[tbb-bugs] #30531 [Applications/Tor Browser]: WebGL antialiasing support enabled iff. OpenGL is supported

Tor Bug Tracker & Wiki blackhole at torproject.org
Sat May 18 12:52:43 UTC 2019

#30531: WebGL antialiasing support enabled iff. OpenGL is supported
     Reporter:  intrigeri                 |      Owner:  tbb-team
         Type:  defect                    |     Status:  new
     Priority:  Medium                    |  Milestone:
    Component:  Applications/Tor Browser  |    Version:
     Severity:  Normal                    |   Keywords:  AffectsTails
Actual Points:                            |  Parent ID:
       Points:                            |   Reviewer:
      Sponsor:                            |
 With Tor Browser 8.5-build2, we see 2 different WebGL fingerprints on
 panopticlick: 2ef68bcd75e09a41aea04bae556f3ecc on bare metal and in VMs
 that support OpenGL acceleration, f9a0f737691a9b57f5294121fc58a2df in VMs
 that don't support OpenGL acceleration.

 Quoting segfault (from
 https://redmine.tails.boum.org/code/issues/16337#note-61) who investigated
 this further:

 "I looked at the JS code used by panopticlick to calculate this hash, and
 printed the values which go into the hash. The only difference I could
 find is that antialiasing is enabled iff OpenGL is enabled. (That's
 exposed via the antialias bool of gl.getContextAttributes(), see

 Impact: 1 bit of fingerprinting; risk: nowadays I would assume the huge
 majority of bare metal systems that can run TB have OpenGL, but most VMs
 haven't (unless geeky configuration is done, which is a minority). So it's
 roughly equivalent to splitting the anonymity set between VMs and bare
 metal, I'd say.

 GeKo says:

 > i guess we could think about making the antialiasing info uniform
 > like, just saying "no"

Ticket URL: <https://trac.torproject.org/projects/tor/ticket/30531>
Tor Bug Tracker & Wiki <https://trac.torproject.org/>
The Tor Project: anonymity online

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