Most modern browsers—such as Chrome, Firefox, and Edge, and even browsers such as FuzzyFox and DeterFox (different, security-focused versions of Firefox)—have vulnerabilities that allow hosts of malicious websites to extract hundreds to thousands of URLs in a user’s web history, per new research from the University of California San Diego.
What’s worse, the vulnerabilities are built into the way they structure links, meaning that major structural changes will have to take place in these browsers in order to protect user privacy. The only browser that was immune to the attacks was Tor Browser, as the browser does not keep track of a user’s internet history.
As outlined in the UC San Diego report, this sniffing could happen in a couple of ways: they could force the browser to reload multiple complex images or image transformations that differ based on whether you’ve visited a link or not, which would create drastic differences in the loading time for each. With this strategy, actors can test 60 sensitive URLs per second.
In Google Chrome, the actor could also exploit what’s called a bytecode cache, which speeds up the loading time for revisiting a link that you’ve already visited. By embedding a special script in a web page, the actor can test how long it takes for a web page to load and infer whether you’ve visited it or not. Actors can probe 3,000 URLs per second with this method. But when the researchers reported the vulnerability to Google, the company marked the issue as “security-sensitive” but “low-priority.”