Efficient Privilege De-Escalation for Ad Libraries in Mobile Apps

The proliferation of mobile apps is due in part to the advertising ecosystem which enables developers to earn revenue while providing free apps. Ad-supported apps can be developed rapidly with the availability of ad libraries. However, today?s ad libraries essentially have access to the same resources as the parent app, and this has caused signi?cant privacy concerns. In this paper, we explore ef?cient methods to de-escalate privileges for ad libraries where the resource access privileges for ad libraries can be different from that of the app logic. Our system, PEDAL, contains a novel machine classi?er for detecting ad libraries even in the presence of obfuscated code, and techniques for automatically instrumenting bytecode to effect privilege de-escalation even in the presence of privilege inheritance. We evaluate PEDAL on a large set of apps from the Google Play store and demonstrate that it has a 98% accuracy in detecting ad libraries and imposes less than 1% runtime overhead on apps.