Control mounting ReFS volumes on USB and IEEE 1394 disks: registry value RefsExternalBusMountPolicyComputerHKLM\System\CurrentControlSet\Policies

Policy ID: BlockExternalBusMount
Scope: Computer Configuration
Supported on: At least Windows 11 Version 22H2
Source: Administrative Templates (.admx) for Windows 11 2026 Update (26H2) (version 1.0)
Category: System › Filesystem

Registry

RefsExternalBusMountPolicy

REG_DWORDComputer

HKLM\System\CurrentControlSet\Policies Current key

Enabled value: Depends on the option value
Element: Action for ReFS volumes on USB or IEEE 1394 disks

Options
Item	Stored value
Off	0
Audit only	1
Block	2

Apply with .reg · CMD · PowerShell

.reg

Windows Registry Editor Version 5.00

[HKEY_LOCAL_MACHINE\System\CurrentControlSet\Policies]

; Options (use only one)
; Off
"RefsExternalBusMountPolicy"=dword:00000000
; Audit only
"RefsExternalBusMountPolicy"=dword:00000001
; Block
"RefsExternalBusMountPolicy"=dword:00000002

CMD

:: Options (use only one)

:: Off
reg add "HKLM\System\CurrentControlSet\Policies" /v "RefsExternalBusMountPolicy" /t REG_DWORD /d 0 /f
:: Audit only
reg add "HKLM\System\CurrentControlSet\Policies" /v "RefsExternalBusMountPolicy" /t REG_DWORD /d 1 /f
:: Block
reg add "HKLM\System\CurrentControlSet\Policies" /v "RefsExternalBusMountPolicy" /t REG_DWORD /d 2 /f

PowerShell

# Common: create the key
New-Item -Path 'HKLM:\System\CurrentControlSet\Policies' -Force | Out-Null

# Options (use only one)
# Off
New-ItemProperty -Path 'HKLM:\System\CurrentControlSet\Policies' -Name 'RefsExternalBusMountPolicy' -PropertyType DWord -Value 0 -Force | Out-Null
# Audit only
New-ItemProperty -Path 'HKLM:\System\CurrentControlSet\Policies' -Name 'RefsExternalBusMountPolicy' -PropertyType DWord -Value 1 -Force | Out-Null
# Block
New-ItemProperty -Path 'HKLM:\System\CurrentControlSet\Policies' -Name 'RefsExternalBusMountPolicy' -PropertyType DWord -Value 2 -Force | Out-Null