[Freeswitch-users] Your Security Best Practices

[Michael Collins]

On Thu, Jun 17, 2010 at 3:31 PM, Code Ghar <codeghar at gmail.com> wrote:

> I was reading up on some security advice and came across an article from
> Digium (http://blogs.digium.com/2009/03/28/sip-security/). A few points
> that stood out for me were:
>
> "Make your SIP usernames different than your extensions". This sounds like
> good advice because now an attacker has to guess the user name and password
> instead of just a password. The biggest benefit to this is that even if
> someone knows the format of your extension numbers, they are not able to use
> it for registration credentials. Of course, the issue of DoS using a large
> number of simultaneous authentication requests still remains. How can we
> deal with this?
>

Use fail2ban or some other mechanism. If someone is sending mass numbers of
SUBSCRIBEs then you should be handling that the same way you handle all
brute-force attacks - at the firewall. Although you should definitely not
make hacking your VoIP system easy, you should also keep in mind that
external security is an absolute must. Use the layered approach


>
> "... reject bad authentication requests on valid usernames with the same
> rejection information as with invalid usernames ..." How can we do this in
> FS? I haven't looked at this yet so maybe FS does such a thing anyways;
> advice from your experience and expertise required.
>
This I don't know. Is it handled down in Sofia? Brian or Tony could tell us.


>
> "Allow only one or two calls at a time per SIP entity, where possible."
> This is standard practice in prepaid phone card business. They allow only
> one simultaneous call and if you try to use the PIN to make another call
> it's not allowed. At the application level we may be able to do this in FS
> but it reminds me of another scenario. Let's say a user's registration is
> compromised. Can we prevent registration with same credentials from two
> different locations in FS? For example, one registration attempt is from New
> York and the other from Baltimore. This would affect the legitimate user
> because they might not be able to register. Does anyone restrict this way
> using FS?
>
I'm sure you could use a combination of ACLs and mod_limit.


>
> Apart from the article mentioned, there are some other issues, one of which
> is ANI authentication. A lot of pinless prepaid phone services use your
> caller ID to authenticate and authorize a call. you give them your phone
> number and when you call from there you can use the service. With VoIP it's
> very easy to spoof ANI. I believe the concept of "context" helps a lot here.
> Say you know the ANI's you assigned to your registered users. They would be
> in the "default" context, for example. Now if an attacker uses the same ANI
> but tries not from a registered endpoint but say from one of your carriers.
> His context would be "public", for example. This way the combination of ANI
> with context can prevent such attacks.
>
I cringe at the thought of doing *ANY* kind of authentication based on
incoming caller ID...


>
> But what if the authorized ANI (say 4145550000) is not from a registered
> endpoint but from a cell phone, similar to the pinless services offered
> today. In this scenario I think there's not much we can do. If we have given
> a user an access number (say 2125550000) provided to us by a DID provider,
> say ABC, then whenever someone dials 2125550000 then we get the call only
> through ABC, whom we have allowed. But we can't be sure that 4145550000 is
> actually 4145550000 and not someone pretending to be them. Has anyone
> figured out a way to detect and/or prevent such fraudulent calls? Is it even
> possible?
>
I think this is where mod_cleo comes in. :P Seriously, you probably should
treat inbound calls as untrusted regardless of where they're from, at least
until you've done some level of verification. A PIN code isn't hyper-secure,
but it is better than nothing.

You can't prevent all of these attacks. The best you can hope to do is to
make the attacks as difficult as reasonably possible without irritating your
paying customers.

I invite others to chime in. Also, I've started an informal security best
practices page on the wiki:

http://wiki.freeswitch.org/wiki/Security_bp

Everyone put your thoughts up and we'll formalize it at a later time.
-MC


>
>
>
> On Tue, Jun 15, 2010 at 4:59 PM, Anthony Minessale <
> anthony.minessale at gmail.com> wrote:
>
>> We have some parameters to disable some commonly abused features in a
>> carrier env.
>>
>> in the sofia profile
>>
>> set manage-presence to false
>>
>> If you are not providing registration or client transfers disable them
>> completely
>> set disable-transfer to true
>> set disable-register to true
>>
>>
>> And register for ClueCon where someone will probably give a talk on VoIP
>> security!
>>
>>
>> --
>> Anthony Minessale II
>>
>> FreeSWITCH http://www.freeswitch.org/
>>
>> ClueCon http://www.cluecon.com/
>> Twitter: http://twitter.com/FreeSWITCH_wire
>>
>> AIM: anthm
>> MSN:anthony_minessale at hotmail.com <MSN%3Aanthony_minessale at hotmail.com>
>> GTALK/JABBER/PAYPAL:anthony.minessale at gmail.com<PAYPAL%3Aanthony.minessale at gmail.com>
>> IRC: irc.freenode.net #freeswitch
>>
>> FreeSWITCH Developer Conference
>> sip:888 at conference.freeswitch.org <sip%3A888 at conference.freeswitch.org>
>> googletalk:conf+888 at conference.freeswitch.org<googletalk%3Aconf%2B888 at conference.freeswitch.org>
>> pstn:+19193869900
>>
>>
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