‘Surfing attack’ hacks Siri, Google with ultrasonic waves

‘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 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 at the Network
and Distributed System Security Symposium in San Diego. The researchers were able to send “voice”
commands to cellphones as they sat 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. 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,
is a waveform generator to generate the correct signals. The team ran two tests, one to retrieve an
SMS (text) passcode and another to make a fraudulent call. The first test relied on the common virtual
assistant command “read my messages” and on the use of two-factor authentication, in
which a passcode is sent to a user’s phone — from a bank — to verify the user’s
identity. The attacker first told the virtual assistant
to turn the volume down to Level 3. At this volume, the victim did not notice
their phone’s responses in an office setting with a moderate noise level. Then, when a simulated message from a bank
arrived, the attack device sent the “read my messages” command to the phone. The response was audible to the microphone
under the table, but not to the victim. In the second test, the attack device sent
the message “call Sam with speakerphone,” initiating a call. Using the microphone under the table, the
attacker was able to carry on a conversation with “Sam.” The team tested 17 different phone models,
including popular iPhones, Galaxy and Moto models. All but two were vulnerable to ultrasonic
wave attacks. They also tested different table surfaces
and phone configurations. They did it on metal, glass and wood. They tried placing the phone in different
positions, changing the orientation of the microphone. They placed objects on the table in an attempt
to dampen the strength of the waves. It still worked. Even at distances as far as 30 feet. Ultrasonic wave attacks also worked on plastic
tables, but not as reliably. Phone cases only slightly affected the attack
success rates. Placing water on the table, potentially to
absorb the waves, had no effect. Moreover, an attack wave could simultaneously
affect more than one phone. The team suggested some defense mechanisms
that could protect against such an attack. One idea would be the development of phone
software that analyzes the received signal to discriminate between ultrasonic waves and
genuine human voices. Changing the layout of mobile phones, such
as the placement of the microphone, to dampen or suppress ultrasound waves could also stop
a surfing attack. But there’s a simple way to keep a phone
out of harm’s way of ultrasonic waves: the interlayer-based defense, which uses a soft,
woven fabric to increase the “impedance mismatch.” In other words, put the phone on a tablecloth.

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