A Study of MAC Address Randomization in Mobile Devices and When it Fails

TLDR

MAC address randomization is a privacy technique that rotates random hardware addresses to hide device traffic and location, but its adoption varies across manufacturers. The authors conduct the first large‑scale study of MAC randomization, breaking down techniques by OS, manufacturer, and model, and identify multiple implementation flaws that can be exploited. They analyze device traffic, extend passive identification methods, and examine low‑level control frames to uncover a chipset flaw affecting all tested devices. They find that many devices send their true address instead of a randomized one, that passive attacks defeat randomization in about 96 % of Android phones, and that an active attack can track any device under certain conditions.

Abstract

Abstract Media Access Control (MAC) address randomization is a privacy technique whereby mobile devices rotate through random hardware addresses in order to prevent observers from singling out their traffic or physical location from other nearby devices. Adoption of this technology, however, has been sporadic and varied across device manufacturers. In this paper, we present the first wide-scale study of MAC address randomization in the wild, including a detailed breakdown of different randomization techniques by operating system, manufacturer, and model of device. We then identify multiple flaws in these implementations which can be exploited to defeat randomization as performed by existing devices. First, we show that devices commonly make improper use of randomization by sending wireless frames with the true, global address when they should be using a randomized address. We move on to extend the passive identification techniques of Vanhoef et al. to effectively defeat randomization in ~96% of Android phones. Finally, we identify a previously unknown flaw in the way wireless chipsets handle low-level control frames which applies to 100% of devices we tested. This flaw permits an active attack that can be used under certain circumstances to track any existing wireless device.