Cryptographic functions play a critical role in the secure transmission and storage of application data. Although most crypto functions are well-defined and carefully-implemented in standard libraries, in practice, they could be easily misused or incorrectly encapsulated due to its error-prone nature and inexperience of developers. This situation is even worse in the IoT domain, given that developers tend to sacrifice security for performance in order to suit resource-constrained IoT devices. Given the severity and the pervasiveness of such bad practice, it is crucial to raise public awareness about this issue, find the misuses and shed light on best practices. In this paper, we design and implement CRYPTOREX, a framework to identify crypto misuse of IoT devices under diverse architectures and in a scalable manner. In particular, CRYPTOREX lifts binary code to a unified IR and performs static taint analysis across multiple executables. To aggressively capture and identify misuses of self-defined crypto APIs, CRYPTOREX dynamically updates the API list during taint analysis and automatically tracks the function arguments. Running on 521 firmware images with 165 pre-defined crypto APIs, it successfully discovered 679 crypto misuse issues in total, which on average costs only 1120 seconds per firmware. Our study shows 24.2% of firmware images violate at least one misuse rule, and most of the discovered misuses are unknown before. The misuses could result in sensitive data leakage, authentication bypass, password brute-force, etc. Our findings highlight the poor implementation and weak protection in today's IoT development.

The assistive technologies have been integrated into nearly all mainstream operating systems, which assist users with disabilities or difficulties in operating their devices. On Android, Google provides app developers with the accessibility APIs to make their apps accessible. Previous research has demonstrated a variety of stealthy attacks could be launched by exploiting accessibility capabilities (with BIND_ACCESSIBILITY_SERVICE permission granted). However, none of them systematically studied the underlying design of the Android accessibility framework, making the security implications of deploying accessibility features not fully understood. In this paper, we make the first attempt to systemically evaluate the usage of the accessibility APIs and the design of their supporting architecture. Through code review and a large-scale app scanning study, we find the accessibility APIs have been misused widely. Further, we identify a series of fundamental design shortcomings of the Android accessibility framework: (1) no restriction on the purposes of using the accessibility APIs; (2) no strong guarantee to the integrity of accessibility event processing; (3) no restriction on the properties of custom accessibility events. Based on these observations, we demonstrate two practical attacks - installation hijacking and notification phishing - as showcases. As a result, tens of millions of users are under these threats. The flaws and attack cases described in this paper have been responsibly reported to the Android security team and the corresponding vendors. Besides, we propose some improvement recommendations to mitigate those security threats.