[Freeswitch-users] INVITE DoS Prevention

Ken Rice krice at freeswitch.org
Mon Feb 21 09:39:12 MSK 2011

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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