The Walkie-Talkie app let two people who had accepted an invitation send and receive short audio messages.
But Apple said it had been “made aware” of a flaw that “could allow somebody to listen through another customer’s iPhone without consent”.
It has disabled the feature and apologised for the inconvenience.
However, Apple said it was not aware of the Walkie-Talkie bug being exploited by anybody in the real world.
It said “specific conditions and sequences of events” would be required to exploit the bug.
Apple found a similar “eavesdropping” flaw in its FaceTime video-calling app back in January.
In some cases, callers could activate the microphone on a target iPhone even if the recipient did not answer their call.