Since the attacker controls the website, they can force the browser to visit subdomains without any user interaction. Accordingly, a set of N-subdomains can be used to create an N-bit identifier, that is unique for each browser. These subdomains serve different favicons and, thus, create their own entries in the Favicon-Cache.
Firefox hacking sites series#
To be more precise, this tracking can be easily performed by any website by redirecting the user accordingly through a series of subdomains. Specifically, websites can create and store a unique browser identifier through a unique combination of entries in the favicon cache. Advertisementīy leveraging all these properties, we demonstrate a novel persistent tracking mechanism that allows websites to reidentify users across visits even if they are in incognito mode or have cleared client-side browser data. With tweaks, websites can reduce the delay. That would add about 2 seconds to the time it takes for the final page to load. To be able to track 4.5 billion unique browsers, a website would need 32 redirections, since each redirection translates to 1 bit of entropy. The number of redirections required varies depending on the number of unique visitors a site has. Websites can exploit the new favicon side channel by sending visitors through a series of subdomains-each with its own favicon-before delivering them to the page they requested. In response, some browsers have attempted to curb the tracking by blocking fingerprinting scripts. Device fingerprinting can work even when people use multiple browsers. A 2013 study found that 1.5 percent of the world’s most popular sites employed the technique.
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Firefox hacking sites software#
Advertisementįurther Reading Now sites can fingerprint you online even when you use multiple browsersOne of those methods is known as device fingerprinting, a process that collects the screen size, list of available fonts, software versions, and other properties of the visitor's computer to create a profile that is often unique to that machine. Firefox would also be susceptible to the technique, but a bug prevents the attack from working at the moment. The attack works against Chrome, Safari, Edge, and until recently Brave, which developed an effective countermeasure after receiving a private report from the researchers. To make matters worse, the idiosyncratic caching behavior of modern browsers, lends a particularly egregious property to our attack as resources in the favicon cache are used even when browsing in incognito mode due to improper isolation practices in all major browsers. The attack workflow can be easily implemented by any website, without the need for user interaction or consent, and works even when popular anti-tracking extensions are deployed. “Overall, while favicons have long been considered a simple decorative resource supported by browsers to facilitate websites’ branding, our research demonstrates that they introduce a powerful tracking vector that poses a significant privacy threat to users,” the researchers wrote.
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Websites can abuse this arrangement by loading a series of favicons on visitors’ browsers that uniquely identify them over an extended period of time. Researchers from the University of Illinois, Chicago said in a new paper that most browsers cache the images in a location that’s separate from the ones used to store site data, browsing history, and cookies. The technique leverages the use of favicons, the tiny icons that websites display in users’ browser tabs and bookmark lists. Now, websites have a new way to defeat all three. The prospect of Web users being tracked by the sites they visit has prompted several countermeasures over the years, including using Privacy Badger or an alternate anti-tracking extension, enabling private or incognito browsing sessions, or clearing cookies.