Ubuntu Security Notice USN-184-1 – David Watson discovered that umount -r removed some restrictive mount options like the nosuid flag. If /etc/fstab contains user-mountable removable devices which specify the nosuid flag (which is common practice for such devices), a local attacker could exploit this to execute arbitrary programs with root privileges by calling umount -r on a removable device.
You can download this advisory from the following link: https://packetstormsecurity.com/files/download/40172/USN-184-1.txt
Source: https://packetstormsecurity.com/files/40172/Ubuntu-Security-Notice-184-1.html