No matter how secure you think a computer is, there’s always a vulnerability somewhere that a remote attacker can utilize if they’re determined enough. To reduce the chance of sensitive material being stolen, many government and industrial computer systems are not connected to outside networks. This practice is called air-gapping, but even that might not be enough. The Stuxnet worm from several years ago spread to isolated networks via USB flash drives, and now researchers at Ben Gurion University in Israel have shown that it’s possible to rig up two-way communication with an air-gapped computer via heat exchange.
Researchers call this technique of harvesting sensitive data “BitWhisper.” It was developed and tested in a standard office environment with two systems sitting side-by-side on a desk. One computer was connected to the Internet, while the other had no connectivity. This setup is common in office environments where employees are required to carry out sensitive tasks on the air-gapped computer while using the connected one for online activities.
BitWhisper does require some planning to properly execute. Both the connected and air-gapped machines need to be infected with specially designed malware. For the Internet box, that’s not really a problem, but even the air-gapped system can be infected via USB drives, supply chain attacks, and so on. Once both systems are infected, the secure machine without Internet access can be instructed to generate heating patterns by ramping up the CPU or GPU. The internet-connected computer sitting nearby can monitor temperature fluctuations using its internal sensors and interpret them as a data stream. Commands can also be sent from the Internet side to the air-gapped system via heat.