GHSA-cxf3-9h37-7rr8: Echo: Rejected WebSocket upgrades can bypass Echo route-level access controls

Echo’s Proxy middleware selected a raw tunnel when the client requested a WebSocket upgrade, before validating whether the configured upstream accepted it. If the upstream returned an ordinary HTTP response and kept the connection alive, subsequent HTTP requests on that connection were forwarded directly to the same upstream without passing through Echo’s router or route-specific middleware.

This can bypass authentication or authorization enforced only at Echo’s routes. Exploitation requires an accessible proxy route, an upstream that rejects the upgrade without closing the connection, and a target resource on that upstream without independent authorization. The issue does not provide arbitrary-host proxying or bypass the upstream’s own authentication.