The ec2tokens API in OpenStack Identity (Keystone) before Havana 2013.2.1 and Icehouse before icehouse-2 does not return a trust-scoped token when one is received, which allows remote trust users to gain privileges by generating EC2 credentials from a trust-scoped token and using them in an ec2tokens API request.
https://exchange.xforce.ibmcloud.com/vulnerabilities/89657
http://www.ubuntu.com/usn/USN-2061-1
http://www.securityfocus.com/bid/64253
http://www.openwall.com/lists/oss-security/2013/12/11/7
http://secunia.com/advisories/56154