Force file extension to match file type

UserNeeds changes for IntuneL_Forcefileextenstionstomatch

Supported on SUPPORTED_Windows7 (defined in the Windows templates)

5568.1000

What it does

This policy setting controls how Excel loads file types that do not match their extension. Excel can load files with extensions that do not match the files' type. For example, if a comma-separated values (CSV) file named example.csv is renamed example.xls (or any other file extension supported by Excel 2003 and earlier only), Excel can properly load it as a CSV file. If you enable this policy setting, you can choose from three options for working with files that have non-matching extensions: - Allow different - Excel opens the files properly without warning users that the files have non-matching extensions. If users subsequently edit and save the files, Excel preserves both the true, underlying file format and the incorrect file extension. - Allow different, but warn - Excel opens the files properly, but warns users about the file type mismatch. This option is the default configuration in Excel. - Always match file type - Excel does not open any files that have non-matching extensions. If you disable or do not configure this policy setting, if users attempt to open files with the wrong extension, Excel opens the file and displays a warning that the file type is not what Excel expected.

What it writes

Hive: HKEY_CURRENT_USER
Registry key: software\policies\microsoft\office\16.0\excel\security

Why it needs changes for Intune

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

Security baselines

Microsoft's Microsoft 365 Apps for Enterprise 2512 sets this to Enabled, in its GPO “MSFT Microsoft 365 Apps v2512 - User”.

extensionhardening: Set to “Always match file type” (2).

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

Options

Option	Type	Registry value	Allowed values
L_EmptyDefault: Allow different, but warn	Drop-down list	`extensionhardening`	Allow different`0` Allow different, but warn`1` Always match file type`2`

Configure and deploy

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

Enabled · User · template defaults

Registry file (.reg)

Windows Registry Editor Version 5.00

[HKEY_CURRENT_USER\software\policies\microsoft\office\16.0\excel\security]
"extensionhardening"=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: Force file extension to match file type
# Name: L_Forcefileextenstionstomatch
# Scope: User
# State: Enabled
# Source: excel16.admx

Set-RegistryValue -Path 'Registry::HKEY_CURRENT_USER\software\policies\microsoft\office\16.0\excel\security' -Name 'extensionhardening' -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)

./User/Vendor/MSFT/Policy/Config/ADMX_excel16/L_Forcefileextenstionstomatch

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>./User/Vendor/MSFT/Policy/Config/ADMX_excel16/L_Forcefileextenstionstomatch</LocURI>
        </Target>
        <Data>&lt;enabled/&gt;
&lt;data id="L_Empty" value="1"/&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: Force file extension to match file type
# Name: L_Forcefileextenstionstomatch
# Scope: User
# State: Enabled
# Source: excel16.admx

$isMatch = Test-RegistryValueEquals -Path 'Registry::HKEY_CURRENT_USER\software\policies\microsoft\office\16.0\excel\security' -Name 'extensionhardening' -Kind 'DWord' -Expected 1
if (-not $isMatch) {
    $reasons.Add('Value mismatch: HKEY_CURRENT_USER\software\policies\microsoft\office\16.0\excel\security\extensionhardening') | 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: Force file extension to match file type
# Name: L_Forcefileextenstionstomatch
# Scope: User
# State: Enabled
# Source: excel16.admx

Set-RegistryValue -Path 'Registry::HKEY_CURRENT_USER\software\policies\microsoft\office\16.0\excel\security' -Name 'extensionhardening' -PropertyType 'DWord' -Value 1

History 1 retained release

5568.100010 Aug 2026
- Already present in the first release ChangeIntel keeps.

Template

Internal name: L_Forcefileextenstionstomatch
Namespace: excel16.Office.Microsoft.Policies.Windows
Template file: excel16.admx
Release: Microsoft 365 Apps 5568.1000 · file set 8be05d876aae137d…

