SDLI: Static Detection of Leaks Across Intents

Intents are Android's intra and inter-application communication mechanism. They specify an action to perform, with extra data, and are sent to a receiver component or broadcast to many components. Components, in the same or in a distinct app, receive the intent if they are available to perform the desired action. Hence, a sound static analyzer must be aware of information flows through intents. That can be achieved by considering intents as both source (when reading) and sink (when writing) of confidential data. But this is overly conservative if the intent stays inside the same app or if the set of apps installed on the device is known in advance. In such cases, a sound approximation of the flow of intents leads to a more precise analysis. This work describes SDLI, a novel static analyzer that, for each app, creates an XML summary file reporting a description of the tainted information in outwards intents and of the intents the app is available to serve. SDLI discovers confidential information leaks when two apps communicate, by matching their XML summaries, looking for tainted outwards intents of the first app that can be inwards intents of the second app. The tool is implemented inside Julia, an industrial static analyzer. On the DroidBench testcases, its shows a precision higher than 75%. On some popular apps from the Google Play marketplace, it spots inter-apps leaks of confidential data, hence showing its practical effectiveness.