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: Hardening Linux and Using iptables

HTML, ASCII, L

A

T

E

X, and, of course, a proprietary Nessus Report format, NBE

(which you should use for reports you wish to view again within Nessus).

Read this report carefully. Be sure to expand all + boxes and fix the things Nessus

turns up. Nessus can find problems and can even suggest solutions, but it won’t fix

things for you. Also, Nessus won’t necessarily find everything wrong with your sys-

tem.

Returning to our woofgang example (see Figure 3-8), Nessus has determined that

woofgang may be running a vulnerable version of OpenSSH! Even after all the things

we’ve done so far to harden this host, we may still have a major vulnerability to take

care of. I say “may” because, as the Nessus report notes, Nessus made this inference

based on sshd’s greeting banner, not by attempting to exploit the vulnerabilities of

this version of SSH. Because some distributions routinely patch software packages

without incrementing their version numbers, sshd on woofgang may or may not be

vulnerable. It’s up to me, at this point, to make sure that woofgang is indeed fully up

to date with security patches before putting this system into production.

Understanding and Using Available Security Features

This corollary to the Principle of Least Privilege is