Cybersecurity“Surfing Attack” Hacks Siri, Google with Ultrasonic Waves

Ultrasonic waves don’t make a sound, but they can still activate Siri on your cellphone and have it make calls, take images or read the contents of a text to a stranger. All without the phone owner’s knowledge.

Attacks on cell phones aren’t new, and researchers have previously shown that ultrasonic waves can be used to deliver a single command through the air.

However, new research from Washington University in St. Louis expands the scope of vulnerability that ultrasonic waves pose to cellphone security. These waves, the researchers found, can propagate through many solid surfaces to activate voice recognition systems and — with the addition of some cheap hardware — the person initiating the attack can also hear the phone’s response.

The results were presented Feb. 24 at the Network and Distributed System Security Symposium in San Diego.

“We want to raise awareness of such a threat,” said Ning Zhang, assistant professor of computer science and engineering at the McKelvey School of Engineering. “I want everybody in the public to know this.”

Zhang and his co-authors were able to send “voice” commands to cellphones as they sat inconspicuously on a table, next to the owner. With the addition of a stealthily placed microphone, the researchers were able to communicate back and forth with the phone, ultimately controlling it from afar.

Ultrasonic waves are sound waves in a frequency that is higher than humans can hear. Cellphone microphones, however, can and do record these higher frequencies. “If you know how to play with the signals, you can manipulate them such that when the phone interprets the incoming sound waves, it will think that you are saying a command,” Zhang said.

WUSTL says that to test the ability of ultrasonic waves to transmit these “commands” through solid surfaces, the research team set up a host of experiments that included a phone on a table.

Attached to the bottom of the table was a microphone and a piezoelectric transducer (PZT), which is used to convert electricity into ultrasonic waves. On the other side of the table from the phone, ostensibly hidden from the phone’s user, is a waveform generator to generate the correct signals.