Air-gapping, one of the simplest yet strongest defenses against network-borne threats, can be defeated, researchers have found. One of the key weapons in the attack is something just as simple: heat.

Air gapping is a security technique that has long been used to physically separate systems containing particularly sensitive data from the rest of the network. Many consider such device and network isolation to be one of the most effective ways of protecting computers from network borne threats.

Researchers from the Cyber Security Research Center at Israel’s Ben-Gurion University (BGU) have shown how even two air-gapped systems can be breached using heat and their in-built thermal sensors to establish a covert communication channel between them.

The method, dubbed BitWhisper, is part of ongoing research on air gap security at Ben-Gurion University. Last August, security researchers at the university demonstrated another method called AirHopper, in which they showed how it is possible for someone to surreptitiously extract data from a system using FM waves.

What makes BitWhisper different from other air gap research is the fact that this is the first time that researchers have been able to establish a bi-directional communication channel between two air-gapped systems, says Dudu Mimran, chief technology officer at BGU. Also important is the fact the method that was demonstrated does not involve the use of specialized hardware or peripherals.

“We created a way for two computers to communicate using heat,” Mimran says. “What we wanted to prove was that even though there might be an air gap between systems, they can be breached.”

There are some caveats to keep in mind, Mimran notes. For the method to be effective, the air-gapped computers have to be in close proximity to each other. The computers used to demonstrate BitWhisper for instance, were separated by just 15 inches.

Both computers also had specialized malware installed on them that was capable of hooking into the thermal sensors on the systems and also of increasing the heat generated by the computers in a controlled manner, Mimran says.

Importantly, the heat-based communication protocol demonstrated by the researchers supports a data transfer rate of a mere 8-bits per hour. So the method is unlikely of much use for stealing data in volume from air-gapped systems, he says. But it is an effective way to hack into an air-gapped network, transmit commands to it, and to steal passwords, secret keys, and similar data.

BitWhisper can also enable attackers to remotely command and control an air-gapped system, Mimran says.

In a soon-to-be-released paper on using thermal manipulations to breach air-gapped systems, BGU researchers describe BitWhisper as a method for establishing a covert channel between two systems by emitting heat from one system to the other in a controlled manner.

“By regulating the heating patterns, binary data is modulated into thermal signals,” the paper noted. “In turn, the adjacent PC uses its built-in thermal sensors to measure the environmental changes. These changes are then sampled, processed, and demodulated into binary data,” the researchers noted.

Once a bridging attempt is successful, a logical link can be established between the air-gapped internal system and the public network. “At this stage, the attacker can communicate with the formerly isolated network, issuing commands and receiving responses."

One of the biggest challenges in pulling this off is manipulating the heat generated by one computer in a controlled manner so that the other computer detects and responds in an appropriate manner to the change, Mimran says. The trick lies in figuring out how to differentiate between heat based on normal activity and heat generated by malicious activity.

“It is the first time we have communicated between two computers using heat,” he says.

Attacks that leverage BitWhipser and similar methods require a very high-degree of sophistication, Mimran says. So it is unlikely that the research will trigger a new wave of attacks against air-gapped systems. “Even for us, creating something that is robust and not just a simple example requires quite a bit of work,” he says.