  We present a simple yet potentially devastating and hard-to-detect threat,
called Gummy Browsers, whereby the browser fingerprinting information can be
collected and spoofed without the victim's awareness, thereby compromising the
privacy and security of any application that uses browser fingerprinting. The
idea is that attacker A first makes the user U connect to his website (or to a
well-known site the attacker controls) and transparently collects the
information from U that is used for fingerprinting purposes. Then, A
orchestrates a browser on his own machine to replicate and transmit the same
fingerprinting information when connecting to W, fooling W to think that U is
the one requesting the service rather than A. This will allow the attacker to
profile U and compromise U's privacy. We design and implement the Gummy
Browsers attack using three orchestration methods based on script injection,
browser settings and debugging tools, and script modification, that can
successfully spoof a wide variety of fingerprinting features to mimic many
different browsers (including mobile browsers and the Tor browser). We then
evaluate the attack against two state-of-the-art browser fingerprinting
systems, FPStalker and Panopticlick. Our results show that A can accurately
match his own manipulated browser fingerprint with that of any targeted victim
user U's fingerprint for a long period of time, without significantly affecting
the tracking of U and when only collecting U's fingerprinting information only
once. The TPR (true positive rate) for the tracking of the benign user in the
presence of the attack is larger than 0.9 in most cases. The FPR (false
positive rate) for the tracking of the attacker is also high, larger than 0.9
in all cases. We also argue that the attack can remain completely oblivious to
the user and the website, thus making it extremely difficult to thwart in
practice.
