Project Zero white-hat hacker Natalie Silvanovich discovered a logical flaw in the Signal messaging app for Android that could be exploited by a malicious caller to force a call to be answered at the receivers end without requiring his interaction. Signal vulnerability can only be exploited if the receiver fails to answer an audio call over Signal, forcing the incoming call to be automatically answered on the receiver’s device. The iOS client is affected by a similar logical issue, but the call is not established due to an error in the UI caused by a sequence of states.”]
Source: https://securityaffairs.co/wordpress/92159/hacking/bug-signal-android.html