Hackers Can Talk To Voice Assistants Like Siri And Alexa By Speaking With A Voice You Can't Hear


Imagine what might happen if someone with evil intent could talk to your voice controlled devices and you couldn’t hear them. Siri, Alexa, Cortana, the Google Assistant and more would follow their commands. They could take over your phone, your computer, your gaming console, your watch, your car or your hands-free voice assistant. Sound like trouble? It can happen.

The range of human hearing covers sound frequencies between 20 Hz and 20 kHz (20 to 20,000 cycles per second). Dogs can hear sounds above 20 kHz which is why they hear dog whistles when their owners don’t. The microphones that pick up human voices in voice-controlled devices can also register sounds above 20 kHz. And that’s a problem.

Sound wave of a human voice

Credit: CSTRSK/Pixabay

Researchers at Zhejiang University in Hangzhou have developed a method they call DolphinAttack that uses ultrasonic frequencies that lie above the range of human hearing to communicate with the voice recognition systems that power many popular voice assistants. The attacker speaks a command, DolphinAttack translates the command to the ultrasonic sound range, the inaudible command is sent to the user’s device, and the device responds.

How can an attacker send an inaudible command to a victim’s device? Portable attack systems powered by low-watt amplifiers can be used to access devices within relatively short ranges. The guy at the next table in a coffee shop could be speaking silently to your cell phone, watch or laptop. Inaudible commands can also be embedded in videos that are played at home. Any voice assistant in the room that can hear the video could be affected.

The researchers tested DolphinAttack against 16 devices running various versions of iOS, macOS, Android, Windows 10 and Amazon’s 5589. Siri, Alexa, Cortana and the Google Assistant all heard the inaudible voice commands. They also successfully tested attack commands in English, Chinese, German, French and Spanish.

Using Siri to hack an iPhone with DolphinAttack

Credit: Guoming Zhang/YouTube

Voice assistants like Amazon’s Echo or Google’s Assistant respond to anyone who speaks the wake-up phrase, but Apple’s Siri only responds to the voice of the user who trained it. Is Siri safe from DolphinAttack? No. The researchers communicated with Siri using two methods. If they had recordings of the owner’s voice, they sliced the recordings and constructed the “Hey Siri” wake up command from the samples. If they did not have recordings, they used a text-to-speech system to generate the wake-up command and then ran the output through software that varied tone and timbre. Siri responded when she heard a voice that was similar to the owner’s voice.

The researchers demonstrated the effectiveness of DolphinAttack by enticing Siri to initiate a FaceTime call on an iPhone, getting Google Now to switch a phone to airplane mode, and by manipulating the navigation system in an Audi. They also showed that DolphinAttack can be used to visit a malicious website that installs exploit kits on the victim’s computer, send fake emails, text messages and comments on a website, and enroll the victim’s device in a botnet.

Users can protect themselves from being victimized by inaudible voice commands by turning off the voice-activation function on their devices. The voice assistant would then have to be started manually after which it would respond to voice commands. A better solution would be if the makers of voice activated systems shifted to building devices that did not recognize audio signals above 20 kHz.

