German bug hunter Linus Henze said he would not release details of the problem to Apple until it included MacOS in its bounty programme.
A FaceTime security update is available for the Mac version of the video messaging app as well.
The update that fixes the FaceTime flaw is called iOS 12.1.4 with Apple stating that it "provides important security updates and is recommended for all users". So, if you like group FaceTime calls, this update is a must-have for you (and those you called).
Although the FaceTime bug has now been addressed, its emergence is particularly embarrassing for Apple.
The bug enabled interlopers to turn an iPhone or iPad into a live microphone while using Group FaceTime. While they were fixing the bug, they disabled Group FaceTime, so that the bug could not be abused.
Apple initially said it would release updates to macOS and iOS addressing the flaw within a few days of its public disclosure.
Apple seems to limit the spread of older firmware on its iOS devices in an attempt to keep iPhone and iPad users secure.
Apple turned off the group-chat feature last week, after a 14-year-old boy in Tucson, Arizona, discovered the flaw.
This happened for as long as the call was ringing, and ended when the call was rejected or timed out.
While you may think that's due to a lower severity level for issues relating to the Live Photos feature in FaceTime, the iOS Foundation framework, and the I/O Kit framework, Twitter user Ben Hawkes claims two of these lesser-known vulnerabilities were in fact "exploited in the wild as 0day".
Your device will now download and install the update and restart your device. There's also an update for the Shortcuts app on iOS from Apple.
To download the latest version on your device, go to Settings General Software Update and then follow the on-screen instructions.