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Secure on-premises computer accounts with Active Directory

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A computer account, or LocalSystem account, is highly privileged with access to almost all resources on the local computer. The account isn't associated with signed-on user accounts. Services run as LocalSystem access network resources by presenting the computer credentials to remote servers in the format <domain_name>\\<computer_name>$. The computer account predefined name is NT AUTHORITY\SYSTEM. You can start a service and provide security context for that service.

Screenshot of a list of local services on a computer account.

Benefits of using a computer account

A computer account has the following benefits:

  • Unrestricted local access - the computer account provides complete access to the machine's local resources
  • Automatic password management - removes the need for manually changed passwords. The account is a member of Active Directory, and its password is changed automatically. With a computer account, there's no need to register the service principal name.
  • Limited access rights off-machine - the default access-control list in Active Directory Domain Services (AD DS) permits minimal access to computer accounts. During access by an unauthorized user, the service has limited access to network resources.

Computer account security-posture assessment

Use the following table to review potential computer-account issues and mitigations.

Computer-account issue Mitigation
Computer accounts are subject to deletion and re-creation when the computer leaves and rejoins the domain. Confirm the requirement to add a computer to an Active Directory group. To verify computer accounts added to a group, use the scripts in the following section.
If you add a computer account to a group, services that run as LocalSystem on that computer get group access rights. Be selective about computer-account group memberships. Don't make a computer account a member of a domain administrator group. The associated service has complete access to AD DS.
Inaccurate network defaults for LocalSystem. Don't assume the computer account has the default limited access to network resources. Instead, confirm group memberships for the account.
Unknown services that run as LocalSystem. Ensure services that run under the LocalSystem account are Microsoft services, or trusted services.

Find services and computer accounts

To find services that run under the computer account, use the following PowerShell cmdlet:

Get-WmiObject win32_service | select Name, StartName | Where-Object {($_.StartName -eq "LocalSystem")}

To find computer accounts that are members of a specific group, run the following PowerShell cmdlet:

Get-ADComputer -Filter {Name -Like "*"} -Properties MemberOf | Where-Object {[STRING]$_.MemberOf -like "Your_Group_Name_here*"} | Select Name, MemberOf

To find computer accounts that are members of identity administrators groups (domain administrators, enterprise administrators, and administrators), run the following PowerShell cmdlet:

Get-ADGroupMember -Identity Administrators -Recursive | Where objectClass -eq "computer"

Computer account recommendations

Important

Computer accounts are highly privileged, therefore use them if your service requires unrestricted access to local resources, on the machine, and you can't use a managed service account (MSA).

  • Confirm the service owner's service runs with an MSA
  • Use a group managed service account (gMSA), or a standalone managed service account (sMSA), if your service supports it
  • Use a domain user account with the permissions needed to run the service

Next steps

To learn more about securing service accounts, see the following articles: