CVE-2017-7543
A race-condition flaw was discovered in openstack-neutron before 7.2.0-12.1, 8.x before 8.3.0-11.1, 9.x before 9.3.1-2.1, and 10.x before 10.0.2-1.1, where, following a minor overcloud update, neutron security groups were disabled. Specifically, the following were reset to 0: net.bridge.bridge-nf-call-ip6tables and net.bridge.bridge-nf-call-iptables. The race was only triggered by an update, at which point an attacker could access exposed tenant VMs and network resources.
Source: CVE-2017-7543