System Administration Guide: Network Services

Secure NFS System

The NFS environment is a powerful way and convenient way to share file systems on a network of different computer architectures and operating systems. However, the same features that make sharing file systems through NFS operation convenient also pose some security problems. Historically, most NFS implementations have used UNIX (or AUTH_SYS) authentication, but stronger authentication methods such as AUTH_DH have also been available. When using UNIX authentication, an NFS server authenticates a file request by authenticating the computer that makes the request, but not the user. Therefore, a client user can run su and impersonate the owner of a file. If DH authentication is used, the NFS server authenticates the user, making this sort of impersonation much harder.

With root access and knowledge of network programming, anyone can introduce arbitrary data into the network and extract any data from the network. The most dangerous attacks are those attacks that involve the introduction of data. An example is the impersonation of a user by generating the right packets or by recording “conversations” and replaying them later. These attacks affect data integrity. Attacks that involve passive eavesdropping, which is merely listening to network traffic without impersonating anybody, are not as dangerous, because data integrity is not compromised. Users can protect the privacy of sensitive information by encrypting data that is sent over the network.

A common approach to network security problems is to leave the solution to each application. A better approach is to implement a standard authentication system at a level that covers all applications.

The Solaris operating system includes an authentication system at the level of the remote procedure call (RPC), which is the mechanism on which the NFS operation is built. This system, known as Secure RPC, greatly improves the security of network environments and provides additional security to services such as the NFS system. When the NFS system uses the facilities that are provided by Secure RPC, it is known as a Secure NFS system.