CVE 2015-7713
OpenStack Compute (Nova) before 2014.2.4 (juno) and 2015.1.x before 2015.1.2 (kilo) do not properly apply security group changes, which allows remote attackers to bypass intended restriction by leveraging an instance that was running when the change was made.
See the 
CVE page on Mitre.org
for more details.
