Stuck in the Permissions With You:Developer & User Perspectives on App Permissions & Their Privacy Ramifications

While the literature on permissions from the end-user perspective is rich, there is a lack of empirical research on why developers request permissions, their conceptualization of permissions, and how their perspectives compare with end-users’ perspectives. Our study aims to address these gaps using a mixed-methods approach.Through interviews with 19 app developers and a survey of 309 Android and iOS end-users, we found that both groups shared similar concerns about unnecessary permissions breaking trust, damaging the app’s reputation, and potentially allowing access to sensitive data. We also found that developer participants sometimes requested multiple permissions due to confusion about the scope of certain permissions or third-party library requirements. Additionally, most end-user participants believed they were responsible for granting a permission request, and it was their choice to do so, a belief shared by many developer participants. Our findings have implications for improving the permission ecosystem for both developers and end-users

INTERACTION-BASED SECURITY FOR MOBILE APPS

Mobile operating systems pervade our modern lives. Security and privacy is of particular concern on these systems, as they have access to a wide range of sensitive resources. Apps access these sensitive resources to help users perform tasks. However, apps may use these sensitive resources in a way that the user does not expect. For example, an app may look up reviews of restaurants nearby, but also leak the user’s location to an ad service every hour. I claim that interaction serves as a valuable component of security decisions, because the user’s interaction with the app’s user interface (UI) deeply informs their mental model of how apps access sensitive data. I introduce the notion of interaction-based security, wherein security decisions are driven by this interaction. To help understand and enforce interaction-based security, I present four pieces of work. The first is Redexer, which performs binary instrumentation of off-the-shelf Android binaries. Binary instrumentation is a useful tool for enforcing and studying security properties. I demonstrate one example of how Redexer can be used to study location privacy in apps. Android permissions constrain how data enters apps, but do not constrain how the information is used or where it goes. Information-flow allows us to formally define what it means for data to leak from applications, but it is unclear how to use information-flow policies for Android apps, because apps frequently declassify information. I define interaction-based declassification policies, and show how they can be used to define policies for several example apps. I then implement a symbolic executor which checks Android apps to ensure they respect these policies. Next, I test the hypothesis that the app’s UI influences security decisions. I outline an app study that measures when apps use sensitive resources with respect to their UI. I then conduct a user study to measure how an app’s UI influences their expectation that a sensitive resource will be accessed. I find that interactivity plays a large role in determining user expectation of sensitive resource use, and that apps largely access sensitive resources interactively. I also find that users may not always understand background uses of these sensitive resources and using them expectation requires special care in some circumstances. Last, I present a tool which can help a security auditor quickly understand how apps use resources. My tool uses a novel combination of app logging, symbolic execution, and abstract interpretation to infer a formula that holds on each per- mission use. I evaluate my tool on several moderately-sized apps and show that it infers the same formulas we laboriously found by hand

On Understanding Permission Usage Contextuality of Android Apps

In the runtime permission model, the context in which a permission is requested/used the first time may change later without the user's knowledge. Prior research identifies user dissatisfaction on varying contexts of permission use in the install-time permission model. However, the contextual use of permissions by the apps that are developed/adapted for the runtime permission model has not been studied. Our goal is to understand how permissions are requested and used in different contexts in the runtime permission model, and compare them to identify potential abuse. We present ContextDroid, a static analysis tool to identify the contexts of permission request and use. Using this tool, we analyze 38,838 apps (from a set of 62,340 apps) from the Google Play Store. We devise a mechanism following the best practices and permission policy enforcement by Google to flag apps for using permissions in potentially unexpected contexts. We flag 30.20\% of the 38,838 apps for using permissions in multiple and dissimilar contexts. Comparison with VirusTotal shows that non-contextual use of permissions can be linked to unwanted/malicious behaviour: 34.72\% of the 11,728 flagged apps are also detected by VirusTotal (i.e., 64.70\% of the 6,295 VirusTotal detected apps in our dataset). We find that most apps don't show any rationale if the user previously denied a permission. Furthermore, 13\% (from the 22,567 apps with identified request contexts) apps show behaviour similar to the install-time permission model by requesting all dangerous permissions when the app is first launched. We hope this thesis will bring attention to non-contextual permission usage in the runtime model, and may spur research into finer-grained permission control