Rascals are always sociable, and the chief sign that a man has any nobility in his character is the little pleasure he takes in others company. Arthur Schopenhauer

We demonstrate how targeted deanonymization attacks performed via the CPU cache side channel can circumvent browser-based defenses. The attack framework we show is able to overcome the limitations of prior work, such as assumptions on the existence of cross-site leaks. As a result of this attack, the attacker is able to learn whether a specific individual visits the attacker-controlled website – a potentially serious privacy violation.

When a user visits the attacker-controlled website, the website uses an iframe, popunder, or tabunder to request a resource from a third-party website (i.e., the “leaky resource”). The response to this request, as well as the cache activity it generates in the user’s system, differs depending on the user state on the third-party website. An attacker monitoring the CPU cache side channel can analyze the cache patterns and learn whether the leaky resource was loaded successfully in the browser or not, and use this information to learn the identity of the visiting user. The attack can be scaled to identify thousands of users. Targeted Deanonymization via the Cache Side Channel: Attacks and Defenses