OpenStack Compute (nova) 2015.1 through 2015.1.1, 2014.2.3, and earlier does not stop the migration process when the instance is deleted, which allows remote authenticated users to cause a denial of service (disk, network, and other resource consumption) by resizing and then deleting an instance.
https://security.openstack.org/ossa/OSSA-2015-015.html
https://launchpad.net/bugs/1387543
http://www.securityfocus.com/bid/75372