OpenStack Compute (Nova) Grizzly 2013.1.4, Havana 2013.2.1, and earlier uses world-writable and world-readable permissions for the temporary directory used to store live snapshots, which allows local users to read and modify live snapshots.
The libvirt driver in OpenStack Compute (Nova) before 2013.2.2 and icehouse before icehouse-2 allows remote authenticated users to cause a denial of service (disk consumption) by creating and deleting instances with unique ostype settings, which triggers the creation of a new ephemeral disk backing file.