Stack-based buffer overflow in sys/kern/vfs_mount.c in the kernel in FreeBSD 7.0 and 7.1, when vfs.usermount is enabled, allows local users to gain privileges via a crafted (1) mount or (2) nmount system call, related to copying of "user defined data" in "certain error conditions."

More... (http://nvd.nist.gov/nvd.cfm?cvename=CVE-2008-3531)