High [CVE-2026-56434] NGINX Plus and NGINX Open Source have a vulnerability in the ngx_http_ssi_module module
This high-severity F5 advisory covers CVE-2026-56434 affecting NGINX Plus, NGINX Open Source.
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Summary
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: 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.
- NGINX Plus 37.0.0.1 before 37.0.3.1
- NGINX Plus R36 before R36 P7
- NGINX Plus R33
- NGINX Open Source 1.31.2 before 1.31.3
- NGINX Open Source 0.8.11 before 1.30.4
Official advisory · high-confidence parse· fetched 2 months ago·verify at source
- 37.0.3.1
- R36 P7
- 1.31.3
- 1.30.4
Official advisory · high-confidence parse· fetched 2 months ago·verify at source
Mitigation
Upgrade to a fixed release: 37.0.3.1, R36 P7, 1.31.3, 1.30.4. That is the remediation for this advisory.
The vendor advisory may list additional interim mitigations or workarounds not captured here — review it before change work.
Official advisory · high-confidence parse· fetched 2 months ago·verify at source
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