Nest is a framework for building scalable Node.js server-side applications. Versions prior to 11.1.11 have a Fastify URL encoding middleware bypass. A NestJS application is vulnerable if it uses @nestjs/platform-fastify.

relies on NestMiddleware (via MiddlewareConsumer) for security checks (authentication, authorization, etc.), or through app.use().

and applies middleware to specific routes using string paths or controllers (e.g., .forRoutes('admin')). Exploitation can result in unauthenticated users accessing protected routes, restricted administrative endpoints becoming accessible to lower-privileged users, and/or middleware performing sanitization or validation being skipped. This issue is patched in @nestjs/[email protected].