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/platform-fastify@11.1.11".