Leaking the Privacy of Groups and More: Understanding Privacy Risks of Cross-App Content Sharing in Mobile Ecosystem

— Cross-app content sharing is one of the prominent features widely used in mobile apps. For example, a short video from one app can be shared to another (e.g., a messaging app) and further viewed by other users. In many cases, such Cross-app content sharing activities could have privacy implications for both the sharer and sharee, such as exposing app users’ personal interests. In this paper, we provide the first in-depth study on the privacy implications of Cross-app content sharing (as we call Cracs ) activities in the mobile ecosystem. Our research showed that during the sharing process, the adversary can not only track and infer user interests as traditional web trackers but also cause other severe privacy implications to app users. More specifically, due to multiple privacy-intrusive designs and implementations of Cracs , an adversary can easily reveal a user’s social relations to an outside party, or unnecessarily expose user identities and her associated personal data (e.g., user accounts in another app). Such privacy implications are indeed a concern for app users, as confirmed by a user study we have performed with 300 participants. To further evaluate the impact of our identified privacy implications at large, we have designed an automatic pipeline named Shark , combined with static analysis and dynamic analysis to effectively identify whether a given app introduces unnecessary data exposure in Cracs . We analyzed 300 top downloaded apps collected from app stores in both the US and China. The analysis results showed