The Fernet Token Provider in OpenStack Identity (Keystone) 9.0.x before 9.0.1 (mitaka) allows remote authenticated users to prevent revocation of a chain of tokens and bypass intended access restrictions by rescoping a token.
https://security.openstack.org/ossa/OSSA-2016-008.html
https://review.openstack.org/#/c/311886/
https://bugs.launchpad.net/keystone/+bug/1577558
http://www.securityfocus.com/bid/90728