CVE-2026-15176 in NGINX Plus
Summary
by MITRE • 10/14/2026
A vulnerability exists in NGINX Plus and NGINX Open Source when a location is configured that uses the alias directive together with rewrite and a set or return directive referencing the $request_filename variable. Alternatively, the same result could be achieved when the $request_filename variable is used in an access log format directive. An unauthenticated attacker along with conditions beyond their control can exploit this vulnerability by sending crafted HTTP requests. This may cause a heap buffer overflow in the NGINX worker process leading to a restart. Additionally, attackers can execute code on systems with Address Space Layout Randomization (ASLR) disabled or when the attacker can bypass ASLR.
Impact: This vulnerability may allow remote attackers to cause a denial-of-service (DoS) on the NGINX system or to possibly trigger a code execution. 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.
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Analysis
by VulDB Data Team • 10/14/2026
The identified vulnerability resides within the HTTP request processing logic of NGINX Plus and NGINX Open Source, specifically affecting configurations that utilize the alias directive in conjunction with rewrite rules or logging directives that reference the $request_filename variable. This flaw represents a critical memory safety issue classified as CWE-120, Buffer Copy without Checking Size of Input (Classic Buffer Overflow), manifesting technically as a heap buffer overflow within the NGINX worker process. The vulnerability is triggered when an unauthenticated attacker sends specially crafted HTTP requests that exploit how NGINX handles path resolution and variable expansion in these specific configuration scenarios. While the exploitation requires certain conditions beyond the attacker's immediate control, such as specific server configurations or environmental factors, the ability to trigger this overflow remotely makes it a significant threat vector for both availability and confidentiality integrity of systems running affected versions of NGINX.
The operational impact of this vulnerability is twofold, encompassing both denial-of-service capabilities and potential remote code execution. In its most immediate form, the heap buffer overflow causes instability in the worker process, leading to an automatic restart or crash of the NGINX service. This results in a denial-of-service condition where legitimate users are unable to access services hosted behind the affected web server. However, the severity escalates significantly if the target system has Address Space Layout Randomization (ASLR) disabled or if the attacker possesses sufficient information to bypass ASLR protections. Under these conditions, the memory corruption can be leveraged to execute arbitrary code on the underlying operating system with the privileges of the NGINX worker process. This transforms a simple availability issue into a critical security breach allowing full system compromise, highlighting the importance of defense-in-depth strategies in server hardening.
From an attack perspective, this vulnerability aligns with ATT&CK technique T1498, Network Denial of Service, due to its capacity to disrupt service availability through process crashes. Furthermore, if exploited for code execution, it falls under techniques associated with initial exploitation and privilege escalation within the network environment. It is crucial to note that this issue is strictly a data plane vulnerability; there is no exposure in the control plane or management interface of NGINX. The attack surface is limited to HTTP traffic processed by the web server itself, meaning administrative interfaces remain unaffected unless they are exposed through the same vulnerable configuration context. This distinction helps security teams prioritize remediation efforts based on their specific deployment architectures and risk tolerance levels.
Mitigation strategies must focus primarily on upgrading to a patched version of NGINX that addresses this memory handling flaw. For organizations unable to immediately patch, temporary workarounds involve reviewing server configurations for the presence of alias directives combined with rewrite rules or access log formats that reference $request_filename. Modifying these configurations to avoid the specific interaction pattern that triggers the overflow can reduce risk until a permanent fix is applied. Additionally, ensuring that ASLR is enabled and functioning correctly on all systems running NGINX provides an essential layer of defense against code execution attempts derived from this vulnerability. Regular security audits and configuration reviews are recommended to identify similar risky patterns in web server setups, thereby strengthening the overall posture against memory corruption attacks.