DEF CON 25 - Mark Williams, Rob Stanley - If You Give a Mouse a Microchip
Channel: DEFCONConference
Date: 2017-11-02

The International, a recent esports tournament, had a 20 million dollar prize pool with over five million people tuned in to the final match. The high stakes environment at tournaments creates an incentive for players to cheat for a competitive advantage. Cheaters are always finding new ways to modify software, from attempting to sneak executables in on flash drives, to using cheats stored in Steam's online workshop which bypasses IP restrictions.

This presentation describes how one can circumvent existing security controls to sneak a payload (game cheat) onto a target computer. Esports tournaments typically allow players to provide their own mouse and keyboard, as these players prefer to use specific devices or may be obligated to use a sponsor branded device. These "simple" USB input devices can still be used to execute complex commands on a computer via the USB Human Interface Device (HID) protocol.

Our attack vector is a mouse with an ARM Cortex M series processor. The microcontroller stores custom user profiles in flash memory, allowing the mouse to retain user settings between multiple computers. We modify the device's firmware to execute a payload delivery program, stored in free space in flash memory, before returning the mouse to its original functionality. Retaining original functionality allows the mouse to be used discreetly, as it is an "expected" device at these tournaments. This concept applies to any USB device that uses this processor, and does not require obvious physical modifications. 

This delivery method has tradeoffs. Our exploit is observable, as windows are created and in focus during payload delivery. The advantage to this approach is that it bypasses other security measures that are commonly in place, such as filtered internet traffic and disabled USB mass storage.