[REQ-PAW-094] Configure User Rights: Act as part of the operating system for PAWs

Target Scope

  • Applicable Systems: Privileged Access Workstations (PAWs) dedicated to Tier 0 and critical administrative functions. (For Tier 2 Client Workstations and Member Servers, refer to standard baseline REQ-END-098). (For Domain Controllers, refer to REQ-DC-105).
  • Operating Systems: Windows 10 Enterprise (1809 and above) and Windows 11 Enterprise.

Implementation Details

  • Priority: High
  • GPO Path / Registry Location:
    • Policy Display Name: Act as part of the operating system
    • Privilege Constant: SeTcbPrivilege
    • GPO Path: Computer Configuration\Policies\Windows Settings\Security Settings\Local Policies\User Rights Assignment\Act as part of the operating system
    • Registry Location: Stored inside local security database under privilege SeTcbPrivilege set to No one (Empty).

Rationale

The SeTcbPrivilege identifies its holder as part of the Trusted Computer Base (TCB)—the core inner ring of the operating system. A process possessing this privilege can register as a trusted logon process with the Local Security Authority via LsaRegisterLogonProcess and invoke LsaLogonUser to create an arbitrary, fully authenticated access token for any user without knowing the user's password or requiring credentials.

1. Technical Threat Vector & Abuse Mechanics

Possession of SeTcbPrivilege by any user or third-party process represents an immediate, complete compromise of the operating system: (1) Universal Token Forgery: An attacker can call LsaLogonUser to request an elevated token for NT AUTHORITY\SYSTEM or any Domain Administrator account, bypassing all authentication safeguards; (2) LSA Impersonation: The attacker can interact directly with LSA authentication packages, intercepting plain-text credentials and injecting rogue security support providers (SSPs); (3) Bypassing Security Auditing: TCB processes can suppress audit logging and bypass Mandatory Integrity Control checks.

2. Architectural Defense & Least Privilege Enforcement

Privileged Access Workstations (PAWs) serve as the clean-source platform for managing Tier 0 Active Directory and cloud infrastructure. Because administrative credentials exist in memory on these devices, strict isolation must be maintained at the operating system level. Restricting this user right strictly prevents lower-tier sessions, third-party software, or interactive users from interfering with administrative operations, upholding the Clean Source Principle and preventing token kidnapping or session hijacking.

This privilege must be strictly configured to No one (Empty). Operating system components that require TCB authority (such as lsass.exe) run under internal system contexts and do not require user-level assignment of SeTcbPrivilege. No human user account, administrative identity, or third-party service account should ever hold this right.

3. MITRE ATT&CK Mapping

  • T1134.001 - Access Token Manipulation: Token Impersonation/Theft
  • T1078 - Valid Accounts
  • T1068 - Exploitation for Privilege Escalation

Legacy Impact & Compatibility

  • Operational Impact: Configuring SeTcbPrivilege to No one aligns with Microsoft Security Baselines and CIS Benchmarks and introduces zero operational disruption. No legitimate modern enterprise application requires assignment of this privilege. Any assignment or use of SeTcbPrivilege triggers immediate high-severity security alerts (Security Event ID 4704).

Implementation Steps

Option A: Group Policy Object (GPO) Configuration (Preferred)

  1. Open the Group Policy Management Console (gpmc.msc).
  2. Navigate to the targeted GPO linked to Tier 0 PAW systems (e.g., GPO_Hardening_PAW).
  3. In the console tree, browse to: Computer Configuration\Policies\Windows Settings\Security Settings\Local Policies\User Rights Assignment
  4. Open the policy Act as part of the operating system.
  5. Select the Define these policy settings check box.
  6. Click Add User or Group... and ensure the principal list is empty (or remove all assigned accounts/groups so that no principals are configured).
  7. Click Apply and OK.
  8. Apply and verify policy enforcement across target hosts using gpupdate /force and inspect with secedit /export /cfg C:\Windows\Temp\sec_audit.cfg.

