“Back in July 2013, The Washington Post reported that nearly a decade ago, the National Security Agency developed a new technique that allowed spooks to “find cellphones even when they were turned off. JSOC troops called this ‘The Find,’ and it gave them thousands of new targets, including members of a burgeoning al-Qaeda-sponsored insurgency in Iraq, according to members of the unit.”
“Many security researchers scratched their heads trying to figure out how this could be so.
security/2013/11/samsung- nokia-say-they-dont-know-how- to-track-a-powered-down-phone/
“Every smartphone or other device with mobile communications capability (e.g. 3G or LTE) actually runs not one, but two operating systems. Aside from the operating system that we as end-users see (Android, iOS, PalmOS), it also runs a small operating system that manages everything related to radio. Since this functionality is highly timing-dependent, a real-time operating system is required.
“This operating system is stored in firmware, and runs on the baseband processor. This baseband RTOS is always entirely proprietary. For instance, the RTOS inside Qualcomm baseband processors (in this specific case, the MSM6280) is called AMSS, built upon their own proprietary REX kernel, and is made up of 69 concurrent tasks, handling everything from USB to GPS. It runs on an ARMv5 processor.
The problem here is clear: these baseband processors and the proprietary, closed software they run are poorly understood, as there’s no proper peer review. This is actually kind of weird, considering just how important these little bits of software are to the functioning of a modern communication device. You may think these baseband RTOS’ are safe and secure, but that’s not exactly the case. You may have the most secure mobile operating system in the world, but you’re still running a second operating system that is poorly understood, poorly documented, proprietary, and all you have to go on are Qualcomm’s Infineon’s, and others’ blue eyes.
The insecurity of baseband software is not by error; it’s by design. The standards that govern how these baseband processors and radios work were designed in the ’80s, ending up with a complicated codebase written in the ’90s – complete with a ’90s attitude towards security. For instance, there is barely any exploit mitigation, so exploits are free to run amok. What makes it even worse, is that every baseband processor inherently trusts whatever data it receives from a base station (e.g. in a cell tower). Nothing is checked, everything is automatically trusted.
Lastly, the baseband processor is usually the master processor, whereas the application processor (which runs the mobile operating system) is the slave.
So, we have a complete operating system, running on an ARM processor, without any exploit mitigation (or only very little of it), which automatically trusts every instruction, piece of code, or data it receives from the base station you’re connected to. What could possibly go wrong?
The Tap Blog is a collective of like-minded researchers and writers who’ve joined forces to distribute information and voice opinions avoided by the world’s media.