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.
No public exploitation has been reported so far. A fixed version is available (see the table below).
Recommended action: Update to the fixed version listed for your distribution using the native package manager.
Severity metrics
CVSS 4.0 : 8.3 HIGH · CVSS 3.1 : 6.5 MEDIUM
Vector: AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:L/VA:H/SC:N/SI:N/SA:N
Affected & fixed versions by distribution
Versions are the native distribution strings (backport-aware): RHEL/Debian/SUSE backport fixes, so compare with the distro version comparator (dpkg / rpm / vercmp), not the upstream version.
| Distribution | Package | Affected | Fixed version | Status |
|---|---|---|---|---|
| Debian:11 | nginx | - | - | affected (no fix yet) |
| Debian:12 | nginx | - | - | affected (no fix yet) |
| Debian:13 | nginx | - | - | affected (no fix yet) |
| Debian:14 | nginx | - | 1.30.1-7 | fixed |
| Ubuntu:Pro:14.04:LTS | nginx | - | - | affected (no fix yet) |
| Ubuntu:Pro:16.04:LTS | nginx | - | - | affected (no fix yet) |
| Ubuntu:Pro:18.04:LTS | nginx | - | - | affected (no fix yet) |
| Ubuntu:Pro:20.04:LTS | nginx | - | - | affected (no fix yet) |
| Ubuntu:22.04:LTS | nginx | - | 1.18.0-6ubuntu14.17 | fixed |
| Ubuntu:24.04:LTS | nginx | - | 1.24.0-2ubuntu7.14 | fixed |
| Ubuntu:26.04:LTS | nginx | - | 1.28.3-2ubuntu1.7 | fixed |
| openSUSE:Tumbleweed | nginx | - | 1.31.3-1.1 | fixed |