Subject: RE: [SIP] How to stop a Lawnmower Man attack?

From: "Fox, Mike" <[email-masked]>
Date: Fri, 21 Jul 2000 10:15:49 -0700

Oops I need correct one sentence...
>> I would like to be clear in that I'm not trying to suggest 
>> that SIP does [ NOT ] support administrative control. 

>    I don't see how the protocol itself can help. I can
>    see pretty simple call gapping measures at proxies,
>    etc, help though but those don't require any new
>    protocol mechanisms. Also: a UAS can always insist
>    that the initial INVITE come through a trusted 
>    proxy rather than directly from the UAC. Assuming
>    that proxies are more trustworthy because they at
>    least have some admin behind them, you could limit
>    the zombie attack as above.

In other words a Gate Keeper. This is my conclusion too, but so far there is
no GK element proscribed for SIP, why not? Others must have come to a
different conclusion. The nature of the SIP/SDP will allow many flavors of
attack. This is not the protocol's problem, but the issue does need to be
addressed. I have not seen much public discussion in the way of threat
analysis with regard to these issues from the the SIP comunity. I hope
somewhere (perhaps ETSI/TIPHON WG 8) someone will give these issues deeper
consideration.

Best regards,
Mike

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---

From: Jonathan Rosenberg <[email-masked]>
Date: Sun, 23 Jul 2000 01:31:39 -0400

"Fox, Mike" wrote:
> no GK element proscribed for SIP, why not?

There is no need to define an additional element, or standardize
interfaces or protocols for it. This role can be played by a proxy. I
suspect, in fact, there are many ingenious ways you can build logic into
a proxy to prevent such attacks - call setup rate thresholds, etc.
Leaving these to the imaginations of implementors as a source of vendor
differentiation, rather than standardizing them in a protocol document,
seems a better way to go. 

That said, I do agree it would be nice to have a document that describes
the threats in a SIP system, with some discussions on protocol
mechanisms that might exist to alleviate them. This would be an
informational document. It was my hope that the security task force
(which has been a bit quiet as of late) would generate such a thing.

-Jonathan R.
-- 
Jonathan D. Rosenberg                       72 Eagle Rock Ave.
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