A few weeks ago, security researcher Dragos Ruiu publicly claimed that computers in his lab were being infected by some sort of stealthy over-the-air transmission method that relied on ordinary speakers and microphones to transmit the malware payload from system to system. Ruiu nicknamed this bug “badBIOS,” and research into its existence (or lack thereof) continues. Multiple security researchers have lined up on both sides of the issue.
Now, however, there’s proof that at least one key aspect of badBIOS’ supposed design isn’t science fiction. Researchers have published a paper on how malware can be designed to cross the air gap by transmitting information through speakers and recording it via microphone. An air gap is a measure that boosts the security of a system by essentially isolating it from other, less secure networks. Rather than relying on TCP-IP, the research team used a network stack originally developed for underwater communication.
The signal was propogated through the use of a software-defined modem based on the GNU Radio project. They also tested with a mini-modem, but found the software-defined modem had better range characteristics. Line-of-site transfer speeds stretched up to 19.7m, and researchers were able to ping the signal back and forth across systems.