From owner-freebsd-security@freebsd.org Sat Jul 21 11:03:47 2018 Return-Path: Delivered-To: freebsd-security@mailman.ysv.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2610:1c1:1:606c::19:1]) by mailman.ysv.freebsd.org (Postfix) with ESMTP id 89F1F1046D19 for ; Sat, 21 Jul 2018 11:03:47 +0000 (UTC) (envelope-from freebsd-list@nuos.org) Received: from cargobay.net (cargobay.net [23.111.168.34]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by mx1.freebsd.org (Postfix) with ESMTPS id 2DB54860F0 for ; Sat, 21 Jul 2018 11:03:46 +0000 (UTC) (envelope-from freebsd-list@nuos.org) Received: from [192.168.1.4] (unknown [67.8.153.7]) by jack.ccsys.com (Postfix) with ESMTPSA id E6B402B72 for ; Sat, 21 Jul 2018 11:03:38 +0000 (UTC) From: Chad Jacob Milios Mime-Version: 1.0 (Mac OS X Mail 11.5 \(3445.9.1\)) Subject: Re: Possible break-in attempt? Date: Sat, 21 Jul 2018 07:03:38 -0400 References: <594ba84b-0691-8471-4bd4-076d0ae3da98@gjunka.com> <368EABCF-A10A-49E9-9473-7753F6BEAA50@patpro.net> <8EDDBDB2-77F5-4CF5-8744-41BEA187C08A@FreeBSD.org> <201807201905.w6KJ59hn079229@donotpassgo.dyslexicfish.net> To: freebsd-security@freebsd.org In-Reply-To: <201807201905.w6KJ59hn079229@donotpassgo.dyslexicfish.net> Message-Id: <2E502F45-E6F6-44D7-AE9E-9B8B08C1CEBE@nuos.org> X-Mailer: Apple Mail (2.3445.9.1) Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable X-Content-Filtered-By: Mailman/MimeDel 2.1.27 X-BeenThere: freebsd-security@freebsd.org X-Mailman-Version: 2.1.27 Precedence: list List-Id: "Security issues \[members-only posting\]" List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sat, 21 Jul 2018 11:03:47 -0000 > On Jul 20, 2018, at 3:05 PM, Jamie Landeg-Jones = wrote: >=20 > Dimitry Andric wrote: >=20 >> For each incoming IP address, sshd does a reverse lookup, and if that >> results in a hostname, it does another lookup of that hostname, to = see >> if *that* result matches the original incoming IP address. If it = does >> not, you get this scary warning in syslog about a "possible break-in >> attempt!". >>=20 >> In my opinion, this is fairly misleading, since almost always the = actual >> cause is badly configured DNS, a very common occurrence. In = addition, >> matching forward and reverse DNS records is no guarantee at all that = the >> incoming IP address is in any way trustworthy. >=20 > I'm not sure which version this made it into, but they actually = removed this > over 2 years ago. It's not in the openssh that ships with FreeBSD = 11.2: >=20 > | commit e690fe85750e93fca1fb7c7c8587d4130a4f7aba > | Author: dtucker@openbsd.org > | Date: Wed Jun 15 00:40:40 2016 +0000 > | > | upstream commit > | > | Remove "POSSIBLE BREAK-IN ATTEMPT!" from log message > | about forward and reverse DNS not matching. We haven't = supported IP-based > | auth methods for a very long time so it's now misleading. part = of bz#2585, > | ok markus@ > | > | Upstream-ID: 5565ef0ee0599b27f0bd1d3bb1f8a323d8274e29 >=20 > cheers, Jamie adding: UseDNS no has the added benefit of avoiding a grueling delay when YOU are the one = behind an IP address with a misconfigured reverse DNS mapping (which is = horribly common on consumer networks). It goes into /etc/ssh/sshd_config = and has been among my initial configuration to every FreeBSD box i=E2=80=99= ve stood up for a decade. openssh-portable (in ports, produced by the paranoid fellows at OpenBSD) = has actually switched to adopt this, UseDNS no, as their default = configuration for, i think its been a couple years now. This is in = addition to dropping the message from their log output if UseDNS yes. There is no point to this foolishly alarming message. Be mindful of the = OTHER ways you must surely have in place to keep your sshd hard against = attack. -CJ=