The XML libraries for Python 3.4, 3.3, 3.2, 3.1, 2.7, and 2.6, as used in OpenStack Keystone Essex, Folsom, and Grizzly; Compute (Nova) Essex and Folsom; Cinder Folsom; Django; and possibly other products allow remote attackers to cause a denial of service (resource consumption and crash) via an XML Entity Expansion (XEE) attack.
http://www.openwall.com/lists/oss-security/2013/02/19/4
http://www.openwall.com/lists/oss-security/2013/02/19/2
http://ubuntu.com/usn/usn-1757-1
http://rhn.redhat.com/errata/RHSA-2013-0670.html
http://rhn.redhat.com/errata/RHSA-2013-0658.html
http://rhn.redhat.com/errata/RHSA-2013-0657.html
http://lists.openstack.org/pipermail/openstack-announce/2013-February/000078.html
http://bugs.python.org/issue17239
http://blog.python.org/2013/02/announcing-defusedxml-fixes-for-xml.html