Disable new DMA devices when this computer is locked

ComputerNeeds changes for IntuneNew in 22H2 · 1.0DisableExternalDMAUnderLock_Name

Supported on At least Windows Server 2016, Windows 10 Version 1703

22H2 · 1.0

What it does

This policy setting allows you to block direct memory access (DMA) for all Thunderbolt hot pluggable PCI downstream ports until a user logs into Windows. Once a user logs in, Windows will enumerate the PCI devices connected to the host Thunderbolt PCI ports. Every time the user locks the machine, DMA will be blocked on hot plug Thunderbolt PCI ports with no children devices, until the user logs in again. Devices which were already enumerated when the machine was unlocked will continue to function until unplugged or the system is rebooted or hibernated. This policy setting is only enforced when BitLocker or device encryption is enabled. Note: Some PCs may not be compatible with this policy if the system firmware enables DMA for newly attached Thunderbolt devices before exposing the new devices to Windows.

What it writes

Hive: HKEY_LOCAL_MACHINE
Registry key: Software\Policies\Microsoft\FVE
Value name: DisableExternalDMAUnderLock
When enabled: DWORD 1
When disabled: DWORD 0

Why it needs changes for Intune

Policy references a Windows supportedOn definition.
ADMX-INTUNE-WINDOWS-SUPPORTEDON-REFERENCE

In Intune

No native CSP; import the ADMX (needs changes first).

From Microsoft's Policy CSP DDF files (DDF v2 Files, February 2026), read 18 Oct 2026.

Security baselines

Microsoft's Windows 10 version 22H2 Security Baseline sets this to Enabled, in its GPO “MSFT Windows 10 22H2 - BitLocker”.

Policy value DisableExternalDMAUnderLock: Sets DisableExternalDMAUnderLock to 1 (REG_DWORD).

Read from the registry.pol files in the baselines' GPO backups, downloaded from Microsoft's Security Compliance Toolkit. All baselines

Configure and deploy

Choose a state; the output below is generated from the template for exactly that.

Enabled · Computer · template defaults

Registry file (.reg)

Windows Registry Editor Version 5.00

[HKEY_LOCAL_MACHINE\Software\Policies\Microsoft\FVE]
"DisableExternalDMAUnderLock"=dword:00000001

PowerShell

$ErrorActionPreference = 'Stop'

function Set-RegistryValue {
    param(
        [Parameter(Mandatory = $true)][string] $Path,
        [Parameter(Mandatory = $true)][string] $Name,
        [Parameter(Mandatory = $true)][string] $PropertyType,
        [Parameter(Mandatory = $true)][object] $Value
    )

    if (-not (Test-Path -LiteralPath $Path)) {
        New-Item -Path $Path -Force | Out-Null
    }

    New-ItemProperty -LiteralPath $Path -Name $Name -PropertyType $PropertyType -Value $Value -Force | Out-Null
}

function Remove-RegistryValue {
    param(
        [Parameter(Mandatory = $true)][string] $Path,
        [Parameter(Mandatory = $true)][string] $Name
    )

    if (Test-Path -LiteralPath $Path) {
        Remove-ItemProperty -LiteralPath $Path -Name $Name -Force -ErrorAction SilentlyContinue
    }
}

function Clear-RegistryKeyValues {
    param(
        [Parameter(Mandatory = $true)][string] $Path
    )

    if (-not (Test-Path -LiteralPath $Path)) {
        return
    }

    foreach ($propertyName in (Get-Item -LiteralPath $Path).Property) {
        Remove-ItemProperty -LiteralPath $Path -Name $propertyName -Force -ErrorAction SilentlyContinue
    }
}

# Policy: Disable new DMA devices when this computer is locked
# Name: DisableExternalDMAUnderLock_Name
# Scope: Machine
# State: Enabled
# Source: VolumeEncryption.admx

Set-RegistryValue -Path 'Registry::HKEY_LOCAL_MACHINE\Software\Policies\Microsoft\FVE' -Name 'DisableExternalDMAUnderLock' -PropertyType 'DWord' -Value 1

The OMA-URI is an inferred ADMX-backed Policy CSP candidate derived from the source ADMX file name and policy name.
Some Microsoft policies use built-in Policy CSP pages whose area names don't match the ADMX file name, so verify the candidate against Microsoft Learn before deployment.

