From owner-freebsd-hackers Tue Feb 18 5:31:15 2003 Delivered-To: freebsd-hackers@freebsd.org Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125]) by hub.freebsd.org (Postfix) with ESMTP id D8B3437B401 for ; Tue, 18 Feb 2003 05:31:13 -0800 (PST) Received: from smtp.mailbox.co.uk (smtp.mailbox.co.uk [195.82.125.32]) by mx1.FreeBSD.org (Postfix) with ESMTP id C69CE43FA3 for ; Tue, 18 Feb 2003 05:31:12 -0800 (PST) (envelope-from wayne@penguinpowered.org.uk) Received: from [212.18.244.168] (helo=marvin.penguinpowered.org.uk) by smtp.mailbox.co.uk with esmtp (Exim 3.36 #1) id 18l7q3-0000Ad-00 for freebsd-hackers@freebsd.org; Tue, 18 Feb 2003 13:31:11 +0000 Received: from waynep by marvin.penguinpowered.org.uk with local (Exim 3.33 #1) id 18l7zk-000OKc-00 for freebsd-hackers@freebsd.org; Tue, 18 Feb 2003 13:41:12 +0000 Date: Tue, 18 Feb 2003 13:41:12 +0000 From: Ian Watkinson To: freebsd-hackers@freebsd.org Subject: DHCP Client DoS Message-ID: <20030218134112.GA93504@marvin.penguinpowered.org.uk> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.4i X-System: FreeBSD i386 with kernel 4.7-RC Sender: owner-freebsd-hackers@FreeBSD.ORG Precedence: bulk List-ID: List-Archive: (Web Archive) List-Help: (List Instructions) List-Subscribe: List-Unsubscribe: X-Loop: FreeBSD.ORG Hi all, We've recently found a problem with dhclient that can DoS a DHCP server. If you have schg flags set on /etc/resolv.conf to stop dhcp overwriting your existing nameservers, the problem occurs. Basically, the client just keeps rejecting the IP details it has received from the server and requesting another. The server marks the record as used, and moves onto the next one. Over the course of a couple of minutes, you can pretty much mark an entire class C as in use. If you remove the schg flag from resolv.conf, this problem does not happen. This has been tested from a FreeBSD 5 client against a Windows NT server and a FreeBSD 4.7 server with the same results. -- Ian Watkinson To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message