Mobile Security 1

06 April 2017, 09:30, A6-004

Session chair: N. Asokan Aalto University, Finland

SPOKE: Scalable Knowledge Collection and Attack Surface Analysis of Access Control Policy for Security Enhanced Android

Ruowen Wang, Ahmed M. Azab, William Enck, Ninghui Li, Peng Ning, Xun Chen, Wenbo Shen, Yueqiang Cheng

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SEAndroid is a mandatory access control (MAC) framework that can confine faulty applications on Android. Nevertheless, the effectiveness of SEAndroid enforcement depends on the employed policy. The growing complexity of Android makes it difficult for policy engineers to have complete domain knowledge on every system functionality. As a result, policy engineers sometimes craft over-permissive and ineffective policy rules, which unfortunately increased the attack surface of the Android system and have allowed multiple real-world privilege escalation attacks. We propose SPOKE, an SEAndroid Policy Knowledge Engine, that systematically extracts domain knowledge from rich-semantic functional tests and further uses the knowledge for characterizing the attack surface of SEAndroid policy rules. Our attack surface analysis is achieved by two steps: 1) It reveals policy rules that cannot be justified by the collected domain knowledge. 2) It identifies potentially over-permissive access patterns allowed by those unjustified rules as the attack surface. We evaluate SPOKE using 665 functional tests targeting 28 different categories of functionalities developed by Samsung Android Team. SPOKE successfully collected 12,491 access patterns for the 28 categories as domain knowledge, and used the knowledge to reveal 320 unjustified policy rules and 210 over-permissive access patterns defined by those rules, including one related to the notorious libstagefright vulnerability. These findings have been confirmed by policy engineers.

Android Database Attacks Revisited

Behnaz Hassanshahi, Roland H. C. Yap

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Many Android apps (applications) employ databases for managing sensitive data, thus, security of their databases is a concern. In this paper, we systematically study attacks targeting databases in benign Android apps. In addition to studying database vulnerabilities accessed from content providers, we define and study a new class of database vulnerabilities. We propose an analysis framework to find such vulnerabilities with a proof-of-concept exploit. Our analysis combines static dataflow analysis, symbolic execution with models for handling complex objects such as URIs and dynamic testing. We evaluate our analysis on popular Android apps, successfully finding many database vulnerabilities. Surprisingly, our analyzer finds new ways to exploit previously reported and fixed vulnerabilities. Finally, we propose a fine-grained protection mechanism extending the manifest to protect against database attacks.

TriFlow: Triaging Android Applications using Speculative Information Flows

Omid Mirzaei, Guillermo Suarez-Tangil, Juan Tapiador, Jose M. de Fuentes, Guillermo Suarez-Tangil

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Information flows in Android can be effectively used to give an informative summary of an application’s behavior, showing how and for what purpose apps use specific pieces of information. This has been shown to be extremely useful to characterize risky behaviors and, ultimately, to identify unwanted or malicious applications in Android. However, identifying information flows in an application is computationally highly expensive and, with more than one million apps in the Google Play market, it is critical to prioritize applications that are likely to pose a risk. In this work, we develop a triage mechanism to rank applications considering their potential risk. Our approach, called TriFlow, relies on static features that are quick to obtain. TriFlow combines a probabilistic model to predict the existence of information flows with a metric of how significant a flow is in benign and malicious apps. Based on this, TriFlow provides a score for each application that can be used to prioritize analysis. TriFlow also provides an explanatory report of the associated risk. We evaluate our tool with a representative dataset of benign and malicious Android apps. Our results show that it can predict the presence of information flows very accurately and that the overall triage mechanism enables significant resource saving.