full-disclosure - Re: SSH brute force blocking tool

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Message-ID: <242a0a8f0611280933j13ed2bb1q6c2808ef2c4b29a6@mail.gmail.com>
Date: Tue, 28 Nov 2006 12:33:53 -0500
From: "Brian Eaton" <eaton.lists@...il.com>
To: full-disclosure <full-disclosure@...ts.grok.org.uk>
Subject: Re: SSH brute force blocking tool

(Resending since this somehow didn't make it to the list the first
time.  Apologies if you receive two copies.)

On 11/28/06, Thierry Zoller <Thierry@...ler.lu> wrote:
> Dear Tavis,
>
> TO> J, you have made an attempt to fix it, but is is not sufficient.
> TO> An attacker can still add arbitrary hosts to the deny list.
>
> Can you propose a fix ? Apart from the aggressivness of this thread
> I find it interesting to read (from a tech standpoint).

Unlike Tavis, I haven't had the guts to actually install and test this
little contraption.  But it looks like setting the sshd config option
"UseDNS no" might help.  Then sshd will log the client IP instead of
the client hostname, and you no longer need to rely on the attacker's
DNS to tell you which IP to blacklist.

Someone could still purposefully trigger a ban of an IP address they
controlled, but I don't think they could do arbitrary IPs any longer.

Regards,
Brian

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