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5.3. Securing NIS
NIS stands for Network Information Service. It is an RPC service, called
ypserv, which is used in conjunction with
portmapand other related services to distribute maps of usernames, passwords, and other sensitive information to any computer claiming to be within its domain.
An NIS server is comprised of several applications. They include the following:
/usr/sbin/rpc.yppasswdd— Also called the
yppasswddservice, this daemon allows users to change their NIS passwords.
/usr/sbin/rpc.ypxfrd— Also called the
ypxfrdservice, this daemon is responsible for NIS map transfers over the network.
/usr/sbin/yppush— This application propagates changed NIS databases to multiple NIS servers.
/usr/sbin/ypserv— This is the NIS server daemon.
NIS is rather insecure by todays standards. It has no host authentication mechanisms and passes all of its information over the network unencrypted, including password hashes. As a result, extreme care must be taken to set up a network that uses NIS. Further complicating the situation, the default configuration of NIS is inherently insecure.
It is recommended that anyone planning to implement an NIS server first secure the
portmapservice as outlined in Section 5.2, “Securing Portmap”, then address the following issues, such as network planning.
5.3.1. Carefully Plan the Network
Because NIS passes sensitive information unencrypted over the network, it is important the service be run behind a firewall and on a segmented and secure network. Any time NIS information is passed over an insecure network, it risks being intercepted. Careful network design in these regards can help prevent severe security breaches.