Hard Drive Noise Allows Data Theft From Air-Gapped Computers

Researchers have identified yet another attack method that can be used to silently exfiltrate data from air-gapped computers. The latest technique involves the noise emitted by hard disk drives and it’s relatively efficient over short distances.

A team of experts from the Cyber Security Research Center at Ben-Gurion University of the Negev in Israel have published a research paper that details a method they call “DiskFiltration.”

Air-gapping a computer (i.e. isolating it from the Internet) is considered by many organizations a highly efficient security measure since, in theory, it should be impossible to remotely steal information from the device. However, researchers demonstrated on several occasions over the past years that the air-gap can be jumped using optic, thermal, electromagnetic and acoustic channels.

Since experts have shown that speakers and microphones connected to a computer can be leveraged for a two-way communications channel, many organizations have decided to ban employees from connecting such devices to air-gapped systems. However, there are other components that can be used for covert data exfiltration via acoustic signals.

In June, researchers from Ben-Gurion University of the Negev detailed Fansmitter, a method that involves using the noise from a device’s fans to send bits of data to a nearby receiver (e.g. mobile phone).

The new method, DiskFiltration, leverages the noise emitted by hard disk drives (HDD) and solid state hard drives (SSHD). More precisely, the noise is generated by the mechanical movement of the actuator arm over the platter that stores the data.

A piece of malware planted by attackers on the targeted air-gapped computer can conduct seek operations, which causes the actuator arm to move between different tracks. Starting and stopping a sequence of seek operations can be translated into zeros and ones, which represent bits of data.

The attacker can then place a smartphone, a smartwatch or a laptop near the infected device and pick up the emitted signals. In their experiments, researchers managed to obtain a 180 bits per minute (10,800 bits per hour) transfer rate over a two-meter (six feet) distance. The researchers conducted their experiments on both external and internal HDDs from Seagate and WD.

It’s worth noting that since solid state drives (SSD) store data on flash memory chips, they don’t have mechanical parts that can be used for such an attack. It’s also worth pointing out that the hard drive’s motor also produces acoustic noise, but it’s not relevant for such attacks as the rotation speed cannot be controlled via software.

In the past, the same group of researchers demonstrated similar attacks involving cellular frequencies, heat emissions, and electromagnetic signals emitted by the graphics card.

Experts said such attack methods could also be useful for exfiltrating data from environments where the Internet connection is heavily monitored and IDS/IPS systems would likely detect attempts to exfiltrate information.

Related: Air Gap or Not, Why ICS/SCADA Networks Are at Risk