48.2.3. Securing NIS
The Network Information Service (NIS) is an RPC service, called
ypserv,--> which is used in conjunction with portmap and 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 theyppasswddservice, this daemon allows users to change their NIS passwords./usr/sbin/rpc.ypxfrd— Also called theypxfrdservice, 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 somewhat insecure by today's standards. It has no host authentication mechanisms and transmits all of its information over the network unencrypted, including password hashes. As a result, extreme care must be taken when setting up a network that uses NIS. This is further complicated by the fact that the default configuration of NIS is inherently insecure.
It is recommended that anyone planning to implement an NIS server first secure the
portmap service as outlined in Section 48.2.2, “Securing Portmap”, then address the following issues, such as network planning.
48.2.3.1. Carefully Plan the Network
Because NIS transmits sensitive information unencrypted over the network, it is important the service be run behind a firewall and on a segmented and secure network. Whenever NIS information is transmitted over an insecure network, it risks being intercepted. Careful network design can help prevent severe security breaches.
