The success of Android phones makes them a prominent target for malicious software, in particular since the Android permission system turned out to be inadequate to protect the user against security and privacy threats. This work presents AppGuard, a powerful and flexible system for the enforcement of user-customizable security policies on untrusted Android applications. AppGuard does not require any changes to a smartphone's firmware or root access. Our system offers complete mediation of security-relevant methods based on callee-site inline reference monitoring. We demonstrate the general applicability of AppGuard by several case studies, e.g., removing permissions from overly curious apps as well as defending against several recent real-world attacks on Android phones. Our technique exhibits very little space and runtime overhead. AppGuard is publicly available, has been invited to the Samsung Apps market, and has had more than 500,000 downloads so far.

Android's success makes it a prominent target for malicious software. However, the user has very limited control over security-relevant operations. This work presents AppGuard, a powerful and flexible security system that overcomes these deficiencies. It enforces user-defined security policies on untrusted Android applications without requiring any changes to a smartphone's firmware, root access, or the like. Finegrained and stateful security policies are expressed in a formal specification language, which also supports secrecy requirements. Our system offers complete mediation of security-relevant methods based on calleesite inline reference monitoring and supports widespread deployment. In the experimental analysis we demonstrate the removal of permissions for overly curious apps as well as how to defend against several recent real-world attacks on Android phones. Our technique exhibits very little space and runtime overhead. The utility of AppGuard has already been demonstrated by more than 1,000,000 downloads.

Google's Android OS provides a lightweight IPC mechanism called Binder, which enables the development of feature-rich apps that seamlessly integrate services and data of other apps. Whenever apps can act both as service consumers and service providers, it is inevitable that the IPC mechanism provides message receivers with message provenance information to establish trust. However, the Android OS currently fails in providing sufficient provenance information, which has led to a number of attacks.We present an extension to the Android IPC mechanism, called Scippa, that establishes IPC call-chains across application processes. Scippa provides provenance information required to effectively prevent recent attacks such as confused deputy attacks. Our solution constitutes a system-centric approach that extends the Binder kernel module and Android's message handlers. Scippa integrates seamlessly into the system architecture and our evaluation shows a performance overhead of only 2.23% on Android OS v4.2.2.