Signal: Incoming call can be connected without user interaction
There is a logic error in Signal that can cause an incoming call to be answered even if the callee does not pick it up.
In the Android client, there is a method handleCallConnected that causes the call to finish connecting. During normal use, it is called in two situations: when callee device accepts the call when the user selects 'accept', and when the caller device receives an incoming "connect" message indicating that the callee has accepted the call. Using a modified client, it is possible to send the "connect" message to a callee device when an incoming call is in progress, but has not yet been accepted by the user. This causes the call to be answered, even though the user has not interacted with the device. The connected call will only be an audio call, as the user needs to manually enable video in all calls.
The iOS client has a similar logical problem, but the call is not completed due to an error in the UI caused by the unexpected sequence of states. I would recommend improving the logic in both clients, as it is possible the UI problem doesn't occur in all situations.
