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

Justin Uberti <> Sun, 01 April 2018 22:09 UTC

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From: Justin Uberti <>
Date: Sun, 01 Apr 2018 22:09:40 +0000
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To: Simon Perreault <>
Cc:, Brandon Williams <>, Nils Ohlmeier <>, "Cullen Jennings (fluffy)" <>, Eric Rescorla <>,
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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 <> wrote:

> 2018-03-31 18:50 GMT-04:00 Justin Uberti <>:
>> 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).