Adversaries may capture audio to collect information by leveraging standard operating system APIs of a mobile device. Examples of audio information adversaries may target include user conversations, surroundings, phone calls, or other sensitive information. Android and iOS, by default, require that applications request device microphone access from the user.

On Android devices, applications must hold the RECORD_AUDIO permission to access the microphone or the CAPTURE_AUDIO_OUTPUT permission to access audio output. Because Android does not allow third-party applications to hold the CAPTURE_AUDIO_OUTPUT permission by default, only privileged applications, such as those distributed by Google or the device vendor, can access audio output. However, adversaries may be able to gain this access after successfully elevating their privileges.

With the CAPTURE_AUDIO_OUTPUT permission, adversaries may pass the MediaRecorder.AudioSource.VOICE_CALL constant to MediaRecorder.setAudioOutput, allowing capture of both voice call uplink and downlink. On iOS devices, applications must include the NSMicrophoneUsageDescription key in their Info.plist file to access the microphone.