CVE-2016-4450 in nginx
Summary
by MITRE
os/unix/ngx_files.c in nginx before 1.10.1 and 1.11.x before 1.11.1 allows remote attackers to cause a denial of service (NULL pointer dereference and worker process crash) via a crafted request, involving writing a client request body to a temporary file.
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Analysis
by VulDB Data Team • 08/22/2022
The vulnerability identified as CVE-2016-4450 represents a critical denial of service weakness in the nginx web server software that affects versions prior to 1.10.1 and 1.11.x before 1.11.1. This flaw exists within the operating system specific file handling module located at os/unix/ngx_files.c, where the software fails to properly validate certain conditions when processing client requests that require temporary file creation. The issue manifests when nginx receives a specially crafted HTTP request that triggers the server to attempt writing the client request body to a temporary file, creating a scenario where a NULL pointer dereference occurs during the file I/O operation.
The technical implementation of this vulnerability stems from inadequate error handling within the file writing process that occurs when nginx processes client request bodies. When a request is received that causes the system to create a temporary file for storing the request body, the code path does not properly check whether the file descriptor or file handle has been successfully initialized before attempting to write to it. This results in a NULL pointer dereference that causes the worker process to crash immediately, effectively rendering the affected nginx process unavailable to handle further requests. The flaw is particularly dangerous because it can be triggered by any remote attacker who can send a malformed HTTP request to the server, requiring no authentication or privileged access.
The operational impact of this vulnerability extends beyond simple service disruption to potentially enable broader attack scenarios that align with the attacker's objectives. When a worker process crashes due to this NULL pointer dereference, the nginx server must restart the process to continue serving requests, which can lead to temporary unavailability of the web service. In high-traffic environments or when multiple processes are affected simultaneously, this vulnerability can result in cascading failures that significantly impact system availability and performance. The vulnerability also presents opportunities for attackers to conduct sustained denial of service attacks that can progressively degrade server performance or completely shut down the web service, particularly when combined with other attack vectors that can amplify the impact.
Mitigation strategies for CVE-2016-4450 should prioritize immediate software updates to versions 1.10.1 or 1.11.1 and later, which contain the necessary patches to address the NULL pointer dereference issue. Organizations should also implement network-level protections such as rate limiting and request filtering to reduce the impact of potential exploitation attempts. The vulnerability aligns with CWE-476 which describes NULL pointer dereference conditions, and can be categorized under ATT&CK technique T1499.004 for network denial of service attacks. Additionally, implementing proper input validation and robust error handling in the application code can help prevent similar issues in other software components. Security monitoring should include detection of unusual worker process restart patterns and abnormal request processing behavior that may indicate exploitation attempts. Organizations should also consider implementing redundant server configurations and load balancing strategies to minimize the impact of individual server failures caused by this vulnerability.