SafetyNOT

Many apps performing security-sensitive tasks (e.g., online banking) attempt to verify the integrity of the device they are running in and the integrity of their own code. To ease this goal, Android provides an API, called the SafetyNet Attestation API, that can be used to detect if the device an app is running in is in a "safe" state (e.g., non-rooted) and if the app's code has not been modified (using, for instance, app repackaging). In this paper, we perform the first large-scale systematic analysis of the usage of the SafetyNet API. Our study identifies many common mistakes that app developers make when attempting to use this API. Specifically, we provide a systematic categorization of the possible misusages of this API, and we analyze how frequent each misuse is. Our results show that, for instance, more than half of the analyzed apps check SafetyNet results locally (as opposed to using a remote trusted server), rendering their checks trivially bypassable. Even more surprisingly, we found that none of the analyzed apps invoking the SafetyNet API uses it in a fully correct way.