Information
Ensure that the MAC Address Changes policy is set to reject.
If the virtual machine operating system changes the MAC address, it can send frames with an impersonated source MAC address at any time. This allows it to stage malicious attacks on the devices in a network by impersonating a network adaptor authorized by the receiving network. This will prevent VMs from changing their effective MAC address. It will affect applications that require this functionality. An example of an application like this is Microsoft Clustering, which requires systems to effectively share a MAC address. This will also affect how a layer 2 bridge will operate. This will also affect applications that require a specific MAC address for licensing. An exception should be made for the dvPortgroups that these applications are connected to.
http://pubs.vmware.com/vsphere-60/topic/com.vmware.vsphere.security.doc/GUID-C590B7D3-4E28-4F2B-8A59-4CDB9C6F2DAA.html
NOTE: Nessus has not performed this check. Please review the benchmark to ensure target compliance.
Solution
From vSphere web client, for each portgroup within each distributed switch go to "Manage" -> "Settings" -> "Policies" and click "Edit". Go to "Security" and set the "MAC address changes" policy to "Reject".