Next.js is a React framework for building full-stack web applications. Starting in version 16.0.1 and prior to version 16.1.7, in next dev, cross-site protection for internal websocket endpoints could treat Origin: null as a bypass case even if allowedDevOrigins is configured, allowing privacy-sensitive/opaque contexts (for example sandboxed documents) to connect unexpectedly. If a dev server is reachable from attacker-controlled content, an attacker may be able to connect to the HMR websocket channel and interact with dev websocket traffic. This affects development mode only. Apps without a configured allowedDevOrigins still allow connections from any origin. The issue is fixed in version 16.1.7 by validating Origin: null through the same cross-site origin-allowance checks used for other origins. If upgrading is not immediately possible, do not expose next dev to untrusted networks and/or block websocket upgrades to /_next/webpack-hmr when Origin is null at the proxy.
Weakness
The product uses a WebSocket, but it does not properly verify that the source of data or communication is valid.
Extended Description
WebSockets provide a bi-directional low latency communication (near real-time) between a client and a server. WebSockets are different than HTTP in that the connections are long-lived, as the channel will remain open until the client or the server is ready to send the message, whereas in HTTP, once the response occurs (which typically happens immediately), the transaction completes. A WebSocket can leverage the existing HTTP protocol over ports 80 and 443, but it is not limited to HTTP. WebSockets can make cross-origin requests that are not restricted by browser-based protection mechanisms such as the Same Origin Policy (SOP) or Cross-Origin Resource Sharing (CORS). Without explicit origin validation, this makes CSRF attacks more powerful.