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USB Device Firmware Can Be Reprogrammed to Hide Sophisticated Malware

Researchers Develop “BadUSB” to Demonstrate Extreme Threats Posed by USB Devices

Users have long been warned about the dangers of using USB drives, but new research shows significant threats that stem from USB devices that go far beyond thumb drives.

Most security solutions can easily identify and neutralize a piece of malware that's found on a USB device, but things get complicated if the threat resides directly in the firmware of such devices.

Dangers of USB Devices and Flash DrivesAt the upcoming Black Hat security conference, Karsten Nohl and Jakob Lell, both researchers at Germany-based SRLabs, will present a new type of malware which leverages the fact that the firmware found in thumb drives and other USB devices can be reprogrammed and abused for malicious purposes.

The problem, according to the researchers, is that the USB controller chips in peripherals can be reprogrammed to spoof other devices and there's little or no protection to prevent anyone from doing so. In order to demonstrate their findings, Nohl and Lell have developed BadUSB, a self-replicating piece of malware that can be used by an attacker to take control of a computer.

For instance, the BadUSB malware can make a device emulate a keyboard and use it to send commands on behalf of the victim. Attackers can steal data, install other pieces of malware, and even infect the controller chips of other USB devices connected to the affected computer, SRLabs said in a blog post.

USB devices can also be reprogrammed to spoof a network card, allowing the attackers to change the infected computer's DNS settings in an effort to redirect traffic. Thumb drives or external hard disks can be configured to detect when a computer is starting, and load a small virus into the operating system before boot. All of these scenarios will be demonstrated by the researchers at the Black Hat conference.

Nohl told SecurityWeek that they've implemented their attacks on one type of USB2 chip, one type of USB3 chip, and on Android phones. The controller chip firmware on which they've conducted their tests is very widespread and it's used in the thumb drives produced by various companies, the researcher explained.

"Any device connected over USB could become a BadUSB by re-programming its USB controller. Whether and how that is possible differs by controller chip," Nohl said via email.

According to Nohl, SRLabs spent three months on reverse engineering and reprogramming the two USB controller chips on which they have conducted experiments.

These types of threats are not detected by security solutions because malware scanners can't access the firmware running on USB devices. Behavior-based scanners aren't efficient either because devices infected with BadUSB don't exhibit any suspicious behavior. Instead, when the malware changes the functionality of a drive, it simply looks like the user plugged in a new device.

"To make matters worse, cleanup after an incident is hard: Simply reinstalling the operating system – the standard response to otherwise ineradicable malware – does not address BadUSB infections at their root. The USB thumb drive, from which the operating system is reinstalled, may already be infected, as may the hardwired webcam or other USB components inside the computer. A BadUSB device may even have replaced the computer’s BIOS – again by emulating a keyboard and unlocking a hidden file on the USB thumb drive," SRLabs explained in its blog post. "Once infected, computers and their USB peripherals can never be trusted again."

These attack techniques might seem new, but it's possible that they've already been leveraged in the wild. Documents leaked by former NSA contractor Edward Snowden in December 2013 show that the intelligence agency has been using similar methods in its surveillance operations.

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Eduard Kovacs (@EduardKovacs) is a contributing editor at SecurityWeek. He worked as a high school IT teacher for two years before starting a career in journalism as Softpedia’s security news reporter. Eduard holds a bachelor’s degree in industrial informatics and a master’s degree in computer techniques applied in electrical engineering.