ADMX profile candidate (OMA-URI)

./Device/Vendor/MSFT/Policy/Config/ADMX_VolumeEncryption/DisableExternalDMAUnderLock_Name

ADMX SyncML candidate

<SyncML xmlns="SYNCML:SYNCML1.2">
  <SyncBody>
    <Replace>
      <CmdID>1</CmdID>
      <Item>
        <Meta>
          <Format>chr</Format>
          <Type>text/plain</Type>
        </Meta>
        <Target>
          <LocURI>./Device/Vendor/MSFT/Policy/Config/ADMX_VolumeEncryption/DisableExternalDMAUnderLock_Name</LocURI>
        </Target>
        <Data>&lt;enabled/&gt;</Data>
      </Item>
    </Replace>
    <Final/>
  </SyncBody>
</SyncML>

Intune remediation scripts

Detection

$ErrorActionPreference = 'Stop'
$reasons = [System.Collections.Generic.List[string]]::new()

function Test-RegistryValueExists {
    param(
        [Parameter(Mandatory = $true)][string] $Path,
        [Parameter(Mandatory = $true)][string] $Name
    )

    if (-not (Test-Path -LiteralPath $Path)) {
        return $false
    }

    return $null -ne (Get-ItemProperty -LiteralPath $Path -Name $Name -ErrorAction SilentlyContinue)
}

function Test-RegistryValueEquals {
    param(
        [Parameter(Mandatory = $true)][string] $Path,
        [Parameter(Mandatory = $true)][string] $Name,
        [Parameter(Mandatory = $true)][string] $Kind,
        [Parameter(Mandatory = $true)][object] $Expected
    )

    if (-not (Test-Path -LiteralPath $Path)) {
        return $false
    }

    $valueObject = Get-ItemProperty -LiteralPath $Path -Name $Name -ErrorAction SilentlyContinue
    if ($null -eq $valueObject) {
        return $false
    }

    $actual = $valueObject.$Name
    switch ($Kind) {
        'String' { return [string]$actual -ceq [string]$Expected }
        'ExpandString' { return [string]$actual -ceq [string]$Expected }
        'DWord' { return [uint32]$actual -eq [uint32]$Expected }
        'QWord' { return [uint64]$actual -eq [uint64]$Expected }
        'MultiString' {
            $actualArray = @($actual)
            $expectedArray = @($Expected)
            if ($actualArray.Count -ne $expectedArray.Count) { return $false }
            for ($index = 0; $index -lt $actualArray.Count; $index++) {
                if ([string]$actualArray[$index] -cne [string]$expectedArray[$index]) { return $false }
            }
            return $true
        }
        'Binary' {
            $actualArray = [byte[]]$actual
            $expectedArray = [byte[]]$Expected
            if ($actualArray.Length -ne $expectedArray.Length) { return $false }
            for ($index = 0; $index -lt $actualArray.Length; $index++) {
                if ($actualArray[$index] -ne $expectedArray[$index]) { return $false }
            }
            return $true
        }
        default { return [string]$actual -ceq [string]$Expected }
    }
}

# Policy: Disable new DMA devices when this computer is locked
# Name: DisableExternalDMAUnderLock_Name
# Scope: Machine
# State: Enabled
# Source: VolumeEncryption.admx

$isMatch = Test-RegistryValueEquals -Path 'Registry::HKEY_LOCAL_MACHINE\Software\Policies\Microsoft\FVE' -Name 'DisableExternalDMAUnderLock' -Kind 'DWord' -Expected 1
if (-not $isMatch) {
    $reasons.Add('Value mismatch: HKEY_LOCAL_MACHINE\Software\Policies\Microsoft\FVE\DisableExternalDMAUnderLock') | Out-Null
}

if ($reasons.Count -eq 0) {
    Write-Output 'Compliant'
    exit 0
}

$reasons | ForEach-Object { Write-Output $_ }
exit 1

Remediation

$ErrorActionPreference = 'Stop'

function Set-RegistryValue {
    param(
        [Parameter(Mandatory = $true)][string] $Path,
        [Parameter(Mandatory = $true)][string] $Name,
        [Parameter(Mandatory = $true)][string] $PropertyType,
        [Parameter(Mandatory = $true)][object] $Value
    )

    if (-not (Test-Path -LiteralPath $Path)) {
        New-Item -Path $Path -Force | Out-Null
    }

