Linux Server Security, Second Edition

This is the Title of the Book, eMatter Edition

Copyright © 2007 O’Reilly & Associates, Inc. All rights reserved.

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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, ...