Formal Model-Driven Discovery of Bluetooth Protocol Design Vulnerabilities

The Bluetooth protocol suite, including Bluetooth Classic, Bluetooth Low Energy, and Bluetooth Mesh, has become the de facto standard for short-range wireless communications. While formal methods have been applied to Bluetooth security, existing efforts either focus on one configuration of a protocol or one protocol of the suite, without considering other configurations or interactions among protocols. As a result, manual analysis still dominates the state-of-the-art security research of Bluetooth specification. To enable automatic Bluetooth security analysis with formal guarantees, we propose a comprehensive formal model for Bluetooth protocol suite covering both the key sharing phase and the data transmission phase, in all the three Bluetooth protocols, and detecting their design flaws automatically. Our formal model, written in ProVerif, adopts a modular design by abstracting each step within a protocol into an interface and implementing different methods in each step as modules to instantiate the interface, through which all possible configurations of a protocol could be examined. We further abstract different Bluetooth protocols into modules enabling the modeling of their interactions and relax the threat model to allow reasoning about semi-compromised devices. We use this model to formally verify 418 security properties and find 82 violations with attack examples capturing 5 known vulnerabilities and discovering 2 new security issues. Bluetooth SIG confirmed our independent discovery of these 2 new issues, with one issue assigned a CVE and the other issue acknowledged in a security notice. Our model provides one step towards formally verified Bluetooth security.