Re: [tram] Allow TURN to forward inbound connectivity checks without permission

Justin Uberti <juberti@google.com> Sun, 01 April 2018 22:09 UTC

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From: Justin Uberti <juberti@google.com>
Date: Sun, 01 Apr 2018 22:09:40 +0000
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To: Simon Perreault <sperreault@jive.com>
Cc: TirumaleswarReddy_Konda@mcafee.com, Brandon Williams <brandon.williams@akamai.com>, Nils Ohlmeier <nohlmeier@mozilla.com>, "Cullen Jennings (fluffy)" <fluffy@cisco.com>, Eric Rescorla <ekr@rtfm.com>, tram@ietf.org
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Subject: Re: [tram] Allow TURN to forward inbound connectivity checks without permission
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On Sun, Apr 1, 2018 at 9:56 AM Simon Perreault <sperreault@jive.com> wrote:

> 2018-03-31 18:50 GMT-04:00 Justin Uberti <juberti@google.com>om>:
>
>> As Brandon says, the ufrag/pwd info could be posted along with the
>> address of the server, so while this raises the bar, it doesn't solve the
>> problem.
>>
>> I agree with Brandon that the only reasonable way to completely contain
>> this is some sort of server policy, e.g., some time window or session count
>> after which the permission bypass expires, meaning that someone running a
>> server would have to be continually requesting new allocations and posting
>> their address/credentials.
>>
>
> Do we need to completely contain this? Is there actually a problem with
> the proposal?
>
> Allowing STUN in allows someone to run a server if and only if the
> protocol masquerades as STUN. It doesn't allow a user to run an arbitrary
> server. For this to be exploitable, the user would also need to control the
> clients in some way.
>
> I can't think of a way this could be exploited practically. Maybe I lack
> imagination?
>

I don't think this is fatal to the proposal. I just think that we need to
be up front that this is a potential loophole, and have some explicit
discussion in the document of how one might solve this problem should it
become necessary (e.g., with server policy).