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This bulletin was written by Vigil@nce : http://vigilance.fr/

SYNTHESIS OF THE VULNERABILITY

A local attacker can mount a malicious NFS filesystem, in order to
generate a buffer overflow, and to obtain root privileges.

– Severity: 2/4
– Creation date: 27/05/2010

DESCRIPTION OF THE VULNERABILITY

The vfs.usermount sysctl indicates if local users are allowed to
mount a file system. By default, this action is forbidden.

The NFS client is automatically called when vfs.usermount is set
to one, and when the user uses a NFS server.

However, the nfs_mount() function of the sys/nfsclient/nfs_vfsops.c
file does not check the size of the File Handle indicated by the
NFS server. An overflow thus occurs.

A local attacker can therefore mount a malicious NFS filesystem,
in order to generate a buffer overflow, and to obtain root
privileges.

ACCESS TO THE COMPLETE VIGIL@NCE BULLETIN

http://vigilance.fr/vulnerability/FreeBSD-privilege-elevation-via-the-NFS-client-9672