The ESXi host must configure virtual switch security policies to reject Media Access Control (MAC) address changes.

Overview

Finding ID	Version	Rule ID	IA Controls	Severity
V-258772	ESXI-80-000217	SV-258772r959010_rule		High

Description
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.

Description

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.

STIG	Date
VMware vSphere 8.0 ESXi Security Technical Implementation Guide	2024-07-11

Details

Check Text ( C-62512r933375_chk )
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 and select "Edit Settings". Click the "Security" tab. Verify that "MAC Address Changes" is set to "Reject" and that "Override" is not checked. or From a PowerCLI command prompt while connected to the ESXi host, run the following commands: Get-VirtualSwitch \| Get-SecurityPolicy Get-VirtualPortGroup \| Get-SecurityPolicy \| Select-Object * If the "MAC Address Changes" policy is set to "Accept" (or "true", via PowerCLI) or the security policy inherited from the virtual switch is overridden, this is a finding.

Check Text ( C-62512r933375_chk )

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 and select "Edit Settings".

Click the "Security" tab. Verify that "MAC Address Changes" is set to "Reject" and that "Override" is not checked.

or

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

Get-VirtualSwitch | Get-SecurityPolicy
Get-VirtualPortGroup | Get-SecurityPolicy | Select-Object *

If the "MAC Address Changes" policy is set to "Accept" (or "true", via PowerCLI) or the security policy inherited from the virtual switch is overridden, this is a finding.

Fix Text (F-62421r933376_fix)
From the vSphere Client, go to Hosts and Clusters. Select the ESXi Host >> Configure >> Networking >> Virtual Switches. On each standard switch, click "Edit" and select Security. Set "MAC Address Changes" to "Reject". Click "OK". For each port group, click the '...' button and select "Edit Settings" then Security. Set "MAC Address Changes" to "Reject" and uncheck the "Override" box. Click "OK". or From a PowerCLI command prompt while connected to the ESXi host, run the following commands: Get-VirtualSwitch \| Get-SecurityPolicy \| Set-SecurityPolicy -MacChanges $false Get-VirtualPortGroup \| Get-SecurityPolicy \| Set-SecurityPolicy -MacChangesInherited $true

Fix Text (F-62421r933376_fix)

From the vSphere Client, go to Hosts and Clusters.

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

On each standard switch, click "Edit" and select Security.

Set "MAC Address Changes" to "Reject". Click "OK".

For each port group, click the '...' button and select "Edit Settings" then Security.

Set "MAC Address Changes" to "Reject" and uncheck the "Override" box. Click "OK".

or

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

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