From owner-freebsd-security@FreeBSD.ORG Sun Aug 20 00:34:26 2006 Return-Path: X-Original-To: freebsd-security@freebsd.org Delivered-To: freebsd-security@freebsd.org Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125]) by hub.freebsd.org (Postfix) with ESMTP id 283AE16A4DD; Sun, 20 Aug 2006 00:34:26 +0000 (UTC) (envelope-from rip@overflow.no) Received: from mail.mailwhiz.net (mail.mailwhiz.net [24.244.141.168]) by mx1.FreeBSD.org (Postfix) with ESMTP id D3D7343D55; Sun, 20 Aug 2006 00:34:25 +0000 (GMT) (envelope-from rip@overflow.no) Message-ID: <44E7AE0F.2000103@overflow.no> Date: Sat, 19 Aug 2006 20:34:23 -0400 From: Chris User-Agent: Thunderbird 1.5.0.5 (X11/20060728) MIME-Version: 1.0 To: Daniel Gerzo References: <44E76B21.8000409@thedarkside.nl> <47517034.20060819233730@rulez.sk> In-Reply-To: <47517034.20060819233730@rulez.sk> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Cc: freebsd-security@freebsd.org, Pieter de Boer Subject: Re: SSH scans vs connection ratelimiting X-BeenThere: freebsd-security@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: "Security issues \[members-only posting\]" List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sun, 20 Aug 2006 00:34:26 -0000 I'm maintaining a patch for OpenSSH portable that allows configurable blocking(firewalling, ipfw,ipf,iptables) of such bruteforce attempts. I will post it if anyone is interested in it. Daniel Gerzo wrote: > Hello Pieter, > > Saturday, August 19, 2006, 9:48:49 PM, you wrote: > > >> Gang, >> > > >> For months now, we're all seeing repeated bruteforce attempts on SSH. >> I've configured my pf install to ratelimit TCP connections to port 22 >> and to automatically add IP-addresses that connect too fast to a table >> that's filtered: >> > > >> table { } >> > > >> block quick from to any >> > > >> pass in quick on $ext_if inet proto tcp from any to ($ext_if) port 22 >> modulate state (source-track rule max-src-nodes 8 max-src-conn 8 >> max-src-conn-rate 3/60 overload flush global) >> > > > >> This works as expected, IP-addresses are added to the 'lamers'-table >> every once in a while. >> > > >> However, there apparently are SSH bruteforcers that simply use one >> connection to perform a brute-force attack: >> > > >> Aug 18 00:00:01 aberdeen sshd[87989]: Invalid user serwis from 83.19.113.122 >> Aug 18 00:00:03 aberdeen sshd[88010]: Invalid user serwis from 83.19.113.122 >> Aug 18 00:00:05 aberdeen sshd[88012]: Invalid user serwis from 83.19.113.122 >> Aug 18 00:00:10 aberdeen sshd[88014]: Invalid user serwis from 83.19.113.122 >> Aug 18 00:00:13 aberdeen sshd[88019]: Invalid user serwis from 83.19.113.122 >> Aug 18 00:00:14 aberdeen sshd[88021]: Invalid user serwis from 83.19.113.122 >> > > > >> My theory was/is that this particular scanner simply multiplexes >> multiple authentication attempts over a single connection. I 'used the >> source luke' of OpenSSH to find support for this theory, but found the >> source a bit too wealthy for my brain to find such support. >> > > >> So, my question is: Does anyone know how this particular attack works >> and if there's a way to stop this? If my theory is sound and OpenSSH >> does not have provisions to limit the authentication requests per TCP >> session, I'd find that an inadequacy in OpenSSH, but I'm probably >> missing something here :) >> > > try http://legonet.org/~griffin/openbsd/block_ssh_bruteforce.html > or my pet project http://danger.rulez.sk/projects/bruteforceblocker/ > > >> Regards, >> Pieter >> > >