A team of cybersecurity researchers – Abhishek Anand, Chen Wang, JIan Liu, Nitesh Saxena, and Yingying Chen – have discovered and demonstrated a new side -channel attack that could potentially allow apps to listen in on the voice coming through an Android phone’s loudspeakers without requiring any device permissions.
This new attack has been named Spearphone. It works by taking advantage of the accelerometer built into most Android phones. An accelerometer is a sensor that can detect and monitor the movement of a phone, like being shaken, tilted, or lifted up. The accelerometer can be accessed by any app with any permissions.
According to The Hacker News, “Since the built-in loudspeaker of a smartphone is placed on the same surface as the embedded motion sensors, it produces surface-borne and aerial speech reverberations in the body of the smartphone when loudspeaker mode is enabled.” The nature of sound is vibrations that travel through a medium transferring energy to our ear drums which then translate the mechanical vibrations into electric signals which our brains translate into sounds. This attack bypasses the need for a second microphone replacing the audio receiver with the accelerometer in the phone itself to translate the soundwaves into electrical messages.
The researchers created and Android application that was designed to record speech reverberations using the accelerometer and send the captured data back to an attacker-controller server as a proof-of-concept. The researchers have shown that this attack can successfully be used to spy on phone calls, listen to voice notes or multimedia, and to spy on the use of an assistant such as Google Assistant or Bixby, as shown below.