The auth_token middleware in the OpenStack Python client library for Keystone (aka python-keystoneclient) before 0.7.0 does not properly retrieve user tokens from memcache, which allows remote authenticated users to gain privileges in opportunistic circumstances via a large number of requests, related to an "interaction between eventlet and python-memcached."
https://bugs.launchpad.net/python-keystoneclient/+bug/1282865
http://www.openwall.com/lists/oss-security/2014/03/27/4