https://9to5mac.com/2019/01/28/facetime-bug-hear-audio/
"A significant bug has been discovered in FaceTime and is currently spreading virally over social media. The bug lets you call anyone with FaceTime, and immediately hear the audio coming from their phone — before the person on the other end has accepted or rejected the incoming call.
Naturally, this poses a pretty privacy problem as you can essentially listen in on any iOS user, although it still rings like normal, so you can’t be 100% covert about it. Nevertheless, there is no indication on the recipient’s side that you could hear any of their audio.
9to5Mac has reproduced the FaceTime bug with an iPhone X calling an iPhone XR, but it is believed to affect any pair of iOS devices running iOS 12.1 or later.
Here’s how to do the iPhone FaceTime bug:
- Start a FaceTime Video call with an iPhone contact.
- Whilst the call is dialling, swipe up from the bottom of the screen and tap Add Person.
- Add your own phone number in the Add Person screen.
- You will then start a group FaceTime call including yourself and the audio of the person you originally called, even if they haven’t accepted the call yet.
It will look like in the UI like the other person has joined the group chat, but on their actual device it will still be ringing on the lockscreen."
This is quite a bug indeed. I wonder if they can disable this in the backend somehow?