Increasing Security on Kerberos Servers

Follow these steps to increase security on Kerberos application servers and on KDC servers.

How to Enable Only Kerberized Applications

This procedure restricts network access to the server that is running telnet, ftp, rcp, rsh, and rlogin to use Kerberos authenticated transactions only.

1. Change the exec property for the telnet service.

   Add the -a user option to the exec property for telnet to restrict access to those users who can provide valid authentication information.

   # inetadm -m svc:/network/telnet:default exec="/usr/sbin/in.telnetd -a user"

2. (Optional) If not already configured, change the exec property for the telnet service.

   Add the -a option to the exec property for ftp to permit only Kerberos authenticated connections.

   # inetadm -m svc:/network/ftp:default exec="/usr/sbin/in.ftpd -a"

3. Disable other services.

   The in.rshd and in.rlogind daemons should be disabled.

   # svcadm disable network/shell
   # svcadm disable network/login:rlogin

How to Restrict Access to KDC Servers

Both master KDC servers and slave KDC servers have copies of the KDC database stored locally. Restricting access to these servers so that the databases are secure is important to the overall security of the Kerberos installation.

1. Disable remote services, as needed.

   To provide a secure KDC server, all nonessential network services should be disabled . Depending on your configuration, some of these services may already be disabled. Check the service status with the svcs command. In most circumstances, the only services that would need to run would be krb5kdc and krdb5_kprop if the KDC is a slave or only kadmin if the KDC is a master. In addition, any services that use loopback tli (ticlts, ticotsord, and ticots) can be left enabled.

   # svcadm disable network/comsat
   # svcadm disable network/dtspc/tcp
   # svcadm disable network/finger
   # svcadm disable network/login:rlogin
   # svcadm disable network/rexec
   # svcadm disable network/shell
   # svcadm disable network/talk
   # svcadm disable network/tname
   # svcadm disable network/uucp
   # svcadm disable network/rpc_100068_2-5/rpc_udp

2. Restrict access to the hardware that supports the KDC.

   To restrict physical access, make sure that the KDC server and its monitor are located in a secure facility. Users should not be able to access this server in any way.

3. Store KDC database backups on local disks or on the KDC slaves.

   Make tape backups of your KDC only if the tapes are stored securely. Follow the same practice for copies of keytab files. It would be best to store these files on a local file system that is not shared with other systems. The storage file system can be on either the master KDC server or any of the slave KDCs.