The nfsrvd_readdir function in sys/fs/nfsserver/nfs_nfsdport.c in the new NFS server in FreeBSD 8.0 through 9.1-RELEASE-p3 does not verify that a READDIR request is for a directory node, which allows remote attackers to cause a denial of service (memory corruption) or possibly execute arbitrary code by specifying a plain file instead of a directory.
Improper Input Validation The product receives input or data, but it does
not validate or incorrectly validates that the input has the
properties that are required to process the data safely and
correctly.