utils/mount.ecryptfs_private.c in ecryptfs-utils before 90 does not properly check mountpoint permissions, which allows local users to effectively replace any directory with a new filesystem, and consequently gain privileges, via a mount system call.
https://launchpad.net/ecryptfs/+download
https://bugzilla.redhat.com/show_bug.cgi?id=729465
http://www.ubuntu.com/usn/USN-1188-1
http://lists.opensuse.org/opensuse-security-announce/2011-08/msg00009.html