F5 NGINX: use after free
High8.3CVE-2026-56434 · Published Jul 15, 2026 · updated Aug 10, 2026
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 versions
| Package | Affected | Fixed in |
|---|---|---|
| NGINX Open Source Product | >= 1.31.2, < 1.31.3 | 1.31.3 |
| >= 0.8.11, < 1.30.4 | 1.30.4 | |
| NGINX Plus Product | >= 37.0.0.1, < 37.0.3.1 | 37.0.3.1 |
| >= R36, < R36 P7 | R36 P7 | |
| <= R33 | No fix yet |
Details and references
- CVSS 4.0
- CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:L/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
- Severity from
- the vendor (its own CVE record or advisory)
- Weakness
- CWE-416
More F5 advisories
All F5| Date | Advisory | Severity | Fixed in |
|---|---|---|---|
| Jul 15 | F5 NGINX: uninitialized resource | High8.8 | Plus 37.0.3.1+3 more |
| Jul 15 | F5 NGINX: path traversal | Medium5.3 | 2.47.0+1 more |
| Jul 15 | F5 NGINX Plus: out-of-bounds read | Medium6.3 | 37.0.3.1+1 more |
| Jul 15 | F5 BIG-IP: denial of service | High8.7 | 21.1.0.1+7 more |
| Jul 15 | When NGINX Ingress Controller is configured with Custom Resource Definitions | High8.7 | 5.5.2+1 more |
| Jul 15 | F5 NGINX Ingress Controller: denial of service | High7.1 | 5.5.2+1 more |