From owner-freebsd-security@FreeBSD.ORG Wed Jan 29 14:31:16 2014 Return-Path: Delivered-To: freebsd-security@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [8.8.178.115]) (using TLSv1 with cipher ADH-AES256-SHA (256/256 bits)) (No client certificate requested) by hub.freebsd.org (Postfix) with ESMTPS id E01BE8C4 for ; Wed, 29 Jan 2014 14:31:16 +0000 (UTC) Received: from batman.home4u.ch (batman.home4u.ch [IPv6:2001:8a8:1005:1::2]) (using TLSv1 with cipher DHE-RSA-CAMELLIA256-SHA (256/256 bits)) (No client certificate requested) by mx1.freebsd.org (Postfix) with ESMTPS id 6F7801F5C for ; Wed, 29 Jan 2014 14:31:16 +0000 (UTC) X-Virus-Scanned: amavisd-new at home4u.ch Received: from flashback.wenks.ch (fabian@flashback.wenks.ch [IPv6:2001:8a8:1005:1::4]) (authenticated bits=0) by batman.home4u.ch (8.14.5/8.14.5) with ESMTP id s0TEVDbx051387 (version=TLSv1/SSLv3 cipher=DHE-RSA-CAMELLIA256-SHA bits=256 verify=NO) for ; Wed, 29 Jan 2014 15:31:13 +0100 (CET) (envelope-from fabian@wenks.ch) Message-ID: <52E910B0.4030606@wenks.ch> Date: Wed, 29 Jan 2014 15:31:12 +0100 From: Fabian Wenk User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.9; rv:24.0) Gecko/20100101 Thunderbird/24.2.0 MIME-Version: 1.0 To: freebsd-security@freebsd.org Subject: Re: portscans and blackhole References: <52DD08F7.1000306@hfbk-hamburg.de> In-Reply-To: <52DD08F7.1000306@hfbk-hamburg.de> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 8bit X-BeenThere: freebsd-security@freebsd.org X-Mailman-Version: 2.1.17 Precedence: list List-Id: "Security issues \[members-only posting\]" List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 29 Jan 2014 14:31:16 -0000 Hello On 20.01.14 12:31, sa9k063 wrote: > can someone please explain: > > one of my boxes gets portscanned often by some likely infected laptops. > While having set > > net.inet.tcp.blackhole=1 > > there are still messages like > > +Limiting closed port RST response from 348 to 200 packets/sec According to the blackhole(4) manpage (from a FreeBSD 9.1 system): ---8<------------------------------------------------------------ SYNOPSIS sysctl net.inet.tcp.blackhole[=[0 | 1 | 2]] sysctl net.inet.udp.blackhole[=[0 | 1]] Part of DESCRIPTION: Normal behaviour, when a TCP SYN segment is received on a port where there is no socket accepting connections, is for the system to return a RST segment, and drop the connection. The connecting system will see this as a “Connection refused”. By setting the TCP blackhole MIB to a numeric value of one, the incoming SYN segment is merely dropped, and no RST is sent, making the system appear as a blackhole. By setting the MIB value to two, any segment arriving on a closed port is dropped without returning a RST. This provides some degree of protection against stealth port scans. ---8<------------------------------------------------------------ So it is possible, that you are hit with something else then SYN packets and should probably set net.inet.tcp.blackhole=2, or even with UDP packets, then also set net.inet.udp.blackhole=1. What output does 'sysctl -a | grep blackhole' show? bye Fabian