Nova 2011.3 and Essex, when using the OpenStack API, allows remote authenticated users to bypass access restrictions for tenants of other users via an OSAPI request with a modified project_id URI parameter.
https://lists.launchpad.net/openstack/msg06648.html
https://github.com/openstack/nova/commit/3d4ffb64f1e18117240c26809788528979e3bd15#diff-0
https://exchange.xforce.ibmcloud.com/vulnerabilities/72296
http://www.ubuntu.com/usn/USN-1326-1