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It has been demonstrated in numerous previous studies that Android and its underlying Linux operating systems do not properly isolate mobile apps to prevent cross-app side- channel attacks. Cross-app information leakage enables malicious Android apps to infer sensitive user data (e.g., passwords), or private user information (e.g., identity or location) without requiring specific permissions. Nevertheless, no prior work has ever studied these side-channel attacks on iOS-based mobile devices. One reason is that iOS does not implement procfs— the most popular side-channel attack vector; hence the previously known attacks are not feasible. In this paper, we present the first study of OS-level side-channel attacks on iOS. Specifically, we identified several new side-channel attack vectors (i.e., iOS APIs that enable cross-app information leakage); developed machine learning frameworks (i.e., classification and pattern matching) that combine multiple attack vectors to improve the accuracy of the inference attacks; demonstrated three categories of attacks that exploit these vectors and frameworks to exfiltrate sensitive user information. We have reported our findings to Apple and proposed mitigations to the attacks. Apple has incorporated some of our suggested countermeasures into iOS 11 and MacOS High Sierra 10.13 and later versions.
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The Danger of Minimum Exposures: Understanding Cross-App Information Leaks on iOS through Multi-Side-Channel Learning
Research on side-channel leaks has long been focusing on the information exposure from a single channel (memory, network traffic, power, etc.). Less studied is the risk of learning from multiple side channels related to a target activity (e.g., website visits) even when individual channels are not informative enough for an effective attack. Although the prior research made the first step on this direction, inferring the operations of foreground apps on iOS from a set of global statistics, still less clear are how to determine the maximum information leaks from all target-related side channels on a system, what can be learnt about the target from such leaks and most importantly, how to control information leaks from the whole system, not just from an individual channel. To answer these fundamental questions, we performed the first systematic study on multi-channel inference, focusing on iOS as the first step. Our research is based upon a novel attack technique, called Mischief, which given a set of potential side channels related to a target activity (e.g., foreground apps), utilizes probabilistic search to approximate an optimal subset of the channels exposing most information, as measured by Merit Score, a metric for correlation-based feature selection. On such an optimal subset, an inference attack is modeled as a multivariate time series classification problem, so the state-of-the-art deep-learning based solution, InceptionTime in particular, can be applied to achieve the best possible outcome. Mischief is found to work effectively on today's iOS (16.2), identifying foreground apps, website visits, sensitive IoT operations (e.g., opening the door) with a high confidence, even in an open-world scenario, which demonstrates that the protection Apple puts in place against the known attack is inadequate. Also importantly, this new understanding enables us to develop more comprehensive protection, which could elevate today's side-channel research from suppressing leaks from individual channels to controlling information exposure across the whole system.
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- Award ID(s):
- 2207231
- PAR ID:
- 10531853
- Publisher / Repository:
- ACM
- Date Published:
- ISBN:
- 9798400700507
- Page Range / eLocation ID:
- 281 to 295
- Format(s):
- Medium: X
- Location:
- Copenhagen Denmark
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Conference Paper:
- https://doi.org/10.1145/3576915.3616655
