NFS 3 and the specter of the spoof attack

Ghost on the Loose

© Snowshill, Fotolia

© Snowshill, Fotolia

Article from Issue 99/2009
Author(s):

Host-based authentication is easy to configure, but it doesn't do much to stop uninvited guests.

The CIO of a famous credit union was fairly sure he had thought of everything: state-of-the-art antivirus tools, separate zones for desktops and servers, firewalls at strategic points, and regular operating system updates. He also favored "stable versions" of operating systems, applications, and protocols for added assurance.

Unfortunately, this CIO decided to take a short cut in setting up the file server: NFS version 3 [1] with the legacy "host-based access control" and no special hardening. Although NFS 4 has been around for several years, many networks continue to use NFS 3 because it is simpler and it is already up and running.

Ease of use is certainly an important consideration; however, in the case of NFS, this simplicity sometimes comes with a cost. The host-based scheme used with NFS 3 has several significant problems. Also, NFS 3 transmits unencrypted data blocks (see Figure 1), it only performs rudimentary authentication, and its authorization mechanisms are easily avoided (see the "NFS Security Functions" box).

[...]

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