Hello,

checking the IP in the Via headers can be done in config file using a while loop:

$var(i) = 0;

while($(hdr(Via)[$var(i)])!=$null) {
   # use transformations to extract the IP in $(hdr(Via)[$var(i)]) and test it against $Ri
   ...
   $var(i) = $var(i) + 1;
}

Also, checking the max-breadth should be possible in config file -- iirc, Olle played with it at one of the SIPit events I attended, maybe he can add more details here. I haven't read the RFC 5393 to be able to provide an example here.

If someone wants to add a module to simplify the config, he/she is welcome to do it.

Cheers,
Daniel

On 21/10/15 10:35, Guillaume wrote:

Hi guys,

What do you think about the RFC 5393 on loop detection and amplification attack protection?

The RFC is short and still a proposed standard but don't you think it could be useful to prevent loop and amplification attack? Because even if the max-forward field reduces the loop to ~70 hosts (in most cases) with some techniques we could fork the message up to 2^70 messages (as described in the RFC) to crash the servers.

Basically the server has to do 2 things:
* check if it is not already in the via of the message
* the previous check is not enough as a B2BUA could have replace the via headers, so the RFC introduces a new field called max-breadth to limit the forking.

I have not seen a lot of implementation of this RFC on the free SIP software and I think it could be a good way to improve kamailio making a module for it (the easier way to implement this feature I think).

In fact I'm in a research internship about VoIP security and I have time to develop such a module for kamailio if you think it's a good idea (I'm looking for some security improvements in free software solutions so if you have other idea don't hesitate to tell me).

Cheers,

Tetram
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