Rediscovering Method Confusion in Proposed Security Fixes for Bluetooth

—Previous works have shown that Bluetooth is susceptible to so-called Method Confusion attacks. These attacks manipulate devices into conducting conflicting key establishment methods, leading to compromised keys. An increasing amount of security-sensitive applications, like payment terminals, organizational asset tracking systems and conferencing technologies now rely on the availability of a technology like Bluetooth. It is thus an urgent goal to find and validate a mitigation to these attacks or to provide an appropriate replacement for Bluetooth without introducing additional requirements that exclude device or user groups. Despite recent solution proposals, existing threat models overlook certain attack vectors or dismiss important scenarios and consequently suffer under new variants of Method Confusion. Wefirstpropose an extended threat model that appreciates the root issue of Method Confusion and also considers multiple pairing attempts and one-sided pairings as security risks. Evaluating existing solution proposals with our threat model, we are able to detect known Method Confusion attacks, and identify new vulnerabilities in previous solution proposals. We demonstrate the viability of these attacks on real-world Bluetooth devices. We further discuss a novel solution approach offering enhanced security, while maintaining compatibility with existing hardware and Bluetooth user behavior. We conduct a formal security proof of our proposal and implement it on commonplace Bluetooth hardware, positioning it as the currently most promising update proposal for Bluetooth.