Special Considerations With Firewalls
Next: The Role of
Up: Improving Network Security
Previous: Examples of Firewalls
Because the compromise of a firewall would be potentially disastrous
to subnet security, a number of special considerations need to be taken
with regard to firewall configuration and use.
The following list, adapted from [GS91], summarizes these items:
- limit firewall accounts to only those absolutely necessary, such
as for the administrator.
If practical, disable network logins.
- use authentication tokens to provide a much higher degree of security
than that provided by simple passwords.
Challenge-response and one-time password cards are easily integrated
with most popular operating systems.
- remove compilers, editors, and other program-development tools from
the firewall system(s) that could enable a cracker to install Trojan horse
software or backdoors.
- do not run any vulnerable protocols on the firewall such as tftp, NIS,
NFS, UUCP, or X.
- the finger protocol can leak valuable user information, consider
- on e-mail gateways, consider disabling the EXPN and VRFY commands,
which can be used by crackers to probe for user addresses.
- do not permit the firewall systems to ``trust'' other systems; the
firewall should not be equivalent to any other system.
- disable any feature of the firewall system that is not needed,
including other network access, user shells, applications, and so forth.
- turn on full-logging at the firewall and read the logs routinely.
Fri Oct 7 16:17:21 EDT 1994