Best of the Newsgroups: why server should not be on net security firewall

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Date: Mon, 23 Dec 2002 18:05:08 -0500
From: Anthony Lawrence <tony@pcunix.com>
Subject: Re: ipfilter security
References: <d4e3407b.0212231247.22f5c291@posting.google.com> 

Fernando Ronci wrote:
> Hi,
> 
> Why do many "security" people (not here though) claim that the sole
> use of ipfilter as a firewall is not enough, and that the whole
> system's security can be compromised ?

I'm not sure people have said exactly that.

For example, what I have said more than once is that I don't think 
production servers should be directly attached to the net.  I think they 
should always be reached only through one or more other firewalls that 
are doing nothing BUT act as a filter for the internal machines.  That's 
not to say that the internal machines shouldn't also be configured 
securely (as though they were directly connected - in other words, 
non-essential services shut off, security patches reasonably current, 
packet filtering in place etc.).

There are several reasons I hold that opinion:

o More security is always better than less.  Important resources should 
have better protection.

o Internal servers are apt to lag behind in patches and OS updates 
simply because such things may affect critical apps running theron. 
Firewalls that do nothing but security won't be crippled by that need.

o Internal servers are apt to lag behind in patches and OS updates 
because financial people don't want to spend money on something that 
works.  It's easier (and often cheaper for various reasons) to keep a 
separate firewall up to date than an internal production server.  For example,
an OS update that would affect security might cost much more than 
upgrading a firewall for the same fix because the server may require 
costly application updates.

o People hate to take down internal servers to do updates because it 
affects real work.  Often you can live without the internet for a few 
hours but not without the production server, so updates get delayed.

o Internal servers are more subject to accidental security problems such 
as incorrect permissions.  This is often done (again) in the interests 
of making applications easier.

o Internal servers are quite apt to have dozens of accounts with weak 
passwords.  It's generally easier to enforce strong password policy for 
external access.  Such access can also be limited to only the accounts 
that reallly need it.  Joe has to login 2 or 3 times if he's coming in 
remotely, but he won't usually object to that as much as having a long 
internal password.  And if he does object, it's an easier battle to fight.

o Internal servers are (obviously) already open for access to inside 
people who can accidentally or on purpose open up more access by their 
actions.  It's often necessary or expedient to give relatively 
unsophisticated users some system level access for routine maintenance. 
  Such access is not necessary on a dedicated firewall.

o Internal servers may need to advertise services that are dangerous on 
the Internet.  Yes, you can and should filter those services but even 
better is not even have them ever get near the outside world in the 
first place.  If services are accidentally turned on, or local filter 
rules forgot to account for the outside world, it won't matter if the 
firewall is rigorously blocking everything that is not explicitly allowed.

I'm sure there is more others can add, but this should be enough.  In my 
opinion, it's just dumb to have an internal server with a public interface.






-- 
Tony Lawrence
Free  Linux Skills Test: http://aplawrence.com/skillstest.html

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