USB devices offer hackers direct route into computers

USB devices such as keyboards, thumb drives and mice can be used to hack into personal computers in a potential new class of attacks that evade all known security protections, a top researcher revealed today.

Karsten Nohl, chief scientist with Berlin's SR Labs, noted that hackers could load malicious software onto tiny, low-cost computer chips that control functions of USB devices but which have no built-in shields against tampering with their code.

"You cannot tell where the virus came from. It is almost like a magic trick," said Nohl, whose research firm is known for uncovering major flaws in mobile phone technology.

The finding shows that bugs in software used to run tiny electronics components that are invisible to the average computer user can be extremely dangerous when hackers figure out how to exploit them. Security researchers have increasingly turned their attention to uncovering such flaws.

Nohl said his firm has performed attacks by writing malicious code onto USB control chips used in thumb drives and smartphones. Once the USB device is attached to a computer, the malicious software can log keystrokes, spy on communications and destroy data, he said.

Computers do not detect the infections when tainted devices are inserted because anti-virus programs are only designed to scan for software written onto memory and do not scan the firmware that controls the functioning of those devices, he said.

Nohl and Jakob Lell, a security researcher at SR Labs, will describe their attack method at next week's Black Hat hacking conference in Las Vegas.

Nohl said he would not be surprised if intelligence agencies, like the US National Security Agency, have already figured out how to launch attacks using this technique.

Last year, he presented research at Black Hat on breakthrough methods for remotely attacking SIM cards on mobile phones. In December, documents leaked by former NSA contractor Edward Snowden demonstrated that the US spy agency was using a similar technique for surveillance, which it called "Monkey Calendar."

An NSA spokeswoman declined to comment.

In his tests, Nohl said he was able to gain remote access to a computer by having the USB instruct the computer to download a malicious program with instructions that the PC believed were coming from a keyboard.

He was also able to change DNS network settings and instruct the machine to route internet traffic through malicious servers.

Once a computer is infected, it could be programmed to infect all USB devices that are subsequently attached to it, which would then corrupt machines that they contact.

"Now all of your USB devices are infected. It becomes self-propagating and extremely persistent," Nohl said. "You can never remove it."

Christof Paar, a professor of electrical engineering at Germany's University of Bochum who reviewed the findings, said he believed the new research would prompt others to take a closer look at USB technology, and potentially lead to the discovery of more bugs.

He urged manufacturers to improve protection of their chips to thwart attacks.

"The manufacturer should make it much harder to change the software that runs on a USB stick," Paar said.