Signal: Incoming call can be connected without user interaction

People need to know when to update. Disclosure provides an incentive to do so, especially in corporate eenvironments.

Hackers on the other hand don't need to be informed, they can always look for juicy bugs the moment fixes are rolled out.

The bug tracker requires javascript, transcript for anyone that doesn't want to enable it:

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.

To reproduce this problem on the Android client, replace the method handleSetMuteAudio in the file WebRtcCallService.java with the following method.

  private void handleSetMuteAudio(Intent intent) {

    Log.e(TAG, "SENDING MESSAGE");

    this.dataChannel.send(new DataChannel.Buffer(ByteBuffer.wrap(Data.newBuilder().setConnected(Connected.newBuilder().setId(this.callId)).build().toByteArray()), false));

     intent.putExtra(EXTRA_CALL_ID, this.callId);
     intent.putExtra(EXTRA_REMOTE_ADDRESS, recipient.getAddress());
     handleCallConnected(intent);
  }

Then build the client and install it and make a call. When the call is ringing, the audio mute button can be pressed to force the callee device to connect, and audio from the callee device will be audible.

This bug is subject to a 90 day disclosure deadline. After 90 days elapse or a patch has been made broadly available (whichever is earlier), the bug report will become visible to the public.

Thank you, why absolutely no text can be displayed without JS enabled is beyond me. The page source is filled to the brim with trackers.

I think open-source software is great as well, but assuming these kind of bugs are found because you can inspect the code is very wishful thinking that doesn't always hold up.

This specific example required a Google department to find it. Who would have found it if Google got restrained by the NSA?. Other notable examples include openSSL.

On top of that, here is a great talk about how easy it would be to infiltrate open source projects: https://www.youtube.com/watch?v=fwcl17Q0bpk

> The page source is filled to the brim with trackers.

I would expect nothing less from a site owned by google.