Researchers at Ben-Gurion University of the Negev Cyber Security Research Center have created malware, called Fansmitter, that can hack an air-gapped computer by manipulating the speed of its CPU and chassis cooling fan to create sound signals that are picked up by a smartphone's microphone.
Creating a scenario where this hack can work requires several prerequisite steps, the researchers wrote. Essentially what is done is the malware sets up the computer's fan to act like a transmitter, while the smartphone acts as a receiver. The researchers said the air-gapped target computer first has to be physically compromised. They cited the Stuxnet attack – when a USB drive was reportedly used to deploy the malware that then attacked machinery at an Iranian nuclear facility – as one example of how this could be accomplished.
The smartphone must also be hacked prior to the attack enabling it to receive the data. In addition, it must be located within 24 feet of the target computer.
The computer then gathers the desired data which is modulated and transmitted using the acoustic sound waves emitted from the computer's cooling fan, created by running it faster or slower. This information is “heard” by the hacked smartphone, decoded and transmitted to the hacker.
“We show that software can regulate the internal fan's speed in order to control the acoustic waveform emitted from a computer,” the report said. "Binary data can be modulated and transmitted over these audio signals to a remote microphone."
The process is time-consuming with the fan only able to transmit the data at 15 bits per minute.
Fansmitter was successfully tested in a normal work environment with ambient background noises being generated by an air conditioning system, several other computer workstations and people.