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It's very easy to disregard this message, but I think this is something
VERY IMPORTANT that we should be talking about much more -- especially
for those deploying systems for remote workers over a public network.
There is a huge opportunity for toll fraud, voip spam, and such as this
market segment continues to grow.
Lability becomes an issue too -- who's responsible when someone is
defrauded via your phone system? The phone companies have a record of you
calling so-and-so; can you prove you didn't?
These are the sort of scans I've been spotting hitting some of my systems
the past week, trying to brute force. You'll see incremental scans like:
[Nov 5 19:58:30] NOTICE[19408] chan_sip.c: Registration from '"0"<sip:[EMAIL
PROTECTED]>' failed for 'EE.FF.GG.HH' - No matching peer found
...
[Nov 5 20:20:21] NOTICE[19408] chan_sip.c: Registration from '"1000"<sip:[EMAIL
PROTECTED]>' failed for 'EE.FF.GG.HH' - Wrong password
...
We were discussing this around the office, particularly how sipvicious
(http://sipvicious.org) works, and it was noted that you can find active
SIP accounts easily, and then start a brute force against a known active
account.
I poked my head into #asterisk-dev, and asked if there were a feature in
the works to automatically disable accounts after a number of bad auth
attempts. It's been discussed, but so far no code.
There are however some easy things you can do that are common across
running any service on the internet.
Inside of asterisk, you can cut down on your exposure by only allowing
particular SIP accounts to be registered from remotely by putting
deny-based ACL's on the other accounts, listing your local subnets as
permissable:
sip.conf
[somepeer]
type=peer
deny=0.0.0.0/0.0.0.0
permit=192.168.0.0/255.255.255.0
You can also create automatic blacklisting of IP addresses that attempt
too many SIP authentications per interval, such as this SSH example:
http://www.mattiasholm.com/node/6
Thoughts? What are other people doing to protect their exposure?
re,
spd
On Mon, 10 Nov 2008, Andre Courchesne - Consultant wrote:
Hi,
Just to let you know that I see a proliferation is SIP hack attempts. Twice
today I happened to be logged in servers where I saw SIP discovery from IP
212.12.148.109 and on the other server that same IP had actually gained
controlled of a SIP account (which was created with a weak secret by the
administrator).
The call pattern indicated that calls were made by a dialer of some sort
and the SIP packets were originating from an Asterisk server.
So be carefull about your server that you have to let unprotected on an
internet segment.
Andre
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