The password hasher in contrib/auth/hashers.py in Django before 1.8.10 and 1.9.x before 1.9.3 allows remote attackers to enumerate users via a timing attack involving login requests.
https://www.djangoproject.com/weblog/2016/mar/01/security-releases/
https://github.com/django/django/commit/67b46ba7016da2d259c1ecc7d666d11f5e1cfaab
http://www.ubuntu.com/usn/USN-2915-3
http://www.ubuntu.com/usn/USN-2915-2
http://www.ubuntu.com/usn/USN-2915-1
http://www.securitytracker.com/id/1035152
http://www.securityfocus.com/bid/83878
http://www.oracle.com/technetwork/topics/security/bulletinapr2016-2952098.html
http://www.debian.org/security/2016/dsa-3544
http://rhn.redhat.com/errata/RHSA-2016-0506.html
http://rhn.redhat.com/errata/RHSA-2016-0505.html