S 5.20 Use of the security mechanisms of rlogin, rsh and rcp

Initiation responsibility: IT Security Management, Administrators

Implementation responsibility: Administrators

With the rlogin programme and/or the associated daemon rlogind it is possible to log in on another computer through a network connection; in that case, however, only the password will be requested since the user name will be passed on directly. With the commands rsh or rcp and the rshd daemon, it is possible to execute commands on another computer. Both commands use trusted hosts which are defined either user-specifically in the home directory $HOME/.rhosts file or system-wide in the /etc/hosts.equiv file. Any computer entered in one of these files will be considered trusted so that it can log in (with rlogin) or execute a command (with rsh) without giving a password. Since it is very easy, especially from a PC, to impersonate any computer name, it must be ensured that the $HOME/.rhosts and /etc/hosts.equiv files are not existent or are unwriteable to the user. To achieve this, the home directories of the users should be regularly checked, or starting the daemons rlogind and rshd should be prevented (in this regard, cf. the /etc/inetd.conf file and safeguard S 5.16 ). If use of the /etc/hosts.equiv file cannot be avoided, it must be ensured that no ´+´ entry exists as that would result in any computer becoming a trusted one.