Ubuntu Security Notice 533-1 – Ludwig Nussel discovered that mount and umount did not properly drop privileges when using helper programs. Local attackers may be able to bypass security restrictions and gain root privileges using programs such as mount.nfs or mount.cifs.
You can download this advisory from the following link: https://packetstormsecurity.com/files/download/60325/USN-533-1.txt
Source: https://packetstormsecurity.com/files/60325/Ubuntu-Security-Notice-533-1.html