ESXi: esxi-8.network-reject-forged-transmit-standardswitch

Information

All standard switches and their port groups must be configured to reject forged transmits. If the MAC address of a virtual machine operating system changes, it allows the operating system to send frames with an impersonated source MAC address, potentially enabling malicious attacks on devices within a network by impersonating an authorized network adapter. When the "Forged transmits" option is set to "Accept," ESXi does not compare the source and effective MAC addresses. To protect against MAC impersonation, you can set the "Forged transmits" option to "Reject." In this case, the host compares the source MAC address being transmitted by the guest operating system with the effective MAC address for its virtual machine adapter to check for a match. If the addresses do not match, the ESXi host drops the packet.

Solution

Get-VMHost -Name $ESXi | Get-VirtualSwitch -Standard | Get-SecurityPolicy | Set-SecurityPolicy -ForgedTransmits $false
Get-VMHost -Name $ESXi | Get-VirtualPortGroup -Standard | Get-SecurityPolicy | Set-SecurityPolicy -ForgedTransmitsInherited $true

See Also

https://github.com/vmware/vcf-security-and-compliance-guidelines/raw/refs/heads/main/security-configuration-hardening-guide/vsphere/8.0/