Host systems are difficult and time consuming to manage securely. To ease management demands and to enhance local area networking, some sites use services such as Network Information Services (NIS) and Network File System (NFS). These services can greatly reduce the amount of redundant management by permitting certain databases such as the password files to be managed in a distributed manner and by permitting systems to share files and data. Ironically, these services are inherently insecure and can be exploited to gain access by knowledgeable intruders. If a central server system is compromised, then the other systems trusting the central system could be compromised rather easily.
Some services such as rlogin allow for hosts to ``trust'' each other for the purposes of user convenience and enhanced sharing of systems and devices. If a system is penetrated or spoofed, and that system is trusted by other systems, it is simple for the intruder to then gain access to the other systems. As an example, a user with an account on more than one system can eliminate the need to enter a password at every system by configuring the accounts to trust connections from the user's primary system. When the user uses the rlogin command to connect to a host, the destination system will not ask for a password or account name, and the user's connection will be accepted. While this has a positive aspect in that the user's password does not get transmitted and could not be monitored and captured, it has a negative aspect in that if the user's primary account were to be penetrated, the intruder could simply use rlogin to penetrate the accounts on the other systems. For this reason, use of mutually-trusting hosts is discouraged [Bel89], [Ches94].