Researchers at the Fraunhofer Institute for Communication, Information Processing and Ergonomics investigated the possibilities of malware performing data transfer across the sound devices in air gapped computers. Air gapping is a security measure that involves removing a computer or network from any external network physically and also ensuring there is no wireless connection.
In the proof of concept exploit, the researchers were able to hijack the target computer’s sound card and speakers to transmit data to a receiver. The researchers’ most successful trial used software intended for underwater communication. An infected air gapped computer sent out the ultrasonic signal, which was picked up by the attackers’ receiving microphone up 65 feet away and demodulated by the software on the attack computer. While, contrary to rumor, the proof of concept did not actually infect via sound waves, it is theoretically possible.
The proof of concept exploit used conventional means, such as external drives, to infect the target system. Despite acoustic infection’s low bandwidth (20bits/s), the fact that it uses sound beyond the range of human hearing means that malware can stealthily send data without an Internet connection. That capacity is enough to enable sending small phrases picked out for their relevance, making the strongest password easily accessible to the attacker.
To prevent data exfiltration in sound-gapped computers, the researchers recommend that the audio devices be removed. Nevertheless, it’s still possible that a compromised computer could be outfitted with supplemental audio devices that are very difficult to detect.