One Side-Channel to Bring Them All and in the Darkness Bind Them: Associating Isolated Browsing Sessions

Online tracking and fingerprinting is becoming increasingly more prevalent and pervasive. The privacy threats associated with these practices have given rise to a wide variety of privacy-enhancing solutions. However, as these solutions retroactively apply patches to existing browsers in an attempt to thwart potential attacks, it is of key importance that the complete threat surface is known such that all risks can be considered. In this paper we evaluate the browser’s threat surface with regard to fingerprinting and tracking in the context of isolated browsing sessions, i.e. regular versus incognito sessions or sessions across different browsers. We uncover and evaluate three types of side-channels, and show how an adversary can exploit these to track users across sessions and even reveal the IP address of Tor users when they use a concurrent browsing session.