    New-ItemProperty -LiteralPath $Path -Name $Name -PropertyType $PropertyType -Value $Value -Force | Out-Null
}

function Remove-RegistryValue {
    param(
        [Parameter(Mandatory = $true)][string] $Path,
        [Parameter(Mandatory = $true)][string] $Name
    )

    if (Test-Path -LiteralPath $Path) {
        Remove-ItemProperty -LiteralPath $Path -Name $Name -Force -ErrorAction SilentlyContinue
    }
}

function Clear-RegistryKeyValues {
    param(
        [Parameter(Mandatory = $true)][string] $Path
    )

    if (-not (Test-Path -LiteralPath $Path)) {
        return
    }

    foreach ($propertyName in (Get-Item -LiteralPath $Path).Property) {
        Remove-ItemProperty -LiteralPath $Path -Name $propertyName -Force -ErrorAction SilentlyContinue
    }
}

# Policy: Disable new DMA devices when this computer is locked
# Name: DisableExternalDMAUnderLock_Name
# Scope: Machine
# State: Enabled
# Source: VolumeEncryption.admx

Set-RegistryValue -Path 'Registry::HKEY_LOCAL_MACHINE\Software\Policies\Microsoft\FVE' -Name 'DisableExternalDMAUnderLock' -PropertyType 'DWord' -Value 1

History 2 retained releases

22H2 · 1.015 Jul 2024
- Added in this release.

Template

Internal name: DisableExternalDMAUnderLock_Name
Namespace: Microsoft.Policies.VolumeEncryption
Template file: VolumeEncryption.admx
Release: Windows 10 22H2 · 1.0 · file set bc15f6a5271783ee…

Definition, editor controls and support

Definition

<policy class="Machine" displayName="$(string.DisableExternalDMAUnderLock_Name)" explainText="$(string.DisableExternalDMAUnderLock_Help)" key="Software\Policies\Microsoft\FVE" name="DisableExternalDMAUnderLock_Name" valueName="DisableExternalDMAUnderLock" xmlns="http://schemas.microsoft.com/GroupPolicy/2006/07/PolicyDefinitions">
      <parentCategory ref="Microsoft.Policies.VolumeEncryption:FVECategory" />
       <supportedOn ref="Microsoft.Policies.Windows:SUPPORTED_Windows_10_0_RS2" />

      <enabledValue>
        <decimal value="1" />
      </enabledValue>
      <disabledValue>
        <decimal value="0" />
      </disabledValue>
    </policy>

