djust authentication bypass: a login_required / on_mount LiveView mount redirect does not close the WebSocket, allowing an unauthenticated client to dispatch event-handler calls

Impact

djust's LiveViewConsumer mounts a LiveView over a WebSocket. When a view is gated (login_required / permission_required, or an on_mount hook that returns a redirect) and the connecting user is not authorized, the consumer sent the client a {"type":"navigate","to":...} redirect frame and then returned — without closing the socket and without clearing self.view_instance. Only the PermissionDenied branch closed the connection (close(4403)).

A real browser obeys the navigate frame and leaves, hiding the problem. A raw WebSocket client that ignores the redirect keeps an open, mounted socket. Because handle_event did not re-check authentication/authorization after mount, that client could then send {"type":"event", ...} frames and invoke any @event_handler method on the gated view with no authenticated session — an authentication bypass on the live mutation path.

Who is affected: apps that expose LiveViews gated by login_required / permission_required / a redirecting on_mount hook, where the gated view's event handlers perform sensitive reads or mutations and do not independently re-verify the user. Exploitation requires a non-browser WebSocket client and knowledge (or enumeration) of the view path and event names.

Patches

Fixed in djust 1.0.4 (commit 1ae8aa9, PR #1780). Both the auth-redirect and on_mount-hook-redirect branches of handle_mount now send the navigate frame and then close(code=4403) and clear self.view_instance, mirroring the existing PermissionDenied branch. Public / authorized mounts are unchanged. The same path is reachable via handle_live_redirect_mount (which delegates to handle_mount) and is covered by the same fix.

1.0.4 also adds an opt-in defense-in-depth control, LIVEVIEW_CONFIG['reauth_on_event'] = True (default OFF), which re-resolves the user from the session and re-runs the view's auth check on every event for gated views.

Workarounds

Upgrade to 1.0.4. If you cannot upgrade immediately, on affected versions ensure that every @event_handler on a gated LiveView independently verifies the request user is authenticated and authorized (e.g. check request.user.is_authenticated / permissions at the top of each handler), since the framework does not re-check after mount on < 1.0.4. Alternatively, override the consumer's handle_mount to await self.close(code=4403) after emitting an auth redirect.

Proof of concept

Using Channels' WebsocketCommunicator against LiveViewConsumer.as_asgi() with an anonymous scope, mount a login_required view: the server emits a navigate frame but the socket stays open. Sending a subsequent {"type":"event", "handler":"<mutating_handler>", ...} frame reaches the handler and executes it without an authenticated session. On 1.0.4 the socket is closed with code 4403 immediately after the redirect and the event frame is rejected. (Regression test: tests/test_ws_auth_close_socket.py.)

Credits

Discovered internally during the djust v1.1.0 WebSocket-auth security review.