Definition, editor controls and support

Definition

<policy Area="Security Baseline" AreaCategory="File handling" class="User" displayName="$(string.L_Forcefileextenstionstomatch)" explainText="$(string.L_ForcefileextenstionstomatchExplain)" key="software\policies\microsoft\office\16.0\excel\security" name="L_Forcefileextenstionstomatch" presentation="$(presentation.L_Forcefileextenstionstomatch)" xmlns="http://schemas.microsoft.com/GroupPolicy/2006/07/PolicyDefinitions">
      <parentCategory ref="excel16.Office.Microsoft.Policies.Windows:L_Security" />
      <supportedOn ref="Microsoft.Policies.Windows:SUPPORTED_Windows7" />
      <elements>
        <enum id="L_Empty" valueName="extensionhardening">
          <item displayName="$(string.L_Allowdifferent)">
            <value>
              <decimal value="0" />
            </value>
          </item>
          <item displayName="$(string.L_Allowdifferentbutwarn)">
            <value>
              <decimal value="1" />
            </value>
          </item>
          <item displayName="$(string.L_Alwaysmatchfiletype)">
            <value>
              <decimal value="2" />
            </value>
          </item>
        </enum>
      </elements>
    </policy>

Editor controls

<presentation id="L_Forcefileextenstionstomatch" xmlns="http://schemas.microsoft.com/GroupPolicy/2006/07/PolicyDefinitions">
        <dropdownList defaultItem="1" noSort="true" refId="L_Empty">
        </dropdownList>
      </presentation>

Supported platforms and category

excel16.Office.Microsoft.Policies.Windows:category:L_ExcelOptions
<category displayName="$(string.L_ExcelOptions)" name="L_ExcelOptions" xmlns="http://schemas.microsoft.com/GroupPolicy/2006/07/PolicyDefinitions">
      <parentCategory ref="excel16.Office.Microsoft.Policies.Windows:L_MicrosoftOfficeExcel" />
    </category>
excel16.Office.Microsoft.Policies.Windows:category:L_MicrosoftOfficeExcel
<category displayName="$(string.L_MicrosoftOfficeExcel)" name="L_MicrosoftOfficeExcel" xmlns="http://schemas.microsoft.com/GroupPolicy/2006/07/PolicyDefinitions" />
excel16.Office.Microsoft.Policies.Windows:category:L_Security
<category displayName="$(string.L_Security)" name="L_Security" xmlns="http://schemas.microsoft.com/GroupPolicy/2006/07/PolicyDefinitions">
      <parentCategory ref="excel16.Office.Microsoft.Policies.Windows:L_ExcelOptions" />
    </category>
excel16.Office.Microsoft.Policies.Windows:unresolved:Microsoft.Policies.Windows:SUPPORTED_Windows7
<unresolved reference="Microsoft.Policies.Windows:SUPPORTED_Windows7" />
excel16.Office.Microsoft.Policies.Windows:category:L_ExcelOptions
<category displayName="$(string.L_ExcelOptions)" name="L_ExcelOptions" xmlns="http://schemas.microsoft.com/GroupPolicy/2006/07/PolicyDefinitions">
      <parentCategory ref="excel16.Office.Microsoft.Policies.Windows:L_MicrosoftOfficeExcel" />
    </category>
<strings><string id="excel16.Office.Microsoft.Policies.Windows:L_ExcelOptions">Excel Options</string></strings>
excel16.Office.Microsoft.Policies.Windows:category:L_MicrosoftOfficeExcel
<category displayName="$(string.L_MicrosoftOfficeExcel)" name="L_MicrosoftOfficeExcel" xmlns="http://schemas.microsoft.com/GroupPolicy/2006/07/PolicyDefinitions" />
<strings><string id="excel16.Office.Microsoft.Policies.Windows:L_MicrosoftOfficeExcel">Microsoft Excel 2016</string></strings>
excel16.Office.Microsoft.Policies.Windows:category:L_Security
<category displayName="$(string.L_Security)" name="L_Security" xmlns="http://schemas.microsoft.com/GroupPolicy/2006/07/PolicyDefinitions">
      <parentCategory ref="excel16.Office.Microsoft.Policies.Windows:L_ExcelOptions" />
    </category>
<strings><string id="excel16.Office.Microsoft.Policies.Windows:L_Security">Security</string></strings>