When Web Meets Mobile: Novel Security Threats and Defenses in Web/Mobile Hybrid Apps

Nowadays, mobile app developers are enjoying the benefits of the amalgamation of web and mobile platforms. Developers can easily and smoothly integrate all sorts of web services in their mobile apps by embedding a browser-like UI component, called “WebView”, which can render web content and run JavaScript code within mobile apps (call hybrid apps for convenience). WebView is easy to use and popular. A recent study showed ~80% of Android apps used WebView. WebView is also as powerful as regular browsers (e.g., Chrome/Chromium), and well supports web features and behaviors. In regular browsers, there exist several sensitive web behaviors that are often the root reason of critical security issues. In past years, they have been well studied, and a variety of mature defense solutions have been deployed. However, these sensitive web behaviors are seldom understood and scrutinized in WebView, which provides a totally new working environment. Different from regular browsers, WebView offers mobile developers freedom to customize their WebView instances by enabling several unique programming features. For example, WebView allows mobile code to control and customize web behaviors through WebView setting and event handler APIs. Considering these WebView features may heavily impact above sensitive web behaviors, it is unclear whether the corresponding defense solutions are still effective in WebView. Motivated by above security concerns, in this dissertation, we conduct the systematic security study of several sensitive web behaviors (e.g., web events, web messaging, and the utilization of iframes and popups) in WebView of the Android platform, which is open and the biggest mobile operating system (OS). As a consequence, we discover several novel security vulnerabilities and fundamental design flaws. To demonstrate the security implications, we devise several concrete attacks. Through these attacks, untrusted code (e.g., ads) loaded in WebView can open holes on existing defense solutions, and obtain risky privileges and abilities, such as stealing users’ private data (e.g., GPS location), unauthorizedly accessing sensitive hardware (e.g., microphone), and performing phishing attacks. Then, we study and assess the security impacts of these security issues on real-world hybrid apps. For this purpose, we develop novel tools that can automatically apply program analysis techniques to vet Android apps. By analyzing a large number of most popular apps collected from the official Android marketplace, we find the vulnerabilities are prevalent. Many high-profile apps are verified to be impacted, such as Facebook, Instagram, Facebook Messenger, Google News, Skype, Uber, Yelp, and U.S. Bank. To mitigate these security issues from the root, we design multi-level defense solutions that enhance the security of WebView. Our evaluation on real-world apps shows our mitigation solutions are effective and scalable, with negligible overhead