Collect Responsibly But Deliver Arbitrarily?: A Study on Cross-User Privacy Leakage in Mobile Apps

Recent years have witnessed the interesting trend that modern mobile apps perform more and more likely as user-to-user platforms, where app users can be freely and conveniently connected. Upon these platforms, rich and diverse data is often delivered across users, which brings users great conveniences and plentiful services, but also introduces privacy security concerns. While prior work has primarily studied illegitimate personal data collection problems in mobile apps, few paid little attention to the security of this emerging user-to-user platform feature, thus providing a rather limited understanding of the privacy risks in this aspect.