Date: Wed, 28 Jul 2010 15:31:45 -0400 From: Jon Radel <jon@radel.com> To: freebsd-pf@freebsd.org Subject: Re: For better security: always "block all" or "block in all" is enough? Message-ID: <4C5085A1.6070905@radel.com> In-Reply-To: <20290C577F743240B5256C89EFA753810C46894B92@HIKAWSEX01.ad.harman.com> References: <20290C577F743240B5256C89EFA753810C46894B92@HIKAWSEX01.ad.harman.com>
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This is a cryptographically signed message in MIME format. --------------ms000908020603000906060608 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: quoted-printable On 7/28/10 2:55 PM, Spenst, Aleksej wrote: > Hi All, > > I have to provide for my system better security and I guess it would be= better to start pf.conf with the "block all" rule opening afterwards onl= y those incoming and outcoming ports that are supposed to be used by the = system on external interfaces. However, it would be easier for me to writ= e all pf rules if I start pf.conf with "block in all", i.e. if I block on= ly traffic coming in from the outside and open all ports for outgoing tra= ffic. > > - Incoming ports: only udp/68 (for dhcp client) and http/80 (for http s= erver) always open; > - Outgoing ports: all ports always opened. All traffic going outside fr= om the system has "keep state"; > > What disadvantages does it have in term of security in comparison with = "block all"? In other words, how bad it is to have all outgoing ports alw= ays opened and whether someone can use this to hack the sysem? > > Thanks a lot for any tips!! > Aleksej. > > =20 The only real answer is: It depends. :-) One example of outbound blocking that some find useful: Block all=20 outbound traffic to port 25 that comes from any machine other than=20 authorized e-mail servers. On one network I deal in, this makes sense,=20 as the various Windows workstations have no business sending mail to=20 anything other than the internal mail servers, and if they try there's a = good chance it's a trojan of some sort doing the sending. Obviously,=20 there are other networks where this would make no sense. In a general sort of way, allowing outbound traffic doesn't expose you=20 to attacks, but it makes your machine more valuable to an attacker who=20 does succeed. For example, if you allow outbound ssh and telnet, etc.,=20 etc., it makes it easier to use your machine to stage attacks on other=20 machines. On the other hand, if the firewall is on the server in=20 question, rather than being another piece of equipment, anybody who has=20 root can rearrange your firewall for you.... --=20 --Jon Radel jon@radel.com --------------ms000908020603000906060608--
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