Nohl and Lell, researchers for the security consultancy SR Labs, are hardly the first to point out that USB devices can store and spread malware. But the two hackers didn’t merely copy their own custom-coded infections into USB devices’ memory. They spent months reverse engineering the firmware that runs the basic communication functions of USB devices—the controller chips that allow the devices to communicate with a PC and let users move files on and off of them. Their central finding is that USB firmware, which exists in varying forms in all USB devices, can be reprogrammed to hide attack code. “You can give it to your IT security people, they scan it, delete some files, and give it back to you telling you it’s ‘clean,’” says Nohl. But unless the IT guy has the reverse engineering skills to find and analyze that firmware, “the cleaning process doesn’t even touch the files we’re talking about.”
The problem isn’t limited to thumb drives. All manner of USB devices from keyboards and mice to smartphones have firmware that can be reprogrammed—in addition to USB memory sticks, Nohl and Lell say they’ve also tested their attack on an Android handset plugged into a PC. And once a BadUSB-infected device is connected to a computer, Nohl and Lell describe a grab bag of evil tricks it can play. It can, for example, replace software being installed with with a corrupted or backdoored version. It can even impersonate a USB keyboard to suddenly start typing commands. “It can do whatever you can do with a keyboard, which is basically everything a computer does,” says Nohl.
The malware can silently hijack internet traffic too, changing a computer’s DNS settings to siphon traffic to any servers it pleases. Or if the code is planted on a phone or another device with an internet connection, it can act as a man-in-the-middle, secretly spying on communications as it relays them from the victim’s machine.
I’ve always behaved as though if anyone can get physical hold of my computer or device, they can crack it. I behave that way because it’s true. But this new threat can be piggybacked into any USB device, opening up avenues that were only open before if someone got physical hold of your stuff.
My advice? Don’t borrow any wired keyboard or mice. And if you use an Android phone or tablet, charge it on a wall charger, period — don’t plug it into your Windows or Mac computer.
image via shutterstock / Piti Tan