Editor controls

Supported platforms and category

Microsoft.Policies.Products:product:MicrosoftWindows
sha256:4b3cb6917b5e5b7cd142c0157f10882786b3e9ee67c29fd7b8f4c6cb2eec5fe7
Microsoft.Policies.VolumeEncryption:category:FVECategory
<category displayName="$(string.FVECategory)" name="FVECategory" xmlns="http://schemas.microsoft.com/GroupPolicy/2006/07/PolicyDefinitions">
      <parentCategory ref="Microsoft.Policies.Windows:WindowsComponents" />
    </category>
Microsoft.Policies.Windows:category:WindowsComponents
<category displayName="$(string.WindowsComponents)" explainText="$(string.WindowsComponents_Help)" name="WindowsComponents" xmlns="http://schemas.microsoft.com/GroupPolicy/2006/07/PolicyDefinitions" />
Microsoft.Policies.Windows:definition:SUPPORTED_Windows_10_0_RS2
<definition displayName="$(string.SUPPORTED_Windows_10_0_RS2)" name="SUPPORTED_Windows_10_0_RS2" xmlns="http://schemas.microsoft.com/GroupPolicy/2006/07/PolicyDefinitions">
          <or>
              <range minVersionIndex="13" ref="Microsoft.Policies.Products:MicrosoftWindows" />
          </or>
      </definition>
Microsoft.Policies.Products:product:MicrosoftWindows
<product displayName="$(string.MicrosoftWindows)" name="MicrosoftWindows" xmlns="http://schemas.microsoft.com/GroupPolicy/2006/07/PolicyDefinitions">
        <majorVersion displayName="$(string.MicrosoftWindows2000)" name="MicrosoftWindows2000" versionIndex="1">
          <minorVersion displayName="$(string.MicrosoftWindows2000_RTM)" name="MicrosoftWindows2000_RTM" versionIndex="0" />
          <minorVersion displayName="$(string.MicrosoftWindows2000_SP1)" name="MicrosoftWindows2000_SP1" versionIndex="1" />
          <minorVersion displayName="$(string.MicrosoftWindows2000_SP2)" name="MicrosoftWindows2000_SP2" versionIndex="2" />
          <minorVersion displayName="$(string.MicrosoftWindows2000_SP3)" name="MicrosoftWindows2000_SP3" versionIndex="3" />
          <minorVersion displayName="$(string.MicrosoftWindows2000_SP4)" name="MicrosoftWindows2000_SP4" versionIndex="4" />
        </majorVersion>
        <majorVersion displayName="$(string.MicrosoftWindowsXP)" name="MicrosoftWindowsXP" versionIndex="2">
          <minorVersion displayName="$(string.MicrosoftWindowsXP_RTM)" name="MicrosoftWindowsXP_RTM" versionIndex="0" />
          <minorVersion displayName="$(string.MicrosoftWindowsXP_SP1)" name="MicrosoftWindowsXP_SP1" versionIndex="1" />
          <minorVersion displayName="$(string.MicrosoftWindowsXP_SP2)" name="MicrosoftWindowsXP_SP2" versionIndex="2" />
        </majorVersion>
        <majorVersion displayName="$(string.MicrosoftWindowsServer2003)" name="MicrosoftWindowsServer2003" versionIndex="3">
          <minorVersion displayName="$(string.MicrosoftWindowsServer2003_RTM)" name="MicrosoftWindowsServer2003_RTM" versionIndex="0" />
          <minorVersion displayName="$(string.MicrosoftWindowsServer2003_SP1)" name="MicrosoftWindowsServer2003_SP1" versionIndex="1" />
          <minorVersion displayName="$(string.MicrosoftWindowsServer2003_R2)" name="MicrosoftWindowsServer2003_R2" versionIndex="2" />
          <minorVersion displayName="$(string.MicrosoftWindowsServer2003_SP2)" name="MicrosoftWindowsServer2003_SP2" versionIndex="3" />
        </majorVersion>
        <majorVersion displayName="$(string.MicrosoftWindowsVista)" name="MicrosoftWindowsVista" versionIndex="4">
          <minorVersion displayName="$(string.MicrosoftWindowsVista_RTM)" name="MicrosoftWindowsVista_RTM" versionIndex="0" />
          <minorVersion displayName="$(string.MicrosoftWindowsVista_SP1)" name="MicrosoftWindowsVista_SP1" versionIndex="1" />
        </majorVersion>
        <majorVersion displayName="$(string.WindowsServer2008)" name="WindowsServer2008" versionIndex="5">
          <minorVersion displayName="$(string.WindowsServer2008_RTM)" name="WindowsServer2008_RTM" versionIndex="0" />
          <minorVersion displayName="$(string.WindowsServer2008_R2)" name="WindowsServer2008_R2" versionIndex="1" />
        </majorVersion>
        <majorVersion displayName="$(string.MicrosoftWindows7)" name="MicrosoftWindows7" versionIndex="6">
