Disconnecting a computer from all networks is no longer a foolproof way to make sure that it will no longer communicate to other systems, according to research that will be presented at the USENIX Security 2015 Conference in August.
Researchers from Ben-Gurion University of the Negev were able to create programs to infect a computer and a mobile device and could then transmit data between the two systems by turning the computer system into an antenna that could send data on the frequencies cellular devices use. Dubbed GSMem, the malicious code has a small memory footprint, works on Windows and Linux systems, and can send data up to 90 feet.
"Once a compromised mobile phone is in the vicinity of the desktop computer, it can monitor and receive transmitted data," Mordechai Guri, the primary researcher and a Ph.D. candidate in BGU's Department of Information Systems Engineering, told eWEEK in an email. "PIN and passwords can be successfully recognized."
High-security environments, common in intelligence agencies and military bases, frequently use air-gapped systems to dramatically reduce exposure to malicious software and attempts at espionage. Air-gapped systems are not hack-proof, however. In 2008, an infected USB drive inserted into an air-gapped system led to a massive compromise and the theft of terabytes of sensitive and classified data. In 2009, the Stuxnet attack also hitched a ride on a USB memory sticks to infect systems inside an Iranian nuclear refinement facility.
The Israeli research has focused on ways to go beyond hand-carried drives as ways to sneak out data from secure facilities. Earlier research, called BitWhisper, used heat between two nearby computers to communicate data. Another effort, Air-Hopper, turned one computer into an FM radio to send data.
"Phones are often otherwise allowed in the vicinity of air-gapped computers thought to be secure," Guri said in a statement announcing the research. "Since modern computers emit some electromagnetic radiation (EMR) at various wavelengths and strengths, and cellular phones easily receive them, this creates an opportunity for attackers."
In a video posted on YouTube, the researchers showed a four-digit PIN being stolen from a computer and transmitted to a nearby feature phone. Older phones, like the one in the video, can only receive data at the glacial rate of 1 to 2 bits per second, Guri told eWEEK. Dedicated hardware could reach 100 bits per second, he said.
To defend against these attacks, security professionals should use a "zone" defense and define areas, or zones, in which phones and other devices are not allowed. In addition, using EM absorbing materials in walls could help reduce the range at which the attack is effective. Finally, technologies that look for anomalous signals in the vicinity could help detect when an attack is taking place, the researchers said.