Pierluigi Paganini November 13, 2014

The researcher Karsten Nohl and his team presented an update on their BadUSB study.It is impossible to discriminate patchable devices from unpatchable ones.

Earlier August 2014 the security expert Karsten Nohl and his team discovered that an attacker could exploit a new class of attacks based on a USB device to compromise a targeted machine. The attack could be used to compromise personal computers and is able to evade all actual security protections loading malicious software in low-cost computer chips that control the functions of USB devices.

“Nohl and Lell’s BadUSB demonstrations during Black Hat illustrated how their code could overwrite USB firmware and turn a USB device into anything. A flash drive plugged into a PC, could for example, emulate a keyboard and issue commands that steal data from the machine, spoof a computer’s network interface and redirect traffic by altering DNS settings, or could load malware from a hidden partition on the drive.”

The researchers point a series of flaws in the software used to run tiny electronic components, these components are usually designed without protections against tampering with their code. Hackers can uncover such flaws and exploit them creating serious problems to the targeted architecture.

“You cannot tell where the virus came from. It is almost like a magic trick,” said Nohl.

As reported in a blog post published by Wired unpatchable security flaw in USB devices affects only the fifty percent of USB devices, but it is nearly impossible to discriminate secure USB units from the insecure ones “without ripping open every last thumb drive”.

Last week Nohl, and his fellow researchers Jakob Lell and Sascha Krissler, presented an update to his BadUSB research at the PacSec security conference in Tokyo. The experts analyzed the USB controller chips sold by the eight biggest vendors (Phison, Alcor, Renesas, ASmedia, Genesys Logic, FTDI, Cypress and Microchip) discovering that half of them were vulnerable to the attack, but the expert revealed that it was impossible to predict which chip a device uses is impossible for the final user.

“It’s not like you plug [a thumbdrive] into your computer and it tells you this is a Cypress chip, and this one is a Phison chip,” says Nohl, naming two of the top USB chip manufacturers. “You really can’t check other than by opening the device and doing the analysis yourself…The scarier story is that we can’t give you a list of safe devices.”

The experts analyzed versions of each chip both by looking up its published specs and by plugging a device using it into a USB port and attempting to overwrite the firmware in the chip.

“They found an unpredictable patchwork of results. All of the USB storage controllers from Taiwanese firm Phison that Nohl tested, for instance, were vulnerable to reprogramming. Chips from ASmedia weren’t, Nohl’s tests found. Controller chips from fellow Taiwanese company Genesys that used the USB 2 standard were immune, but ones that used the newer USB 3 standard were susceptible. In other categories of device like USB hubs, keyboards, webcams and mice, the results produced an even messier Excel spreadsheet of “vulnerable,” “secure,” and “inconclusive.”” reports Wired.

Unfortunately, device makers don’t provide info on the manufacture of the chips they have integrated, in some cases, they use chips from different vendors, even in the same product, this politic allows them to choose the cheapest suppliers for different lots of production.

The only way to prevent the exploitation of the BadUSB is to request device makers to label the chips they use in their products.

“You’d never get away with this in a laptop. People would go crazy if they bought a computer and it wasn’t the chip they saw in the review they read,” explains Nohl. “It’s just these USB devices that come as black boxes.”

It’s clear that what Nohl suggest is quite impossible to realize, so the researcher decided not to release the proof-of-concept code for his BadUSB attack when he demonstrated it at Black Hat.

The company Imation already implemented a solution to protect its users against the BadUSB attacks, its solution Ironkey requires that any new updates to its chip firmware be digitally signed with an unforgeable cryptographic signature. The process was designed to prevent malicious reprogramming of the USB firmware. According to Nohl, other USB makers could adopt the same strategy to secure their users.

Nohl highlighted that the total lack of transparency in the USB device industry exposes everyone uses a USB device to the risk of attack, every device is potentially exploitable by bad actors.

“Some people have accepted that USB is insecure. Others remember BadUSB only as the Phison bug. That second group needs to wake up to the same level of awareness of the first group,” Nohl says. “For practical purposes, it affects potentially everything.”

Pierluigi Paganini

(Security Affairs –  BadUSB, hacking)

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