Stealthy Data Exfiltration Possible via Magnetic Fields

Researchers have demonstrated that a piece of malware present on an isolated computer can use magnetic fields to exfiltrate sensitive data, even if the targeted device is inside a Faraday cage.

A team of researchers at the Ben-Gurion University of the Negev in Israel have created two types of proof-of-concept (PoC) malware that use magnetic fields generated by a device’s CPU to stealthily transmit data.

A magnetic field is a force field created by moving electric charges (e.g. electric current flowing through a wire) and magnetic dipoles, and it exerts a force on other nearby moving charges and magnetic dipoles. The properties of a magnetic field are direction and strength.

The CPUs present in modern computers generate low frequency magnetic signals which, according to researchers, can be manipulated to transmit data over an air gap.

The attacker first needs to somehow plant a piece of malware on the air-gapped device from which they want to steal data. The Stuxnet attack and other incidents have shown that this task can be accomplished by a motivated attacker.

Once the malware is in place, it can collect small pieces of information, such as keystrokes, passwords and encryption keys, and send it to a nearby receiver.

The malware can manipulate the magnetic fields generated by the CPU by regulating its workload – for example, overloading the processor with calculations increases power consumption and generates a stronger magnetic field.

The collected data can be modulated using one of two schemes proposed by the researchers. Using on-off keying (OOK) modulation, an attacker can transmit “0” or “1” bits through the signal generated by the magnetic field – the presence of a signal represents a “1” bit and its absence a “0” bit.

Since the frequency of the signal can also be manipulated, the malware can use a specific frequency to transmit “1” bits and a different frequency to transmit “0” bits. This is known as binary frequency-shift keying (FSK) modulation.

Ben Gurion University researchers have developed two pieces of malware that rely on magnetic fields to exfiltrate data from an air-gapped device. One of them is called ODINI and it uses this method to transmit the data to a nearby magnetic sensor. The second piece of malware is named MAGNETO and it sends data to a smartphone, which typically have magnetometers for determining the device’s orientation.

In the case of ODINI, experts managed to achieve a maximum transfer rate of 40 bits/sec over a distance of 100 to 150 cm (3-5 feet). MAGNETO is less efficient, with a rate of only 0.2 – 5 bits/sec over a distance of up to 12.5 cm (5 inches). Since transmitting one character requires 8 bits, these methods can be efficient for stealing small pieces of sensitive information, such as passwords.

Researchers demonstrated that ODINI and MAGNETO also work if the targeted air-gapped device is inside a Faraday cage, an enclosure used to block electromagnetic fields, including Wi-Fi, Bluetooth, cellular and other wireless communications.

In the case of MAGNETO, the malware was able to transmit data even if the smartphone was placed inside a Faraday bag or if the phone was set to airplane mode.

Ben-Gurion researchers have found several ways of exfiltrating data from air-gapped networks, including through infrared cameras, router LEDs, scanners, HDD activity LEDs, USB devices, the noise emitted by hard drives and fans, and heat emissions.

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