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Printable Version: RFC2196.PDF
RFC 2196 Site Security Handbook September 1997
(2) Changing default passwords - Many operating systems and
application programs are installed with default accounts and
passwords. These must be changed immediately to something that
cannot be guessed or cracked.
(3) Restricting access to the password file - In particular, a site
wants to protect the encrypted password portion of the file so
that would-be intruders don't have them available for cracking.
One effective technique is to use shadow passwords where the
password field of the standard file contains a dummy or false
password. The file containing the legitimate passwords are
protected elsewhere on the system.
(4) Password aging - When and how to expire passwords is still a
subject of controversy among the security community. It is
generally accepted that a password should not be maintained once
an account is no longer in use, but it is hotly debated whether
a user should be forced to change a good password that's in
active use. The arguments for changing passwords relate to the
prevention of the continued use of penetrated accounts.
However, the opposition claims that frequent password changes
lead to users writing down their passwords in visible areas
(such as pasting them to a terminal), or to users selecting very
simple passwords that are easy to guess. It should also be
stated that an intruder will probably use a captured or guessed
password sooner rather than later, in which case password aging
provides little if any protection.
While there is no definitive answer to this dilemma, a password
policy should directly address the issue and provide guidelines
for how often a user should change the password. Certainly, an
annual change in their password is usually not difficult for
most users, and you should consider requiring it. It is
recommended that passwords be changed at least whenever a
privileged account is compromised, there is a critical change in
personnel (especially if it is an administrator!), or when an
account has been compromised. In addition, if a privileged
account password is compromised, all passwords on the system
should be changed.
(5) Password/account blocking - Some sites find it useful to disable
accounts after a predefined number of failed attempts to
authenticate. If your site decides to employ this mechanism, it
is recommended that the mechanism not "advertise" itself. After
Fraser, Ed. Informational [Page 27]