          <minorVersion displayName="$(string.MicrosoftWindows7_RTM)" name="MicrosoftWindows7_RTM" versionIndex="0" />
        </majorVersion>
        <majorVersion displayName="$(string.MicrosoftWindowsServer8)" name="MicrosoftWindowsServer8" versionIndex="7">
           <minorVersion displayName="$(string.MicrosoftWindowsServer8_RTM)" name="MicrosoftWindowsServer8_RTM" versionIndex="0" />
        </majorVersion>
        <majorVersion displayName="$(string.MicrosoftWindows8)" name="MicrosoftWindows8" versionIndex="8">
          <minorVersion displayName="$(string.MicrosoftWindows8_RTM)" name="MicrosoftWindows8_RTM" versionIndex="0" />
        </majorVersion>
        <majorVersion displayName="$(string.MicrosoftWindows_RT)" name="MicrosoftWindows_RT" versionIndex="9">
          <minorVersion displayName="$(string.MicrosoftWindows_RT_RTM)" name="MicrosoftWindows_RT_RTM" versionIndex="0" />
        </majorVersion>
        <majorVersion displayName="$(string.MicrosoftWindowsServer_6_3)" name="MicrosoftWindowsServer_6_3" versionIndex="10">
           <minorVersion displayName="$(string.MicrosoftWindowsServer_6_3_RTM)" name="MicrosoftWindowsServer_6_3_RTM" versionIndex="0" />
        </majorVersion>
        <majorVersion displayName="$(string.MicrosoftWindows_6_3)" name="MicrosoftWindows_6_3" versionIndex="11">
          <minorVersion displayName="$(string.MicrosoftWindows_6_3_RTM)" name="MicrosoftWindows_6_3_RTM" versionIndex="0" />
        </majorVersion>
        <majorVersion displayName="$(string.MicrosoftWindows_6_3_RT)" name="MicrosoftWindows_6_3_RT" versionIndex="12">
            <minorVersion displayName="$(string.MicrosoftWindows_6_3_RT_RTM)" name="MicrosoftWindows_6_3_RT_RTM" versionIndex="0" />
        </majorVersion>
        <majorVersion displayName="$(string.MicrosoftWindowsServer_10_0)" name="MicrosoftWindowsServer_10_0" versionIndex="13">
            <minorVersion displayName="$(string.MicrosoftWindowsServer_10_0_RTM)" name="MicrosoftWindowsServer_10_0_RTM" versionIndex="0" />
          </majorVersion>
        <majorVersion displayName="$(string.MicrosoftWindows_10_0)" name="MicrosoftWindows_10_0" versionIndex="14">
            <minorVersion displayName="$(string.MicrosoftWindows_10_0_RTM)" name="MicrosoftWindows_10_0_RTM" versionIndex="0" />
        </majorVersion>
        <majorVersion displayName="$(string.MicrosoftWindows_10_0_RT)" name="MicrosoftWindows_10_0_RT" versionIndex="15">
            <minorVersion displayName="$(string.MicrosoftWindows_10_0_RT_RTM)" name="MicrosoftWindows_10_0_RT_RTM" versionIndex="0" />
        </majorVersion>
      </product>
<strings><string id="Microsoft.Policies.Products:MicrosoftWindows">Windows operating system</string><string id="Microsoft.Policies.Products:MicrosoftWindows2000">Windows 2000 operating systems</string><string id="Microsoft.Policies.Products:MicrosoftWindows2000_RTM">Windows 2000</string><string id="Microsoft.Policies.Products:MicrosoftWindows2000_SP1">Windows 2000 Service Pack 1</string><string id="Microsoft.Policies.Products:MicrosoftWindows2000_SP2">Windows 2000 Service Pack 2</string><string id="Microsoft.Policies.Products:MicrosoftWindows2000_SP3">Windows 2000 Service Pack 3</string><string id="Microsoft.Policies.Products:MicrosoftWindows2000_SP4">Windows 2000 Service Pack 4</string><string id="Microsoft.Policies.Products:MicrosoftWindows7">Windows 7 operating systems</string><string id="Microsoft.Policies.Products:MicrosoftWindows7_RTM">Windows 7</string><string id="Microsoft.Policies.Products:MicrosoftWindows8">Windows 8 operating systems</string><string id="Microsoft.Policies.Products:MicrosoftWindows8_RTM">Windows 8</string><string id="Microsoft.Policies.Products:MicrosoftWindowsServer2003">Windows Server 2003 operating systems</string><string id="Microsoft.Policies.Products:MicrosoftWindowsServer2003_R2">Windows Server 2003 R2</string><string id="Microsoft.Policies.Products:MicrosoftWindowsServer2003_RTM">Windows Server 2003</string><string id="Microsoft.Policies.Products:MicrosoftWindowsServer2003_SP1">Windows Server 2003 Service Pack 