NET-NAC-031

Information

The switch must only allow a maximum of one registered MAC address per access port.

Limiting the number of registered MAC addresses on a switch access port can help prevent a CAM table overflow attack. This type of attack lets an attacker exploit the hardware and memory limitations of a switch. If there are enough entries stored in a CAM table before the expiration of other entries, no new entries can be accepted into the CAM table. An attacker will able to flood the switch with mostly invalid MAC addresses until the CAM table's resources have been depleted. When there are no more resources, the switch has no choice but to flood all ports within the VLAN with all incoming traffic. This happens because the switch cannot find the switch port number for a corresponding MAC address within the CAM table, allowing the switch to become a hub and traffic to be monitored.

NOTE: This check is derived from the L3 switch guidance, if the scan target is a router the check can be ignored.
NOTE: Nessus has not performed this check. Please review the benchmark to ensure target compliance.

Solution

Configuring port-security on the Cisco switch access port interface will automatically set the maximum number of registered MAC addresses to one. The value will not show up in the configuration of the switch itself. You must run the command 'Switch# show port-security interface' where interface is the specific switchport of interest.

See Also

https://iasecontent.disa.mil/stigs/zip/U_Network_Perimeter_Router_L3_Switch_V8R31_STIG.zip

Item Details

References: CAT|II, Rule-ID|SV-49133r1_rule, STIG-ID|NET-NAC-031, Vuln-ID|V-18566

Plugin: Cisco

Control ID: dff98c4142c659a20007d4e9ccf40609b521a9c33dcc30347161e3b4ee5da93b