The domain functional level must be at a Windows Server version still supported by Microsoft.

Severity	Group ID	Group Title	Version	Rule ID	Date	STIG Version
medium	V-243480	SRG-OS-000480	AD.0160	SV-243480r959010_rule	2024-09-13	3

Description
Domains operating at functional levels below Windows Server versions no longer supported by Microsoft reduce the level of security in the domain and forest as advanced features of the directory are not available. This also prevents the addition of domain controllers to the domain using Windows Server versions prior to the current domain functional level.

ℹ️ Check
Open "Active Directory Domains and Trusts" (run "domain.msc") or "Active Directory Users and Computers" (run "dsa.msc"). Right-click in the left pane on the name of the Domain being reviewed. Select "Raise domain functional level..." The current domain functional level will be displayed (as well as the option to raise the domain functional level). Select "Cancel" to exit. Alternately, using PowerShell (Windows Server 2016): Select "Active Directory Module for Windows PowerShell", available in Administrative Tools or the Start Screen. Run "Get-ADDomain". View the value for "DomainMode:" If the domain functional level is not Windows Server 2016, this is a finding. Using the highest domain functional level supported by the domain controllers is recommended.

ℹ️ Check

Open "Active Directory Domains and Trusts" (run "domain.msc") or "Active Directory Users and Computers" (run "dsa.msc"). Right-click in the left pane on the name of the Domain being reviewed. Select "Raise domain functional level..." The current domain functional level will be displayed (as well as the option to raise the domain functional level). Select "Cancel" to exit. Alternately, using PowerShell (Windows Server 2016): Select "Active Directory Module for Windows PowerShell", available in Administrative Tools or the Start Screen. Run "Get-ADDomain". View the value for "DomainMode:" If the domain functional level is not Windows Server 2016, this is a finding. Using the highest domain functional level supported by the domain controllers is recommended.

✔️ Fix
Raise the domain functional level to Windows Server 2016. Using the highest domain functional level supported by the domain controllers is recommended. Raising the domain functional level needs to be carefully planned and implemented. This prevents the addition of domain controllers to the domain using Windows versions prior to the current domain functional level. Refer to Microsoft documentation for the process and requirements of raising the domain functional level.

✔️ Fix

Raise the domain functional level to Windows Server 2016. Using the highest domain functional level supported by the domain controllers is recommended. Raising the domain functional level needs to be carefully planned and implemented. This prevents the addition of domain controllers to the domain using Windows versions prior to the current domain functional level. Refer to Microsoft documentation for the process and requirements of raising the domain functional level.