Option B: PowerShell & Registry Configuration (Remediation / Non-GPO)

Download Script: Configure-PawUraSeTcbPrivilege.ps1

# Configure-PawUraSeTcbPrivilege.ps1
# Configure-PawUraSeTcbPrivilege.ps1
$SecTempDir = Join-Path $env:TEMP "SecurityTemplates"
if (-not (Test-Path $SecTempDir)) { New-Item -Path $SecTempDir -ItemType Directory -Force | Out-Null }
$CfgFile = Join-Path $SecTempDir "ura_setcbprivilege.cfg"
$DbFile = Join-Path $SecTempDir "secedit_setcbprivilege.sdb"
$LogFile = Join-Path $SecTempDir "secedit.log"

$Process = Start-Process secedit -ArgumentList "/export /cfg `"$CfgFile`"" -Wait -NoNewWindow -PassThru
if ($Process.ExitCode -ne 0) { Throw "Failed to export security template" }

$ConfigText = Get-Content -Path $CfgFile -Raw
if ($ConfigText -notmatch "\[Privilege Rights\]") {
    $ConfigText += "`r`n[Privilege Rights]`r`n"
}

$Lines = $ConfigText -split "`r?`n"
$NewLines = @()
$InPriv = $false
$KeyAdded = $false

foreach ($Line in $Lines) {
    if ($Line -match "^\[(.*)\]$") {
        if ($Matches[1] -eq "Privilege Rights") {
            $InPriv = $true
        } else {
            $InPriv = $false
        }
    }
    if ($InPriv -and $Line -match "^\s*SeTcbPrivilege\s*=") {
        $NewLines += "SeTcbPrivilege = "
        $KeyAdded = $true
    } else {
        $NewLines += $Line
    }
}

if (-not $KeyAdded) {
    # Find Privilege Rights section index and insert it right after
    $Idx = $NewLines.IndexOf("[Privilege Rights]")
    if ($Idx -ge 0) {
        $NewLines.Insert($Idx + 1, "SeTcbPrivilege = ")
    } else {
        $NewLines += "SeTcbPrivilege = "
    }
}

$NewLines | Set-Content -Path $CfgFile -Force
$Proc = Start-Process secedit -ArgumentList "/configure /db `"$DbFile`" /cfg `"$CfgFile`" /areas USER_RIGHTS /log `"$LogFile`"" -Wait -NoNewWindow -PassThru
if ($Proc.ExitCode -ne 0) { Throw "Failed to configure secedit user rights" }
Remove-Item -Path $CfgFile, $DbFile -ErrorAction SilentlyContinue

To audit the hardening status: Download Script: Get-PawUraSeTcbPrivilegeStatus.ps1

# Get-PawUraSeTcbPrivilegeStatus.ps1
# Get-PawUraSeTcbPrivilegeStatus.ps1
$SecTempDir = Join-Path $env:TEMP "SecurityTemplates"
if (-not (Test-Path $SecTempDir)) { New-Item -Path $SecTempDir -ItemType Directory -Force | Out-Null }
$CfgFile = Join-Path $SecTempDir "ura_audit_setcbprivilege.cfg"

$Process = Start-Process secedit -ArgumentList "/export /cfg `"$CfgFile`"" -Wait -NoNewWindow -PassThru
if ($Process.ExitCode -ne 0) {
    Write-Output "Non-Compliant"
    exit 1
}

$ConfigText = Get-Content -Path $CfgFile -Raw
Remove-Item -Path $CfgFile -ErrorAction SilentlyContinue

$Match = $ConfigText -match "(?mi)^\s*SeTcbPrivilege\s*=\s*(.*)$"
$CurrentValue = ""
if ($Match) {
    $CurrentValue = $Matches[1].Trim()
}

$Expected = ""
if ($CurrentValue -eq $Expected) {
    Write-Output "Compliant"
    exit 0
} else {
    Write-Output "Non-Compliant"
    exit 1
}

Sources & Compliance References

  • ANSSI Active Directory Hardening Guide: ANSSI Active Directory Hardening Guide: R28 (User Rights Assignment)
  • CIS Benchmark: 2.2.5 (L1) Ensure 'Act as part of the operating system' is set to 'No One'
  • Microsoft Security Baseline: User Rights Configuration specifications
  • Microsoft Learn: User Rights Assignment Reference

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