Analyzing Unsafe and Malicious Dynamic Code Loading in Android Applications

The design of the Android system allows applications to load additional code from external sources at runtime. On the one hand, malware can use this capability to add malicious functionality after it has been inspected by an application store or anti-virus engine at installation time. On the other hand, developers of benign applications can inadvertently introduce vulnerabilities. In this paper, we systematically analyze the security implications of the ability to load additional code in Android. We developed a static analysis tool to automatically detect attempts to load external code using static analysis techniques, and we performed a large-scale study of 1,632 popular applications from the Google Play store, showing that loading external code in an insecure way is a problem in as much as 9.25% of those applications and even 16% of the top 50 free applications. We also show how malware can use code-loading techniques to avoid detection by exploiting a conceptual weakness in current Android malware protection. Finally, we propose modifications to the Android framework that enforce integrity checks on code to mitigate the threats imposed by the ability to load external code.