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Study Reveals Inaudible Sound Attack Threatens Voice Assistants

by Abeerah Hashim
inaudible sound attack on voice assistant

A recent study reveals how attackers can trigger vulnerabilities in voice assistants for malicious purposes. As demonstrated, using inaudible sound trojans allows exploiting existing vulnerabilities in voice assistants to attack respective devices.

Inaudible Sound Can Attack Voice Assistants

A team of researchers from the University of Texas at San Antonio and the University of Colorado, Colorado Springs, devised an interesting attack strategy aimed at voice assistants.

Specifically, the researchers have developed NUIT (Near-Ultrasound Inaudible Trojan) attack that involves injecting malicious voice commands in the inaudible range to trigger voice assistants.

For this, the attacker may trick the victim into installing a malicious app that later meddles with the device’s voice assistants by playing audio files. Or, the attack may happen through a maliciously crafted website if and when the victim visits it, for instance, following a phishing attack.

Once done, the attacker exploits the device’s microphone with near-ultrasound waves inaudible to humans. And before performing any other action, it may even reduce the target device’s volume via a similar inaudible command so that the voice assistant’s response to the command won’t be heard. Thus, the victim user wouldn’t know the attack is happening while the adversary continues executing malicious commands.

The researchers have shared the following videos as demonstrations of the NUIT attack. In the first video, the attacker attacks an iPhone, triggering Siri to open the victim place’s main door with silent commands.

Likewise, in the following video, the attacker triggers Google Assistant (popular on Android devices) to do the same.

In both cases, the owner of the target device is sitting nearby the hacked device. Yet, the victim remains oblivious to its phone’s activities.

Limitations And Countermeasures

According to the researchers, NUIT attack isn’t as perfect as it seems. It mainly works for handsets bearing linear speaker and microphone. Since that’s now getting common, the researchers advise the device manufacturers to consider redesigning the placement so as to prevent inaudible sound transmission to the microphone.

While that’s a remedy for the future, for now, the researchers advise users to switch to using earphones instead of device speakers. That’s because earphones ensure a low transmission of sound, preventing direct commands to the microphone.

The researchers are going to present their study at the USENIX Security 2023 scheduled for August 9 and 11, 2023, at the Anaheim Marriott in Anaheim, CA, USA. Whereas details about the NUIT attack is also available on a dedicated webpage.

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