1</string><string id="Microsoft.Policies.Products:MicrosoftWindowsServer2003_SP2">Windows Server 2003 Service Pack 2</string><string id="Microsoft.Policies.Products:MicrosoftWindowsServer8">Windows Server 2012 operating systems</string><string id="Microsoft.Policies.Products:MicrosoftWindowsServer8_RTM">Windows Server 2012</string><string id="Microsoft.Policies.Products:MicrosoftWindowsServer_10_0">Windows Server 2016 operating systems</string><string id="Microsoft.Policies.Products:MicrosoftWindowsServer_10_0_RTM">Windows Server 2016</string><string id="Microsoft.Policies.Products:MicrosoftWindowsServer_6_3">Windows Server 2012 R2 operating systems</string><string id="Microsoft.Policies.Products:MicrosoftWindowsServer_6_3_RTM">Windows Server 2012 R2</string><string id="Microsoft.Policies.Products:MicrosoftWindowsVista">Windows Vista operating systems</string><string id="Microsoft.Policies.Products:MicrosoftWindowsVista_RTM">Windows Vista</string><string id="Microsoft.Policies.Products:MicrosoftWindowsVista_SP1">Windows Vista Service Pack 1</string><string id="Microsoft.Policies.Products:MicrosoftWindowsXP">Windows XP operating systems</string><string id="Microsoft.Policies.Products:MicrosoftWindowsXP_RTM">Windows XP</string><string id="Microsoft.Policies.Products:MicrosoftWindowsXP_SP1">Windows XP Service Pack 1</string><string id="Microsoft.Policies.Products:MicrosoftWindowsXP_SP2">Windows XP Service Pack 2</string><string id="Microsoft.Policies.Products:MicrosoftWindows_10_0">Windows 10 operating systems</string><string id="Microsoft.Policies.Products:MicrosoftWindows_10_0_RT">Windows 10 RT operating systems</string><string id="Microsoft.Policies.Products:MicrosoftWindows_10_0_RTM">Windows 10</string><string id="Microsoft.Policies.Products:MicrosoftWindows_10_0_RT_RTM">Windows 10 RT</string><string id="Microsoft.Policies.Products:MicrosoftWindows_6_3">Windows 8.1 operating systems</string><string id="Microsoft.Policies.Products:MicrosoftWindows_6_3_RT">Windows RT 8.1 operating systems</string><string id="Microsoft.Policies.Products:MicrosoftWindows_6_3_RTM">Windows 8.1</string><string id="Microsoft.Policies.Products:MicrosoftWindows_6_3_RT_RTM">Windows RT 8.1</string><string id="Microsoft.Policies.Products:MicrosoftWindows_RT">Windows RT operating systems</string><string id="Microsoft.Policies.Products:MicrosoftWindows_RT_RTM">Windows RT</string><string id="Microsoft.Policies.Products:WindowsServer2008">Windows Server 2008 operating systems</string><string id="Microsoft.Policies.Products:WindowsServer2008_R2">Windows Server 2008 R2</string><string id="Microsoft.Policies.Products:WindowsServer2008_RTM">Windows Server 2008</string></strings>
Microsoft.Policies.VolumeEncryption:category:FVECategory
<category displayName="$(string.FVECategory)" name="FVECategory" xmlns="http://schemas.microsoft.com/GroupPolicy/2006/07/PolicyDefinitions">
      <parentCategory ref="Microsoft.Policies.Windows:WindowsComponents" />
    </category>
<strings><string id="Microsoft.Policies.VolumeEncryption:FVECategory">BitLocker Drive Encryption</string></strings>
Microsoft.Policies.Windows:category:WindowsComponents
<category displayName="$(string.WindowsComponents)" explainText="$(string.WindowsComponents_Help)" name="WindowsComponents" xmlns="http://schemas.microsoft.com/GroupPolicy/2006/07/PolicyDefinitions" />
<strings><string id="Microsoft.Policies.Windows:WindowsComponents">Windows Components</string><string id="Microsoft.Policies.Windows:WindowsComponents_Help">Contains settings for operating system components.</string></strings>
Microsoft.Policies.Windows:definition:SUPPORTED_Windows_10_0_RS2
<definition displayName="$(string.SUPPORTED_Windows_10_0_RS2)" name="SUPPORTED_Windows_10_0_RS2" xmlns="http://schemas.microsoft.com/GroupPolicy/2006/07/PolicyDefinitions">
          <or>
              <range minVersionIndex="13" ref="Microsoft.Policies.Products:MicrosoftWindows" />
          </or>
      </definition>
<strings><string id="Microsoft.Policies.Windows:SUPPORTED_Windows_10_0_RS2">At least Windows Server 2016, Windows 10 Version 1703</string></strings>