CVE-2016-2384: arbitrary code execution due to a bug in usb-midi linux driver

Video demo right here https://www.youtube.com/watch?v=lfl1NJn1nvo

Fortunately it cannot connect malicious USB dongles. Yet.

This is an excellent writeup, IMO. It's a clear demonstration of how use after free can be so dangerous.

Short version: A bug in a Linux USB device driver can be caused to take over a Linux machine by plugging in a malicious USB device. An attacker would either use a custom USB dongle, or a programmable device with a USB connection such as a cell phone.

There's a narrow problem here, which is the bug in the device driver. That'll be fixed of course, now that it's gotten attention. But fixing this bug will not solve the problem, because there is a truly enormous number of different USB device drivers, most of which are poorly audited, run in kernel space, and correspond to unusual hardware. The real problem is that plugging in a device can cause any obscure device driver to load, without user confirmation. So for example, someone can plug in a cell phone, and the cell phone can claim to be an obscure kind of printer that no one has seen since the 90s, and the system will go ahead and load that device driver.

The solution is to require user confirmation before accepting any USB device that hasn't been seen before. Just a simple popup: You have connected [type of device], Ok/Cancel. The only tricky part is input devices like keyboards and mice, where this could create a chicken-and-egg problem with the confirmation prompt. (And devices pretending to be keyboards can be dangerous; they can type commands). Fortunately, there is a solution, albeit one which will take some programming work: accept keyboard input from keyboards that have either been confirmed by a prompt or have typed the user's login password. (Since some "keyboards" are actually things like barcode scanners).

Another solution is to not compile drivers that you don't need, and to take minimizing kernel attack space as seriously as running a firewall. It should, in my opinion, be routine to run a reduced kernel in production, however most of the industry appears to use stock kernels from a few major vendors. The likes of CoreOS are probably helping here. Keep it up.