateway-2026-56434, CLSA-2026-1787916225 and 17 more.