PARENT_OU

Summary

FSProtect ACL Alias	PARENT_OU
Affected Object Types	Organizational Units
Exploitation Certainty	Unlikely

Description

PARENT_OU in Active Directory describes a hierarchical relationship where an Organizational Unit (OU) contains other OUs. This establishes an administrative boundary that affects inheritance, delegation, and policy application. The parent-child structure helps administrators organize directory objects logically to reflect business units or management responsibilities, enabling efficient management of users, computers, and resources across the organization.

However, the PARENT_OU relationship can introduce security risks if it is not managed correctly. An attacker who gains administrative control over a parent OU effectively controls all child OUs in the hierarchy, potentially impacting hundreds or thousands of user accounts, computer objects, and security settings with a single compromise. Misconfigured inheritance settings can also unintentionally expose sensitive objects to excessive permissions or apply policies too broadly.

Identification

PowerShell

Active Directory module

Using the Active Directory PowerShell module, you can enumerate PARENT_OU entries.

1. Find-PARENT_OU function

function Find-PARENT_OU {
    [CmdletBinding()]
    param ([string]$CsvPath = ".\PARENT_OU.csv",[string]$Target = "*" )
    Import-Module ActiveDirectory -ErrorAction Stop
    $ous = Get-ADOrganizationalUnit -Filter { Name -like $Target } -Properties DistinguishedName
    $ouList = @()
    foreach ($ou in $ous) {
        $dnParts = $ou.DistinguishedName -split ","

        if ($dnParts.Count -gt 1 -and $dnParts[1] -match "^OU=") {
            $parentOU = $dnParts[1..($dnParts.Count - 1)] -join ","

            $ouList += [PSCustomObject]@{
                OUName    = $ou.Name
                ParentOU  = $parentOU
                DN        = $ou.DistinguishedName
            }
        }
    }
    $ouList | Export-Csv -Path $CsvPath -NoTypeInformation -Encoding UTF8
}

2. Scan all OUs in the domain

Find-PARENT_OU

3. Scan a specific OU

Find-PARENT_OU -Target "USSQLAdmins"

.NET Directory Services

By leveraging PowerShell’s built-in .NET System.DirectoryServices namespace, you can enumerate PARENT_OU entries without relying on external modules or dependencies.

1. Find-PARENT_OUSimple function

function Find-PARENT_OUSimple {
    [CmdletBinding()]
    param( [string]$CsvPath = ".\PARENT_OU.csv",[string]$Target = $null)
    if ($Target) {
        try {
            $ous = @( New-Object System.DirectoryServices.DirectoryEntry("LDAP://$Target") )
        } catch { Write-Error "Failed to bind to '$Target': $_" ; return }
    }
    else {
        try {
            $root   = New-Object System.DirectoryServices.DirectoryEntry("LDAP://RootDSE")
            $baseDN = $root.Properties["defaultNamingContext"].Value
            $searchRoot = New-Object System.DirectoryServices.DirectoryEntry("LDAP://$baseDN")
            $searcher = [System.DirectoryServices.DirectorySearcher]::new($searchRoot)
            $searcher.Filter   = "(objectCategory=organizationalUnit)"
            $searcher.PageSize = 1000
            [void]$searcher.PropertiesToLoad.Add("distinguishedName")
            [void]$searcher.PropertiesToLoad.Add("name")
            $hits = $searcher.FindAll()
            $ous = foreach ($hit in $hits) {
                try { $hit.GetDirectoryEntry() }
                catch { Write-Warning "Could not bind OU: $_"; continue }
            }
        }
        catch { Write-Error "LDAP enumeration failed: $_" ;return}
    }
    $ouList = @()
    foreach ($ou in $ous) {
        $dnParts = $ou.distinguishedName -split ","
        if ($dnParts.Count -gt 1 -and $dnParts[1] -match "^OU=") {
            $parentOU = $dnParts[1..($dnParts.Count - 1)] -join ","
            $ouList += [PSCustomObject]@{
                OUName   = $ou.Properties["name"][0]
                ParentOU = $parentOU.ToString()
                DN       = $ou.distinguishedName.ToString()
            }
        }
    }
    if ($ouList) { $ouList | Export-Csv -Path $CsvPath -NoTypeInformation -Encoding UTF8 }
}

2. Scan all OUs in the domain

Find-PARENT_OUSimple

3. Scan a specific OU

Find-PARENT_OU -Target "OU=USSQLAdmins,OU=SQLServers,DC=Forestall,DC=labs"

Active Directory Users and Computers

1. Launch Active Directory Users and Computers (dsa.msc).

2. In the left navigation pane, expand the domain tree by clicking the > icons.

3. Locate your target OU by navigating through the folder hierarchy.

4. The parent OU is the folder that directly contains your target OU.

5. You can read the full parent hierarchy from the tree structure (each containing folder represents a parent level).

Exploitation

The PARENT_OU relationship only describes the hierarchy between OUs in Active Directory. There is no direct exploitation path.

However, if an attacker compromises a parent OU that has been delegated administrative rights, they can indirectly affect all child OUs, potentially gaining control over users, computers, and policies beneath it.

Mitigation

You can mitigate risks related to PARENT_OU by following these steps:

1. Open Active Directory Users and Computers (dsa.msc).

2. Navigate to the child OU you want to move out of its parent OU.

3. Right-click the child OU and select "Properties".

4. Go to the "Object" tab.

5. If selected, uncheck the "Protect object from accidental deletion" checkbox.

6. Click "Apply" and then "OK" to save the change.

7. Right-click the child OU again and select "Move...".

8. In the "Move" dialog, navigate to the destination where you want to place the OU.

9. Select the destination and click "OK".

10. Verify that the OU has been successfully moved to the new location in the directory tree.

11. Consider re-enabling the "Protect object from accidental deletion" checkbox on the moved OU for protection.

Detection

Adding new Access Control Entries on Active Directory objects changes the ntSecurityDescriptor attribute of the objects themselves. These changes can be detected with Event IDs 5136 and 4662 and can help identify dangerous modifications.

Event ID	Description	Fields/Attributes	References
5136	A directory service object was modified.	ntSecurityDescriptor	https://learn.microsoft.com/en-us/windows/security/threat-protection/auditing/event-5136
4662	An operation was performed on an object.	AccessList, AccessMask	https://learn.microsoft.com/en-us/windows/security/threat-protection/auditing/event-4662

References

Active Directory OU & Security Groups - University of Arkansas

Creating an Organizational Unit Design - Microsoft Learn