CVE-2026-97205: 
NGINX vulnerability analysis and mitigation

CVE-2026-97205 is a Use-After-Free (UAF) vulnerability in the ngx_http_core_module module of NGINX Plus and NGINX Open Source. When asynchronous file I/O (AIO) is enabled, processing Server Side Includes (SSI) pages containing include virtual commands can trigger a UAF in the NGINX worker process, potentially leading to memory corruption, worker crashes, or remote code execution. Affected versions include NGINX Open Source 1.30.0–1.30.5 and 1.31.0–1.31.6, and NGINX Plus R33–R36, 37.0.0–37.0.5, and 37.1.0. The vulnerability was published on October 14, 2026, and carries a CVSS v3.1 score of 8.1 (High) and a CVSS v4.0 score of 9.2 (Critical) (GitHub Advisory, F5 Advisory).

The root cause is a Use-After-Free condition (CWE-416) in NGINX's ngx_http_core_module. The flaw is triggered when asynchronous file I/O (AIO) is enabled and the server processes SSI pages that include include virtual directives — a specific configuration combination that causes the worker process to reference already-freed memory. Exploitation requires no authentication and no user interaction, but does require high attack complexity, as successful code execution is conditional on ASLR being disabled or the attacker being able to bypass it. This is a data plane issue only, with no control plane exposure (GitHub Advisory, F5 Advisory).

Successful exploitation can cause NGINX worker process crashes (denial of service), memory corruption, or arbitrary code execution on the affected server. Code execution is most feasible on systems where ASLR is disabled or can be bypassed; otherwise, the primary impact is DoS and memory corruption. All three security pillars — confidentiality, integrity, and availability — are rated High in the CVSS scoring, reflecting the potential for full compromise of the vulnerable NGINX instance (GitHub Advisory, F5 Advisory).

As of the disclosure date (October 14, 2026), there is no public proof-of-concept exploit and no evidence of in-the-wild exploitation. The vulnerability has not been added to the CISA Known Exploited Vulnerabilities (KEV) catalog. Exploitation requires a specific configuration (AIO enabled with SSI processing active) and is further constrained by the need to bypass or have ASLR disabled for code execution, increasing the practical difficulty (GitHub Advisory).

1. Reconnaissance: Identify internet-facing NGINX servers running vulnerable versions (Open Source 1.30.0–1.30.5 or 1.31.0–1.31.6; Plus R33–R36, 37.0.0–37.0.5, 37.1.0) using tools like Shodan or Censys, looking for NGINX version banners.
2. Identify SSI-enabled endpoints: Probe the target for SSI-enabled pages (typically .shtml extensions or pages returning SSI-processed content) to confirm the vulnerable configuration is active.
3. Confirm AIO configuration: Determine whether asynchronous file I/O is enabled on the target (e.g., via server behavior or configuration leaks), as this is a prerequisite for triggering the UAF.
4. Craft malicious SSI request: Send an HTTP request to an SSI-enabled endpoint with a specially crafted include virtual directive designed to trigger the use-after-free condition in the NGINX worker process.
5. Trigger UAF: The crafted request causes the worker process to reference freed memory, resulting in a crash (DoS) or memory corruption.
6. Achieve code execution (if ASLR disabled): On systems without ASLR, leverage the memory corruption to redirect execution flow and execute arbitrary code as the NGINX worker process user (GitHub Advisory, F5 Advisory).

• Logs: Repeated NGINX worker process crash entries in system logs (/var/log/nginx/error.log) such as worker process XXXX exited on signal 11 (SIGSEGV) or similar segmentation fault messages; unusual volume of requests to SSI-enabled endpoints (.shtml pages).
• Process: Unexpected NGINX worker process restarts or crashes; the master process repeatedly spawning new worker processes in a short timeframe.
• Network: High volume of HTTP requests targeting SSI-enabled pages from a single or small set of source IPs, particularly with unusual or malformed include virtual payloads in request bodies or parameters.
• File System: Unexpected files written to directories accessible by the NGINX worker process user, which may indicate successful code execution post-exploitation.

F5 has released patched versions: NGINX Open Source 1.30.6 (for the 1.30.x branch) and 1.31.7 (for the 1.31.x branch); NGINX Plus 37.0.5.1 (for the 37.0.x branch) and 37.1.0.1 (for the 37.1.x branch). As temporary workarounds, administrators should disable SSI processing or disable asynchronous file I/O (AIO) if not operationally required. Additionally, ensuring ASLR is enabled on all systems running NGINX significantly increases the difficulty of achieving code execution. Upgrading to a patched version is the recommended long-term remediation (F5 Advisory, GitHub Advisory).

Security news outlets including SecurityOnline and CyberSecurityNews covered the disclosure as part of a broader NGINX patch release addressing multiple vulnerabilities (SecurityOnline, CyberSecurityNews). Community discussion was noted on Mastodon via the DailyCyberSecurity and Threadlinqs accounts. LinuxCompatible reported that the NGINX 1.31.7 and 1.30.6 releases patched five security flaws, including two dating back to 2009 (LinuxCompatible).