[tbb-bugs] #17446 [Tor Browser]: Canvas image extraction prompt logic

Tor Bug Tracker & Wiki blackhole at torproject.org
Thu Oct 29 19:12:35 UTC 2015

#17446: Canvas image extraction prompt logic
 Reporter:  arthuredelstein     |          Owner:  tbb-team
     Type:  defect              |         Status:  new
 Priority:  Medium              |      Milestone:
Component:  Tor Browser         |        Version:
 Severity:  Normal              |     Resolution:
 Keywords:  tbb-fingerprinting  |  Actual Points:
Parent ID:                      |         Points:
  Sponsor:                      |

Comment (by arthuredelstein):

 Replying to [comment:1 mcs]:
 > Replying to [ticket:17446 arthuredelstein]:
 > > Is there a reason we are preventing third parties from requesting
 permission on behalf of the first party?
 > When the canvas prompt was first added, there were too many prompts.
 See #7265.
 > > My feeling is we should either (a) allow third parties to request
 permission to extract canvas data, but assign that permission to the first
 party, or (b) prevent third parties from extracting canvas data at all.
 > I think (a) results in too many prompts. I think you have found a
 problem though: because the first party permission check is done first, if
 permission is ever granted for a page then all third party access is
 allowed. I am in favor of (b) but I do not know if that would break any
 sites that use canvas in a legitimate, non-fingerprinting way.

 I guess any third-party canvas extractions broken under (b) are also
 already broken by the current patch, unless that domain has previously
 been given permission as a first-party domain. This seems like an
 undesirable bit of linkability anyhow.

Ticket URL: <https://trac.torproject.org/projects/tor/ticket/17446#comment:2>
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