[SECURITY] Production Backend Exposed: CORS Misconfiguration Allows Any Origin to Access API

A critical security misconfiguration in a production backend server is actively exposing authenticated API endpoints to any website on the internet. The vulnerability stems from the use of an unconfigured CORS (Cross-Origin Resource Sharing) middleware, which, when deployed, permits cross-origin requests from any domain. This flaw effectively allows malicious or third-party sites to make requests to the backend API while leveraging the credentials and sessions of logged-in users, posing a severe data integrity and user privacy risk.

The bug is located in the `backend/src/index.js` file, where the line `app.use(cors())` is implemented without any origin restrictions. In a production environment, this configuration fails to enforce a basic security boundary, allowing the API to interact with scripts from any origin. The expected behavior is to restrict access exclusively to the official frontend domain and, for development purposes, to localhost. The issue provides a clear, reproducible path: deploying the current backend code to production and making a cross-origin request from an arbitrary domain will succeed without triggering a CORS error.

This oversight represents a fundamental application security failure, leaving user data and backend functionality vulnerable to cross-site request forgery (CSRF) and other client-side attacks. The provided fix guide outlines essential steps to remediate the vulnerability, including implementing a configured CORS middleware that reads allowed origins from an environment variable and adding integration tests to verify rejection of unauthorized requests. Until patched, the production system remains in a state of elevated risk, with its API surface area unnecessarily and dangerously broad.