Jekyll on iOS: when benign apps become evil

Abstract

Apple adopts the mandatory app review and code sign-ing mechanisms to ensure that only approved apps can run on iOS devices. In this paper, we present a novel attack method that fundamentally defeats both mecha-nisms. Our method allows attackers to reliably hide ma-licious behavior that would otherwise get their app re-jected by the Apple review process. Once the app passes the review and is installed on an end user’s device, it can be instructed to carry out the intended attacks. The key idea is to make the apps remotely exploitable and subsequently introduce malicious control flows by rearranging signed code. Since the new control flows do not exist during the app review process, such apps, namely Jekyll apps, can stay undetected when reviewed and easily obtain Apple’s approval. We implemented a proof-of-concept Jekyll app and successfully published it in App Store. We remotely launched the attacks on a controlled group of devices that installed the app. The result shows that, despite run-ning inside the iOS sandbox, Jekyll app can successfully perform many malicious tasks, such as stealthily posting tweets, taking photos, stealing device identity informa-tion, sending email and SMS, attacking other apps, and even exploiting kernel vulnerabilities. 1