From owner-freebsd-questions@FreeBSD.ORG Mon Jan 11 15:59:55 2010 Return-Path: Delivered-To: freebsd-questions@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id B2BA21065676 for ; Mon, 11 Jan 2010 15:59:55 +0000 (UTC) (envelope-from mexas@bristol.ac.uk) Received: from dirg.bris.ac.uk (dirg.bris.ac.uk [137.222.10.102]) by mx1.freebsd.org (Postfix) with ESMTP id 6FA8D8FC1C for ; Mon, 11 Jan 2010 15:59:55 +0000 (UTC) Received: from seis.bris.ac.uk ([137.222.10.93]) by dirg.bris.ac.uk with esmtp (Exim 4.69) (envelope-from ) id 1NUMgJ-0006kx-CH; Mon, 11 Jan 2010 15:59:54 +0000 Received: from mech-cluster241.men.bris.ac.uk ([137.222.187.241]) by seis.bris.ac.uk with esmtp (Exim 4.67) (envelope-from ) id 1NUMgI-0000aB-9J; Mon, 11 Jan 2010 15:59:50 +0000 Received: from mech-cluster241.men.bris.ac.uk (localhost [127.0.0.1]) by mech-cluster241.men.bris.ac.uk (8.14.3/8.14.3) with ESMTP id o0BFxoQZ061873; Mon, 11 Jan 2010 15:59:50 GMT (envelope-from mexas@bristol.ac.uk) Received: (from mexas@localhost) by mech-cluster241.men.bris.ac.uk (8.14.3/8.14.3/Submit) id o0BFxnHn061872; Mon, 11 Jan 2010 15:59:49 GMT (envelope-from mexas@bristol.ac.uk) X-Authentication-Warning: mech-cluster241.men.bris.ac.uk: mexas set sender to mexas@bristol.ac.uk using -f Date: Mon, 11 Jan 2010 15:59:49 +0000 From: Anton Shterenlikht To: Matthew Seaman Message-ID: <20100111155949.GA61863@mech-cluster241.men.bris.ac.uk> References: <20100111140105.GI61025@mech-cluster241.men.bris.ac.uk> <4B4B42D0.9070101@infracaninophile.co.uk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4B4B42D0.9070101@infracaninophile.co.uk> User-Agent: Mutt/1.5.20 (2009-06-14) X-Spam-Score: -1.5 X-Spam-Level: - Cc: Anton Shterenlikht , freebsd-questions@freebsd.org Subject: Re: denying spam hosts ssh access - good idea? X-BeenThere: freebsd-questions@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: User questions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 11 Jan 2010 15:59:55 -0000 On Mon, Jan 11, 2010 at 03:25:04PM +0000, Matthew Seaman wrote: > Anton Shterenlikht wrote: > > I'm thinking of denying ssh access to host from which > > I get brute force ssh attacks. > > > > HOwever, I see in /etc/hosts.allow: > > > > # Wrapping sshd(8) is not normally a good idea, but if you > > # need to do it, here's how > > #sshd : .evil.cracker.example.com : deny > > > > Why is it not a good idea? > > Probably because ssh is likely to be the only method of login access > you have to a remote server, and hosts.allow could conceivably be spoofed > into blocking your legitimate access? In any case, hosts.allow is a poor relation to using a real firewall -- it has no access to the lower level bits > of the networking code, so has to allow a full tcp connection setup before it > can block anything. Some daemons allow quite a lot of interaction with the > remote site when using hosts.allow functionality -- eg. sendmail will > apparently go through all of the stages of accepting an incoming e-mail from > a denied host, right up to the 'MAIL FROM...' section of the SMTP transaction > where it will respond with a 500 permanent failure error code. [admittedly > this does have the benefit that the other side will then immediately give up > trying to send the message if it's playing by the RFC rules. (Most spam-bots > don't, of course.) Otherwise, you'ld get the remote side retrying the message > several times an hour over the next 5 days before it timed out and gave up. > > > Also, apparently in older ssh there was DenyHosts option, > > but no longer in the current version. > > Is there a replacement for DenyHOsts? > > Or is there a good reason for such option not to be used? > > I believe you can do something like this: > > match address 192.168.23.0/24,172.16.0.0/16 > ForceCommand /usr/sbin/nologin > > but this is not foolproof, as it is run via the users' login shell > and a sufficiently cunning person can arrange for all sorts of interesting > things to happen from their shell initialization files... Matthew, this makes sense many thanks anton -- Anton Shterenlikht Room 2.6, Queen's Building Mech Eng Dept Bristol University University Walk, Bristol BS8 1TR, UK Tel: +44 (0)117 331 5944 Fax: +44 (0)117 929 4423