When using the Linux bridge ml2 driver, non-privileged tenants are able to create and attach ports without specifying an IP address, bypassing IP address validation. A potential denial of service could occur if an IP address, conflicting with existing guests or routers, is then assigned from outside of the allowed allocation pool. Versions of openstack-neutron before 13.0.0.0b2, 12.0.3 and 11.0.5 are vulnerable.