Origin Validation Error

Summary

When a user-configured proxy on webpack-dev-server has a broad context (e.g. /) and "ws: true", it also intercepts the dev server's own HMR WebSocket and forwards it to the proxy target. This leaks the browser's cookies and Origin header to the backend, bypasses the dev server's Host/Origin validation, and corrupts the HMR socket (both HMR and the proxy end up writing to the same socket). Fixed in [email protected]. Workarounds: Scope user-defined proxy "context" to specific paths instead of "/", or omit "ws: true" from the proxy entry when WebSocket forwarding is not required.