'Scheme Flooding' Technique May Be Used To Deanonymize You

sandbagger shares a report from The Register: FingerprintJS, maker of a browser-fingerprinting library for fraud prevention, on Thursday said it has identified a more dubious fingerprinting technique capable of generating a consistent identifier across different desktop browsers, including the Tor Browser. Konstantin Darutkin, senior software engineer at FingerprintJS, said in a blog post that the company has dubbed the privacy vulnerability "scheme flooding." The name refers to abusing custom URL schemes, which make web links like "skype://" or "slack://" prompt the browser to open the associated application. "The scheme flooding vulnerability allows an attacker to determine which applications you have installed," explains Darutkin. "In order to generate a 32-bit cross-browser device identifier, a website can test a list of 32 popular applications and check if each is installed or not." Visiting the schemeflood.com site using a desktop (not mobile) browser and clicking on the demo will generate a flood of custom URL scheme requests using a pre-populated list of likely apps. A browser user would typically see a pop-up permission modal window that says something like, "Open Slack.app? A website wants to open this application. [canel] [Open Slack.app]." But in this case, the demo script just cancels if the app is present or reads the error as confirmation of the app's absence. It then displays the icon of the requested app if found, and moves on to its next query. The script uses each app result as a bit to calculate the identifier. The fact that the identifier remains consistent across different browsers means that cross-browser tracking is possible, which violates privacy expectations.

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