The bug enabled interlopers to turn an iPhone into a live microphone while using Group FaceTime. Callers were able to activate another person's microphone remotely even before the person has accepted or rejected the call.
The teenager, Grant Thompson, and his mother said they unsuccessfully tried to contact the company about the problem for more than a week. Apple has been criticized for the delay in responding and has promised to improve procedures.
The FaceTime repair is included in the latest version of Apple's iOS 12 system, which became available to install Thursday.
Apple credited Thompson for discovering the FaceTime bug as part of its software update, nearly a week after thanking him for reporting the bug in the first place.