Heap-based buffer overflow in NGINX Open Source and NGINX Plus - CVE-2026-9256
Published: May 25, 2026
Vulnerability identifier: #VU132220
CSH Severity: Critical
CVSS v4.0: CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/E:U/U:Red
CVE-ID: CVE-2026-9256
CWE-ID: CWE-122
Exploitation vector: Remote access
Exploit availability:
No public exploit available
Vendor: F5 Networks
Affected software:
NGINX Open Source
NGINX Plus
NGINX Open Source
NGINX Plus
Detailed vulnerability description
The vulnerability allows a remote attacker to compromise the affected system.
The vulnerability exists due to heap-based buffer overflow in ngx_http_rewrite_module when processing crafted HTTP requests that trigger rewrite directives using overlapping PCRE captures and multiple capture references in a redirect or arguments context. A remote attacker can send crafted HTTP requests to execute arbitrary code or crash the web server.
There is no control plane exposure; this is a data plane issue only. Code execution is possible on systems with ASLR disabled or when ASLR can be bypassed.
How to mitigate CVE-2026-9256
Install security update from vendor's website.