[OpenSIPS-Users] attack from friendly-scanner

SamyGo govoiper at gmail.com
Tue Oct 9 09:11:58 CEST 2012


Very nice suggestions by Brett. I remember there are regular thread like
these on the mailing lists and people share a lot of experiences. AFAIR
there was some service which contains the IP addresses of known attackers
available for users. OP needs to do some searching in this regard to
collect more ideas.

* Nothing is _NOT_ CPU cycles free *

I'm not sure about sip vicious but if I were to detect and hack a SIP
server I'd first start by sending OPTIONS on its ports. Mostly that's where
things kick off. Changing the user-agent field is nothing big, so question
is how do you know a hacker is about to get angry !!

I'd say it needs a time populated repository and a well crafted shell
script to maintain the list of Hacker IPs captured in the past and use it
across all the servers or devices. Let me explain the idea.

* ii)* - For any incoming packets one needs to look-up the hacker's listing
and detect if a known hacker or not.
 *i)* - Take fail2ban for example, or pike module , or iptables rate limit
mechanism to initially detect a new born hacker trying to access your sip
server (yes will take few minutes to finally conclude that a particular
source IP is hacker) - Store that IP in your hacker's listing.
*iii)* - Use an intelligent script to share the detected hacker's IP across
all the other SIP servers and router devices/firewall to block the traffic
at network layer.

*Critical Exceptions:*
Always ensure that the IP which is going to get blocked across the whole
network perimeter is not your own server or within the same subnet as
your's. It shouldn't be localhost as well.(Hint: IP spoofing)

*Focus on Security rather Friendly-scanner:*
One need to secure each and everything when it comes to security, just one
layer security  i.e fail2ban or iptables or pike module is never enough.
Like Brett said you can drop packets once detected a "very friendly
scanner", how about a customer who wants to toy with your service ! how
about a massive DoS attack !! drop() won't help alone. iptables needs to be
there to stop the packets from even reaching the SIP server app, then again
why should the server's NIC be chocked up by that massive DoS ! your
firewall or networking device should stop the packets from entering the
network !

This is just not enough: How about a different unique new tool which sends
malicious or malformed SIP packets to crash the server !! its just one
packet but malformed -- all the above measures WILL fail !! Obviously needs
to go one step ahead and use SNORT or anything like IDS+IPS to verify that
the packet going through the network is not malformed.

Thats pretty much it for now. There are things which I've forgotten to
write at the moment OR might not even know which I expect some one else may
like to add.

Networks and Data Security is a huge field, and VoIP security alone has
hundreds of book on the topic.

*Interesting threads to read: *
Read: http://blog.sipvicious.org/ to know more about the tool we all face
every once a while.
Fail2ban for openSIPS :: http://www.opensips.org/Resources/DocsTutFail2ban

Best Regards

On Mon, Oct 8, 2012 at 6:31 PM, Brett Nemeroff <brett at nemeroff.com> wrote:

> First of all,
> This is an attack from sipvicious. It is an *attack*. It will be very high
> rate (cps) and you do *not* want to use anything that consumes resources to
> attempt to block it.
> First recommendation is to use iptables. In addition, you *should* put a
> check in your config for friendly-scanner and drop() the packet. Do not
> reply with a sip code. You want to be invisible to the attacker. If you
> reply with a sip code, they'll just scan you attempting to find a request
> combination that will return a usable result.
> 1. Do whatever you can to not use CPU resources to block this
> 2. Don't look like a SIP server to source IPs you do not recognize
> I guarantee, if you look like a SIP server, you will get brutally attacked
> from unsolicited sources.
> Read up on the fail2ban docs for asterisk. They have some good ideas in
> there on how to perform intrusion detection and how to automatically add
> offending traffic to fail2ban. You can do something similar in OpenSIPs.
> I would be very curious to hear about other people's experiences using the
> Pike module to block this type of traffic. For what it's worth, I've seen
> attack traffic high enough in bandwidth to saturate a pretty beefy internet
> connection and I've even seen it crash routers. If you can avoid them
> finding you in the first place, that would be a much better option.
> -Brett
> On Mon, Oct 8, 2012 at 7:53 AM, Engineer voip <forvoip4 at gmail.com> wrote:
>> Hi,
>> I'm trying to use pike module and i'm using the script above, but when i
>> execute this command " opensipsctl fifo pike_list"
>> i don't get any address blocked
>> My opensips config is:
>> loadmodule "pike.so"
>> modparam("pike", "sampling_time_unit", 10)
>> modparam("pike", "reqs_density_per_unit", 30)
>> modparam("pike", "remove_latency", 120)
>> modparam("pike", "check_route","pike") # enable automatic checking
>> modparam("pike", "pike_log_level",1)
>> route[pike]
>> {
>>  if (src_ip==x.x.x.x ||src_ip==gw_ip) # Trusted IP
>>   xlog("L_INFO", "in pike route ");
>>   drop();
>> }
>> have you an idea please toresolve that?
>> 2012/10/8 SamyGo <govoiper at gmail.com>
>>> Hi,
>>> Relax it says its Friendly !!
>>> But still if you want to block it you've many options i.e in
>>> opensips.cfg start put a condition $ua =~ "friendly-scanner".  If matched
>>> return stateless some error.
>>> Other option is to use pike module.
>>> Another option is use fail2ban for opensips logs.
>>> More sophisticated options involve firewalls with IPS and IDS modules.
>>> I hope it was helpful.
>>> BR
>>> Sammy
>>>  On Oct 8, 2012 2:33 PM, "Engineer voip" <forvoip4 at gmail.com> wrote:
>>>> Hi All,
>>>> I receveid several packets of registration from a  "friendly-scanner"
>>>> on my opensips server
>>>> how can i do to block that please??
>>>> --
>>>> Best Regards.
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>> --
>> Best Regards.
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