
This is the Title of the Book, eMatter Edition
Copyright © 2007 O’Reilly & Associates, Inc. All rights reserved.
43
Chapter 3
CHAPTER 3
Hardening Linux and
Using iptables
There’s tremendous value in isolating your bastion (Internet-accessible) hosts in a
DMZ network, protected by a well-designed firewall and other external controls.
And just as a good DMZ is designed assuming that sooner or later, even firewall-pro-
tected hosts may be compromised, good bastion server design dictates that each host
should be hardened as though there were no firewall at all.
Obviously, the bastion-host services to which your firewall allows access must be
configured as securely as possible and kept up to date with security patches. But that
isn’t enough: you must also secure the bastion host’s operating-system configuration
and disable unnecessary services—in short, “bastionize” or “harden” it as much as
possible.
If you don’t do this, you won’t have a bastion server: you’ll simply have a server
behind a firewall—one that’s at the mercy of the firewall and the effectiveness of its
own applications’ security features. But if you do bastionize it, your server can
defend itself should some other host in the DMZ be compromised and used to attack
it. (As you can see, pessimism is an important element in risk management!)
Hardening a Linux system is not a trivial task: it’s as much work to bastionize Linux
as Solaris, Windows, ...