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To: Mikhail Teterin <mi+mill@aldan.algebra.com>
References: <48ADA81E.7090106@aldan.algebra.com>
From: Christian Laursen <xi@borderworlds.dk>
Date: Thu, 21 Aug 2008 21:58:00 +0200
In-Reply-To: <48ADA81E.7090106@aldan.algebra.com> (Mikhail Teterin's message
	of "Thu\, 21 Aug 2008 13\:38\:38 -0400")
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Cc: freebsd-security@freebsd.org, freebsd-stable@FreeBSD.org
Subject: Re: machine hangs on occasion - correlated with ssh break-in
	attempts
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Mikhail Teterin <mi+mill@aldan.algebra.com> writes:

> A machine I manage remotely for a friend comes under a distributed ssh
> break-in attack every once in a while. Annoyed (and alarmed) by the
> messages like:
>
> Aug 12 10:21:17 symbion sshd[4333]: Invalid user mythtv from 85.234.158.180
> Aug 12 10:21:18 symbion sshd[4335]: Invalid user mythtv from 85.234.158.180
> Aug 12 10:21:20 symbion sshd[4337]: Invalid user mythtv from 85.234.158.180
> Aug 12 10:21:21 symbion sshd[4339]: Invalid user mythtv from 85.234.158.180
>
> I wrote an awk-script, which adds a block of the attacking IP-address
> to the ipfw-rules after three such "invalid user" attempts with:
>
>    ipfw add 550 deny ip from ip

I don't know if it will make your problem go away, but using ipfw
tables for this seems to be a better idea than creating a new rule for
every IP address.

So you just need one rule:

    ipfw add 550 deny ip from table(1)

And then when you want to add an IP address to the table:

    ipfw table 1 add <ip>

You can add ranges too using the CIDR notation.

-- 
Christian Laursen