In Folsom release, the security groups feature is provided by Nova not by Quantum. You can configure security group rules by using nova secgroup-add-rule or euca-authorize command to enable accesses to your VMs. The example below allows ping or ssh to your VMs.
$ nova secgroup-add-rule default icmp -1 -1 0.0.0.0/0 $ nova secgroup-add-rule default tcp 22 22 0.0.0.0/0
For more detail about Nova security groups, please see "Networking with nova-network" in OpenStack Compute Administration Manual.