Third-party libraries are commonly used by app developers for alleviating the development efforts and for monetizing their apps. On Android, the host app and its third-party libraries reside in the same sandbox and share all privileges awarded to the host app by the user, putting the users' privacy at risk of intrusions by third-party libraries. In this paper, we introduce a new privilege separation approach for third-party libraries on stock Android. Our solution partitions Android applications at compile-time into isolated, privilege-separated compartments for the host app and the included third-party libraries. A particular benefit of our approach is that it leverages compiler-based instrumentation available on stock Android versions and thus abstains from modification of the SDK, the app bytecode, or the device firmware. A particular challenge for separating libraries from their host apps is the reconstruction of the communication channels and the preservation of visual fidelity between the now separated app and its libraries. We solve this challenge through new IPC-based protocols to synchronize layout and lifecycle management between different sandboxes. Finally, we demonstrate the efficiency and effectiveness of our solution by applying it to real world apps from the Google Play Store that contain advertisements.

With the introduction of Android 5 Lollipop, the Android Runtime (ART) superseded the Dalvik Virtual Machine (DVM) by introducing ahead-of-time compilation and native execution of applications, effectively deprecating seminal works such as TaintDroid that hitherto depend on the DVM. In this paper, we discuss alternatives to overcome those restrictions and highlight advantages for the security community that can be derived from ART's novel on-device compiler dex2oat and its accompanying runtime components. To this end, we introduce ARTist, a compiler-based application instrumentation solution for Android that does not depend on operating system modifications and solely operates on the application layer. Since dex2oat is yet uncharted, our approach required first and foremost a thorough study of the compiler suite's internals and in particular of the new default compiler backend called Optimizing. We document the results of this study in this paper to facilitate independent research on this topic and exemplify the viability of ARTist by realizing two use cases. In particular, we conduct a case study on whether taint tracking can be re-instantiated using a compiler-based app instrumentation framework. Overall, our results provide compelling arguments for the community to choose compiler-based approaches over alternative bytecode or binary rewriting approaches for security solutions on Android.

On Android, advertising libraries are commonly integrated with their host apps. Since the host and advertising components share the application's sandbox, advertisement code inherits all permissions and can access host resources with no further approval needed. Motivated by the privacy risks of advertisement libraries as already shown in the literature, this poster introduces an Android Runtime (ART) based app compartmentalization mechanism to achieve separation between trusted app code and untrusted library code without system modification and application rewriting. With our approach, advertising libraries will be isolated from the host app and the original app will be partitioned into two sub-apps that run independently, with the host app's resources and permissions being protected by Android's app sandboxing mechanism. ARTist [1], a compiler-based Android app instrumentation framework, is utilized here to recreate the communication channels between host and advertisement library. The result is a robust toolchain on device which provides a clean separation of developer-written app code and third-party advertisement code, allowing for finer-grained access control policies and information flow control without OS customization and application rebuilding.

Dynamic analysis and taint tracking on Android was typically implemented by instrumenting the Dalvik Virtual Machine. However, the new Android Runtime (ART) introduced in Android 5 replaces the interpreter with an on-device compiler suite. Therefore as of Android 5, the applicability of interpreter instrumentation-based approaches like TaintDroid is limited to Android versions up to 4.4 Kitkat. In this poster, we present ongoing work on re-enabling taint tracking for apps by instrumenting the Optimizing backend, used by the new ART compiler suite for code generation. As Android now compiles apps ahead-of-time from dex bytecode to platform specific native code on the device itself, an instrumented compiler provides the opportunity to emit additional instructions that enable the actual taint tracking. The result is a custom compiler that takes arbitrary app APKs and transforms them into self-taint tracking native code, executable by the Android Runtime.