Heap Buffer Overflow in NGINX

CVE-2026-15176 is a heap buffer overflow vulnerability affecting NGINX Plus and NGINX Open Source. The vulnerability arises when specific configuration directives are combined within an NGINX location block: the alias directive used in conjunction with a rewrite directive, or a set or return directive that references the $request_filename variable. Additionally, the vulnerability can be triggered if the $request_filename variable is included in an access log format directive.

An unauthenticated remote attacker can exploit this flaw by sending crafted HTTP requests that trigger the buffer overflow within the NGINX worker process. While the primary documented impact is a denial-of-service condition resulting from worker process restarts, the memory corruption potentially allows for arbitrary code execution in environments where Address Space Layout Randomization (ASLR) is disabled or successfully bypassed. This is a data plane vulnerability and does not affect the NGINX control plane.

Impact

Successful exploitation of CVE-2026-15176 leads to worker process crashes, causing intermittent or persistent denial-of-service conditions for the affected web service. In sophisticated scenarios, the heap overflow primitive may enable remote code execution, threatening the confidentiality, integrity, and availability of the host server. The vulnerability impacts all NGINX Open Source and NGINX Plus installations utilizing the vulnerable directive combinations, posing a significant risk to internet-facing web infrastructure.

Recommendation

Prioritize auditing NGINX configuration files to identify the use of the alias directive in combination with rewrite, set, or return directives that reference $request_filename.

• Review all custom 'log_format' configurations to ensure the $request_filename variable is not utilized in production access logs until a vendor patch is applied.
• Monitor NGINX error logs for unexpected worker process crashes or segmentation faults, which may indicate exploitation attempts.
• Apply patches provided by F5 for NGINX Plus and NGINX Open Source as soon as they become available for your specific deployment version.
• Ensure Address Space Layout Randomization (ASLR) is enabled and enforced at the operating system level for all NGINX host environments to increase the cost of exploitation.