OpenStack Compute (Nova) Grizzly, Folsom (2012.2), and Essex (2012.1) allows remote authenticated users to gain access to a VM in opportunistic circumstances by using the VNC token for a deleted VM that was bound to the same VNC port.
https://review.openstack.org/#/c/22872/
https://review.openstack.org/#/c/22758
https://review.openstack.org/#/c/22086/
https://bugs.launchpad.net/nova/+bug/1125378
http://www.ubuntu.com/usn/USN-1771-1
http://www.openwall.com/lists/oss-security/2013/02/26/7
http://secunia.com/advisories/52728