full-disclosure - Re: Distributed SSH username/password brute forceattack

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Date: Tue, 23 Oct 2007 19:11:40 -0500
From: nocfed <nocfed@...il.com>
To: full-disclosure@...ts.grok.org.uk
Subject: Re: Distributed SSH username/password brute
	forceattack

On 10/22/07, Anders B Jansson <hdw@...listi.se> wrote:
> A.L.M.Buxey@...ro.ac.uk wrote:
> > Hi,
> >
> >> Oct 22 20:36:13 nms sshd[90657]: Failed password for invalid user gopher
> >> from 77.46.152.2 port 55120 ssh2
> >
> > user/password authentication for SSH?  one way of cleaning up your
> > logs and killing this type of attack is to reconfigure your OpenSSH
> > to only allow key based logins. stopped my 10M+ logfiles straight away
>
> An even better way is to punt the attackers to a 'silent drop' table in your firewall.
>
> Cuts your logs to nothing and keeps the kiddies wasting their time.
>
> The latest attack surge is either directed or a bit more clever, haven't seen anything on my random user DSL traps.
> --
> // hdw
>

I still say to throw them into a TARPIT table and tag their
connections to throw them into a nice TCP window size of 0.  Currently
I lower unknown connections window size to bring them to a crawl while
known ranges immediately go through.  It's not about blocking all
unknown, but about making the process take up more of their resources.
 A silent drop will take up very little of the worm's time when
compared to a tarpit that can eat up minutes(hours if they do not set
timeouts) per connection.

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