Compliance Impact

This vulnerability allows unauthenticated users to bypass middleware protections such as authentication, authorization, and input validation on protected routes. As a result, sensitive or restricted administrative endpoints may become accessible to unauthorized users, potentially leading to unauthorized access to personal or sensitive data. Such unauthorized access could lead to non-compliance with common standards and regulations like GDPR and HIPAA, which require strict access controls and protection of sensitive information. Therefore, exploitation of this vulnerability could negatively impact compliance with these regulations. [1]

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Detection Guidance

This vulnerability can be detected by testing if URL-encoded paths bypass middleware protections in your NestJS application using @nestjs/platform-fastify versions prior to 11.1.11. Specifically, you can send HTTP requests with URL-encoded characters in the path to routes protected by middleware (e.g., an admin route) and observe if the middleware is bypassed. For example, if your protected route is '/admin', try accessing '/%61dmin' (where '%61' is the URL-encoded 'a') and check if the request is allowed without authentication or authorization. A simple curl command to test this could be: curl -i -X GET http://yourserver/%61dmin. If the middleware is bypassed, the response will indicate access without proper checks. Similarly, you can test other routes with encoded characters. This approach helps detect the TOCTOU race condition causing middleware bypass. [1, 2]

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Executive Summary

This vulnerability affects NestJS applications using the @nestjs/platform-fastify package before version 11.1.11. It involves a Fastify URL encoding middleware bypass, where if the application uses NestMiddleware for security checks (like authentication or authorization) applied to specific routes via string paths or controllers, an attacker can bypass these middleware protections. This means unauthenticated users might access protected routes, restricted administrative endpoints could be accessed by lower-privileged users, and middleware that performs sanitization or validation might be skipped.

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Impact Analysis

The impact of this vulnerability includes unauthorized access to protected routes and administrative endpoints by unauthenticated or lower-privileged users. It can lead to security checks being bypassed, allowing attackers to perform actions they should not be permitted to do, potentially compromising the application's security and integrity.

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Mitigation Strategies

To mitigate this vulnerability, update the @nestjs/platform-fastify package to version 11.1.11 or later, where the Fastify URL encoding middleware bypass is patched. Additionally, review your application to avoid relying solely on NestMiddleware for security checks on specific routes using string paths or controllers, and consider applying security middleware globally or using alternative methods to enforce authentication and authorization.

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