The XML libraries for Python 3.4, 3.3, 3.2, 3.1, 2.7, and 2.6, as used in OpenStack Keystone Essex and Folsom, Django, and possibly other products allow remote attackers to read arbitrary files via an XML external entity declaration in conjunction with an entity reference, aka an XML External Entity (XXE) attack.
https://bugs.launchpad.net/keystone/+bug/1100279
http://www.openwall.com/lists/oss-security/2013/02/19/4
http://www.openwall.com/lists/oss-security/2013/02/19/2
http://www.debian.org/security/2013/dsa-2634
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