CVE-2026-56434

NGINX ngx_http_ssi_module vulnerability

Assigner: f5
Reserved: 08.07.2026 Published: 15.07.2026 Updated: 15.07.2026

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 heap buffer over-read 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.

Metrics

CVSS Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:H
CVSS Score: 6.5

Attack Vector	Network	Scope	Unchanged
Attack Complexity	High	Confidentiality Impact	None
Privileges Required	None	Integrity Impact	Low
User Interaction	None	Availability Impact	High

CVSS 3.1

CVSS Vector: 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
CVSS Score: 8.3

Exploitability Metrics		Vulnerable System Impact Metrics		Subsequent System Impact Metrics
Attack Vector	Network	Confidentiality	None	Confidentiality	None
Attack Complexity	Low	Integrity	Low	Integrity	None
Attack Requirements	Present	Availability	High	Availability	None
Privileges Required	None
User Interaction	None

CVSS 4.0

Product Status

Vendor	F5
Product	NGINX Plus
Versions	Default: unknown affected from 37.0.0.1 to 37.0.3.1 (excl.) affected from R36 to R36 P7 (excl.) affected from R33 to * (excl.)

Vendor

Product

NGINX Plus

Versions

Default: unknown

affected from 37.0.0.1 to 37.0.3.1 (excl.)
affected from R36 to R36 P7 (excl.)
affected from R33 to * (excl.)

Vendor	F5
Product	NGINX Open Source
Versions	Default: unknown affected from 1.31.2 to 1.31.3 (excl.) affected from 0.8.11 to 1.30.4 (excl.)

Vendor

Product

NGINX Open Source

Versions

Default: unknown

affected from 1.31.2 to 1.31.3 (excl.)
affected from 0.8.11 to 1.30.4 (excl.)

Credits

F5 acknowledges p4p3r(@P4P3R-HAK)" of "싸이버원(CYBERONE) for bringing this issue to our attention and following the highest standards of coordinated disclosure. reporter

References

Problem Types