full-disclosure - Re: SSH brute force blocking tool

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Message-ID: <20061128163242.GD31705@sdf.lonestar.org>
Date: Tue, 28 Nov 2006 16:32:42 +0000
From: Tavis Ormandy <taviso@...too.org>
To: Thierry Zoller <Thierry@...ler.lu>
Cc: full-disclosure <full-disclosure@...ts.grok.org.uk>
Subject: Re: SSH brute force blocking tool

On Tue, Nov 28, 2006 at 05:14:28PM +0100, Thierry Zoller 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).

openssh can be configured to log to btmp, I would suggest parsing this
file, it's format is documented in utmp(5).

I wouldnt use a shell script to do so, but I suppose you could use lastb
if you really wanted to, something like `lastb -ai ssh:notty | awk '{print $(NF)}'`.

I think increasing the codepaths that an unauthenticated attacker can
access is always going to be a bad idea, enforcing good password
policies via cracklib or jtr and just ignoring the minor irritation of
these automated attacks would be a safer bet.

Thanks, Tavis.

-- 
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taviso@....lonestar.org | finger me for my pgp key.
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