The bug could be exploited to listen via the microphone of the person you are calling and possibly see video from their device before the person even picks up.
The flaw was exploited by adding yourself to a FaceTime call before the person on the other end picks up, by swiping up from the bottom of the screen before the call is answered and adding yourself to the call. That fooled FaceTime into thinking that the call was active, forcing the camera and microphone of the person you were calling to send data.
