USB snooping made easy: crosstalk leakage attacks on USB hubs

Abstract

The Universal Serial Bus (USB) is the most prominent interface for connecting peripheral devices to computers. USB-connected input devices, such as keyboards, card-swipers and fingerprint readers, often send sensitive information to the computer. As such information is only sent along the communication path from the device to the computer, it was hitherto thought to be protected from potentially compromised devices outside this path. We have tested over 50 different computers and external hubs and found that over 90% of them suffer from a crosstalk leakage effect that allows malicious peripheral devices located off the communication path to capture and observe sensitive USB traffic. We also show that in many cases this crosstalk leakage can be observed on the USB power lines, thus defeating a common USB isolation countermeasure of using a charge-only USB cable which physically disconnects the USB data lines. Demonstrating the attack’s low costs and ease of concealment, we modify a novelty USB lamp to implement an off-path attack which captures and exfiltrates USB traffic when connected to a vulnerable internal or a external USB hub.