Researchers have published a paper describing how a piece of malware planted on an air-gapped network can be controlled remotely using an office scanner and a light source, such as a laser or a smart bulb.
The method of using scanners to jump the air gap was first summarized back in 2014 at the Black Hat Europe conference by Adi Shamir, professor of Applied Mathematics at the Weizmann Institute of Science and one of the inventors of the RSA algorithm. Shamir along with Ben Nassi and Yuval Elovici of the Ben-Gurion University of the Negev in Israel have now published a detailed research paper on this attack method.
The experiments conducted by the experts show that an attacker can send commands to a piece of malware on an isolated machine by pointing a light source at a connected flatbed scanner that has its lid open from outside the building housing the device.
The malware can be programmed to initiate scans at a specified time and date when the attacker will start sending the commands. Researchers pointed out that only the first scan date needs to be set as subsequent dates can be supplied in each attack.
The commands are transmitted as pulses from a laser or a different light source – a 1 bit is transmitted when the light source is on, and a 0 bit is sent when it’s off. The light source can be a visible laser or an invisible infrared laser, which makes the attack stealthier. The light source can be attached to a stand or a drone.
The laser attack works if there is a clear line of sight from the outside of the building to the scanner. If the view is blocked by a curtain or a wall, the attacker can remotely hijack a smart bulb located in the same room as the targeted scanner and use it to send the signals.
When Shamir first mentioned the attack method, he only described a scenario involving a laser attached to a drone. In the paper they published now, the researchers also detailed an attack involving smart bulbs, which have been known to be vulnerable to remote hacking.
In their experiments, the experts flew a drone to the third floor of an office building at a distance of 15 meters (50 feet) from the scanner. Using a transmission rate of 50 milliseconds for each bit, they managed to send the command “d x.pdf,” which can be a command for deleting a file named “x.pdf,” in 3.2 seconds. A stronger laser allowed them to conduct a successful attack from 900 meters away (0.55 miles).
In the smart bulb attack scenario, which involves hijacking the bulb and commanding it to turn on and off to transmit 1 and 0 bits, instructions were sent to the malware from a car passing by the targeted building. In this experiment, researchers simulated a ransomware attack, where the threat actor sent four bytes of data in the form of a “en q” command (i.e. encrypt directory q). The attack was carried out in four seconds at a 100 millisecond transmission rate.
Researchers pointed out that this is a two-way communication channel as the malware can use the scanner itself to emit visible light pulses that can be captured and decoded by a video recorder mounted on a drone. Videos have been published to show both the laser and smart bulb attacks:
This is not the only method devised by researchers for jumping air gaps. Over the past months, they have detailed several techniques, including ones involving HDD activity LEDs, USB devices, the noise emitted by hard drives and fans, and heat emissions.