Pierluigi Paganini March 10, 2016

A security researcher has devised a new technique to track users by analyzing the mouse movements, even when surfing on the Tor network.

While we surf on the Internet we leave an impressive amount of traces that could be used to track our profile and also reveal our identity even we are visiting resources in the darknet.

The way a user moves writes a blog post or moves a mouse could allow to track him.

The security researcher Jose Carlos Norte (@jcarlosnorte) has elaborated a technique relying on Javascript to create a unique fingerprint of internet users that could be used to track users while accessing the Tor network.

“While preventing users IP address to be disclosed is a key aspect for protecting their privacy, a lot of other things need to be taken into consideration. Tor browser is preconfigured to prevent a lot of possible attacks on user privacy, not only the communications layer provided by tor itself.” wrote Jose Carlos Norte.

“One common problem that tor browser tries to address is user fingerprinting. If a website is able to generate a unique fingerprint that identifies each user that enters the page, then it is possible to track the activity of this user in time, for example, correlate visits of the user during an entire year, knowing that its the same user. Or even worse, it could be possible to identify the user if the fingerprint is the same in tor browser and in the normal browser used to browse internet. It is very important for the tor browser to prevent any attempt on fingerprinting the user.”

The researcher explained that his Javascript code, once deployed on a website, could fingerprint a user based on how he moves the mouse. The researcher explained that observing user’s movements in a ‘significant’ number of pages the user visits on the clear web it is possible to create a unique fingerprint that can allow his identification even when he is in the Tor network.

The expert created a quick and dirty PoC called UberCookie to demonstrate that is possible to fingerprint a user in a controlled environment.

Norte explained that the most interesting fingerprinting vector he discovered on Tor Browser is getClientRects that allows to get the exact pixel position and size of the box of a given DOM element.

The results of the getClientRects call depend on multiple factors, including the resolution and the font configuration that can compose the fingerprinting vector.

Lorenzo Bicchierai from MotherBoard tried to contact members of the Tor Project and is still waiting for a reply.

“The Tor Project did not respond to a request for comment, but it seems that its developers are looking into this issue, according to two official bug reports. ” wrote Bicchierai.

The popular cyber security expert Mikko Hypponen published a Tweet that define “clever” the technique.

Clever! Fingerprinting a website user based on his mouse wheel moves, as reported by your browser. Has a demo, too. https://t.co/0MDkmpfxc5

— Mikko Hypponen (@mikko) 8 Marzo 2016

To avoid beign tracked with this fingerprint technique users can deactivate Javascript completely.

Pierluigi Paganini

(Security Affairs – Tor network, fingerprint)