All port groups on standard switches must be configured to reject guest Media Access Control (MAC) address changes.

If the virtual machine (VM) 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, which will affect applications that require this functionality. This will also affect how a layer 2 bridge will operate and will affect applications that require a specific MAC address for licensing. "Reject MAC Changes" can be set at the vSwitch and/or the Portgroup level. Switch-level settings can be overridden at the Portgroup level.

Note: This control addresses ESXi standard switches. Distributed switches are addressed in the vCenter STIG. If there is no standard switch on the ESXi host, this is not applicable.

From the vSphere Client, go to Hosts and Clusters.

Select the ESXi Host >> Configure >> Networking >> Virtual Switches.

On each standard switch, click the "..." button next to each port group. Click View Settings >> Policies tab.

Verify "MAC Address Changes" is set to "Reject".

or

From a PowerCLI command prompt while connected to the ESXi host, run the following commands:

Get-VirtualSwitch -Standard | Get-SecurityPolicy Get-VirtualPortGroup -Standard | Get-SecurityPolicy

If the "MAC Address Changes" policy is set to "Accept" (or "true", via PowerCLI), this is a finding.

From the vSphere Client, go to Hosts and Clusters.

Select the ESXi Host >> Configure >> Networking >> Virtual Switches.

On each standard switch, click the "..." button next to each port group. Click Edit Settings >> Security tab.

Set "MAC Address Changes" to "Reject".

or

From a PowerCLI command prompt while connected to the ESXi host, run the following commands:

Get-VirtualSwitch -Standard | Get-SecurityPolicy | Set-SecurityPolicy -MacChanges $false Get-VirtualPortGroup -Standard | Get-SecurityPolicy | Set-SecurityPolicy -MacChangesInherited $true