[Freeswitch-users] INVITE DoS Prevention

[Spencer Thomason]

After tinkering with it, I think that might be the best way.  The  
iptables method is cool but I'd like to have more dynamic control and  
with Fail2Ban looking at the challenges you could specifically ignore  
certain high traffic IPs and block others.  What would be very cool is  
if instead of logging every challenge, a log entry was written if  
there was a high number from a specific IP, then you could decide what  
to do about it with fail2ban, similar to the pike module for opensips  
does.


On Feb 21, 2011, at 1:31 AM, covici at ccs.covici.com wrote:

> I would change sip auth failure to challenge and then have sufficient
> times to only block if there are too many challenges in a certain  
> time.
> I am not even sure the failure works any more in recent gits.
>
> Spencer Thomason <spencer at 5ninesolutions.com> wrote:
>
>> Yes, that works great if they respond to the challenge with a failed
>> auth. But the scenario I'm trying to prevent is if they just send the
>> INVITE and never respond to the challenge.  Fail2Ban will not work as
>> every endpoint will initially send an INVITE and receive a challenge.
>> Legit calls will then respond correctly and not be logged as a SIP
>> auth failure but every call that is challenged will show up as SIP
>> auth challenge in the logs so there is no regex to differentiate
>> between legit an non legit traffic.
>>
>> Spencer
>>
>> On Feb 20, 2011, at 10:39 PM, Ken Rice wrote:
>>
>>> Fail2Ban ... This is block an IP with too many failed attempts from
>>> something like SipVicious pretty quickly
>>>
>>>
>>> On 2/20/11 11:07 PM, "Spencer Thomason" <spencer at 5ninesolutions.com>
>>> wrote:
>>>
>>>> Hi,
>>>> We run hosted Freeswitch instances in VMs with the internal profile
>>>> on
>>>> port 5060 connecting to clients mostly behind NAT and then the
>>>> external profile connecting to our proxies only.  Protecting the
>>>> external profile its straightforward.. we only allow traffic to/ 
>>>> from
>>>> our proxies at the firewall level.  But protecting the internal
>>>> profile seems to be a bit more difficult because the UACs could be
>>>> theoretically anywhere on the network.
>>>>
>>>> I'm currently using Fail2Ban to prevent brute force registration  
>>>> and
>>>> INVITEs on auth failures, e.g.:
>>>> failregex = \[WARNING\] sofia_reg.c:\d+ SIP auth failure \ 
>>>> (REGISTER\)
>>>> on sofia profile \'\w+\' for \[.*\] from ip <HOST>
>>>>            \[WARNING\] sofia_reg.c:\d+ SIP auth failure \(INVITE\)
>>>> on sofia profile \'\w+\' for \[.*\] from ip <HOST>
>>>>
>>>> My question is, since its part of a normal SIP dialog to challenge
>>>> the
>>>> INVITE, is there any way to prevent a possible DoS from just sheer
>>>> volume of incoming INVITEs on an Internet facing server
>>>> automatically.  I.e., If you block the logged challenge, you'd  
>>>> block
>>>> all legitimate INVITEs and registrations.  Since its UDP traffic I
>>>> couldn't come up with a way to do it automatically at the iptables
>>>> level. i.e. number of concurrent connections.  Is there some option
>>>> to
>>>> just not respond if a client is sending a number of requests over a
>>>> certain threshold?  It might not stop them from sending the traffic
>>>> but pretty soon they'd get the idea that it wasn't going to go
>>>> anywhere.  My concern is say there are 50 Freeswitch instances on a
>>>> box (albeit 8 core, 32GB ram, 8 15K raid 10 storage) and someone
>>>> starts sending thousands of rouge INVITEs to every VM on a physical
>>>> box that the CPU load from just challenging the incoming INVITEs
>>>> would
>>>> create a DoS.  We the logs regularly to try to catch people doing
>>>> this
>>>> sort of thing and drop them at a router upstream of the core  
>>>> network,
>>>> but I'd like to have it happen without human intervention.  Have I
>>>> completely over thought this and am missing something obvious?
>>>>
>>>> Thanks,
>>>> Spencer
>>>>
>>>>
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>>>
>>>
>>>
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>>
>>
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>
> -- 
> Your life is like a penny.  You're going to lose it.  The question is:
> How do
> you spend it?
>
>         John Covici
>         covici at ccs.covici.com
>
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