[asterisk-users] Interesting attack tonight & fail2ban them

[Michelle Dupuis]

I happened to be in the cli tonight as some (208.122.57.58) initiated a simple attack - just trying to make long distance calls from outside context.  Although harmless, this went on for several minutes as the idiot just used up my bandwidth with SIP messages.  Here's and example:

[2011-12-28 22:53:42] NOTICE[9635]: chan_sip.c:14035 handle_request_invite: Call from '' to extension '6442032987219' rejected because extension not found.
[2011-12-28 22:53:44] NOTICE[9635]: chan_sip.c:14035 handle_request_invite: Call from '' to extension '7442032987216' rejected because extension not found.
[2011-12-28 22:53:46] NOTICE[9635]: chan_sip.c:14035 handle_request_invite: Call from '' to extension '8442032987216' rejected because extension not found.
[2011-12-28 22:53:48] NOTICE[9635]: chan_sip.c:14035 handle_request_invite: Call from '' to extension '008442032987215' rejected because extension not found.
[2011-12-28 22:53:50] NOTICE[9635]: chan_sip.c:14035 handle_request_invite: Call from '' to extension '007442032987218' rejected because extension not found.
[2011-12-28 22:53:52] NOTICE[9635]: chan_sip.c:14035 handle_request_invite: Call from '' to extension '006442032987219' rejected because extension not found.
[2011-12-28 22:53:54] NOTICE[9635]: chan_sip.c:14035 handle_request_invite: Call from '' to extension '005442032987216' rejected because extension not found.
[2011-12-28 22:53:56] NOTICE[9635]: chan_sip.c:14035 handle_request_invite: Call from '' to extension '004442032987250' rejected because extension not found.

I thought that it might be worth adding a line to my fail2ban filter, but am looking for a hand with the regex.  I have come up with:
            NOTICE.* .*: Call from '' to extension '.*' rejected because extension not found

but I realize that anyone misdialling a valid extension a few times gets cut off. Can someone suggest an improvement?  (How could I limit this to 4 or more digits dialled for example?)

Thanks!
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