https://www.vox.com/the-goods/2019/1/29/18202057/apple-facetime-bug-how-to-fix-video-eavesdrop

Apple says a solve will be pushed out this week.

As reported by 9to5Mac on Monday evening, a bug in Apple’s FaceTime app is currently allowing callers to listen through iPhone microphones before the call’s recipient even picks up. Further, if the recipient hits the power or volume button to reject the call, it will start transmitting video as well.