Inside Job: Understanding and Mitigating the Threat of External Device Mis-Bonding on Android

Today’s smartphones can be armed with many types of external devices, such as medical devices and credit card readers, that enrich their functionality and enable them to be used in application domains such as healthcare and retail. This new development comes with new security and privacy challenges. Existing phone-based operating systems, Android in particular, are not ready for protecting authorized use of these external devices: indeed, any app on an Android phone that acquires permission to utilize communication channels like Bluetooth and Near Field Communications is automatically given the access to devices communicating with the phone on these channels. In this paper, we present the first study on this new security issue, which we call external Device Mis-Bonding or DMB, under the context of Bluetooth-enabled Android devices. Our research shows that this problem is both realistic and serious: oftentimes an unauthorized app can download sensitive user data from an Android device and also help the adversary to deploy a spoofed device that injects fake data into the original device’s official app on the phone. Specifically, we performed an in-depth analysis on four popular health/medical devices that collect sensitive user information and successfully built end-to-end attacks that stealthily gathered sensitive user data and fed arbitrary information into the user’s health/medical account, using nothing but Bluetooth permissions and public information disclosed by the phone. Our further study of 68 relevant device-using apps from Google Play confirms that the vast majority of the devices on the market are vulnerable to this new threat. To defend against it, we developed the first OS-level protection, called Dabinder. Our approach automatically generates secure bonding policies between a device and its official app, and enforces them when an app attempts to establish Bluetooth connections with a device and unpair the phone from the device (for resetting the Bluetooth link key). Our evaluation shows that this new technique effectively thwarts the DMB attacks and incurs only a negligible impact on the phone’s normal operations.