[tbb-dev] MOZ_DISABLE_NONLOCAL_CONNECTIONS

[Nicolas Vigier]

On Thu, 15 Mar 2018, Tom Ritter wrote:

> 45 seconds ago I just learned about the environment variable
> MOZ_DISABLE_NONLOCAL_CONNECTIONS that we use in our testing
> environment. It feeds through to one real location in the browser:
> nsSocketTransport2
> https://searchfox.org/mozilla-central/rev/8976abf9cab8eb4661665cc86bd355cd08238011/netwerk/base/nsSocketTransport2.cpp#1297
> 
> This isn't a sandbox. If an attacker has code execution (parent or
> content process) they can make network connections manually from
> system libraries and will never touch this code. But it might be a way
> to add (some) assurance about browser features accidentally bypassing
> the proxy.
> 
> So I'm wondering if this is something Tor Browser can set for defense
> in depth. In fact, it's already in esr52:
> https://dxr.mozilla.org/mozilla-esr52/search?q=AreNonLocalConnectionsDisabled
>  I tried to get Tor Browser to unset the proxy but couldn't seem to
> get it to work; is there a patch that prevents this?

Even if it doesn't add a lot of protection, it doesn't cost a lot to
enable it, so it sounds like a good idea.

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