[tbb-bugs] #16395 [Tor Browser]: Circuit isolation by SOCKS proxy may be breaking other proxies or non-proxies

[Tor Bug Tracker & Wiki]

#16395: Circuit isolation by SOCKS proxy may be breaking other proxies or non-
proxies
---------------------------------+--------------------------
 Reporter:  GigabyteProductions  |          Owner:  tbb-team
     Type:  defect               |         Status:  new
 Priority:  normal               |      Milestone:
Component:  Tor Browser          |        Version:
 Keywords:                       |  Actual Points:
Parent ID:                       |         Points:
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 If, for whatever reason, the user wants to disable the Tor Browser from
 connecting to their local Tor daemon (such as to prevent tor-through-tor
 with forced transparent torrification, or use the Tor Browser for it's
 security rather than it's anonymity, or point the Tor Browser to an SSH
 SOCKS proxy), they will find that since the release of the Tor Browser
 4.5.1, it will fail to connect to any SOCKS proxy that isn't a Tor daemon,
 and it will complain saying, "Firefox is configured to use a proxy server
 that can't be found." when proxies are disabled.

 I believe the cause of this issue is
 https://gitweb.torproject.org/torbutton.git/commit/?id=59445b7baed58e712bd38c02e6dc75882ff0c997
 or a related commit to the Tor Button. Disabling the Tor Button resolves
 the issue, but this isn't desired as the Tor Button provides additional
 protections such as the HTML5 canvas extraction.

 This can easily be recreated by having the 32-bit Linux package of the Tor
 Browser, and the attached 0000tor-use-system-4.5.2test.js file in the
 current directory, and then running something along the lines of:
 {{{
 xz -d < tor-browser-linux32-4.5.2_en-US.tar.xz | tar -xv
 cp 0000tor-use-proxy-4.5.2test.js tor-browser_en-
 US/Browser/TorBrowser/Data/Browser/profile.default/preferences/
 tor-browser_en-US/Browser/start-tor-browser --verbose
 }}}
 The above assumes there is a SOCKS5 proxy running on your machine on port
 1080. This can easily be done with something like
 {{{
 ssh -Dlocalhost:1080 localhost -N
 }}}

--
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/16395>
Tor Bug Tracker & Wiki <https://trac.torproject.org/>
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