sys/nfsclient/nfs_vfsops.c in the NFS client in the kernel in FreeBSD 7.2 through 8.1-PRERELEASE, when vfs.usermount is enabled, does not validate the length of a certain fhsize parameter, which allows local users to gain privileges via a crafted mount request.
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.