Nest has a Fastify URL Encoding Middleware Bypass (TOCTOU)
A NestJS application is vulnerable if it meets all of the following criteria: Platform: Uses @nestjs/platform-fastify. Security Mechanism: Relies on NestMiddleware (via MiddlewareConsumer) for security checks (authentication, authorization, etc.), or through app.use() Routing: Applies middleware to specific routes using string paths or controllers (e.g., .forRoutes('admin')). Example Vulnerable Config: // app.module.ts export class AppModule implements NestModule { configure(consumer: MiddlewareConsumer) { consumer .apply(AuthMiddleware) // Security check .forRoutes('admin'); // Vulnerable: Path-based restriction } …