https://phys.org/news/2019-01-facetime-eavesdropping-bug-disable-app.html

The bug, which USA TODAY reported on Monday, involved starting a FaceTime call, swiping up to add a person then entering your own phone number. The move starts a group call and automatically answers the call for the first person, enabling someone to listen in without their knowledge.

In a statement to USA TODAY, Apple said it is "aware of this issue and we have identified a fix that will be released in a software update later this week."