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Femtocells wilt under attack

Tiny, tiny, tiny root box danger

Security researchers have turned their attention to femtocells, and have discovered that gaining root on the tiny mobile base stations isn't as hard as one might hope.

Researchers working for TrustWave will present details of their successful attacks against femtocells at the ShmooCon security conference next week in Washington. They will explain that they were able to gain root access to the Linux-based devices, which could then be tampered with to track users and intercept calls.

"Cell phones are programmed to trust the cell tower. The cell phone does not possess business logic to avoid connecting to a wireless device, acting as a tower, which has experienced tampering," the company points out in its release about the work. That's true, though given that almost all femtocells are 3G devices, and the 3G standard includes network (as well as handset) authentication, the risk is more about interception of communication rather than compromising the security of the network itself.

And even that interception will be of limited value if both network and handset are using the more-advanced A5/3 encryption algorithm (as specified in the 3G standard). So unless our attacker can exploit the theoretical cracks in A5/3, our compromised femtocell is pretty much reduced to "monitor[ing] the movement of people based on their unique cell phone identification number." Even TrustWave admits that "while this is not a security implication, it is a loss of privacy."

The researchers told eWeek that after "hours of sniffing traffic, changing IP address ranges, guessing passwords and investigating hardware pinouts," they "obtained root access on these Linux-based cellular-based devices". The specifics won't be revealed until the presentation next week, but will be very dependent on the femtocell's manufacturer, as the equipment is far from standard at this point.

Man-in-the-middle attacks have been possible on mobile networks for some years, and femtocell technology makes such an attack easier and cheaper to mount. It's possible to imagine a spy planting a fake base station in the office of a rival-corporation's CEO to intercept communications, though the sudden availability of a high-strength 3G signal might give things away. ®

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