Network Access: UNC Hardened Access (domain systems)
Restricts anonymous NULL session access to UNC paths. Setting to 1 requires authentication. Essential for MSPs blocking WMIEXEC and similar attacks.
- Policy path
- Computer Configuration > Windows Settings > Security Settings > Local Policies > Security Options
- Supported on
- Windows 10, Windows 11, Windows Server 2016 and later
Restricts anonymous NULL session access to UNC paths. Setting to 1 requires authentication. Essential for MSPs blocking WMIEXEC and similar attacks. Security baselines recommend setting it to 1.
Description
Network Access: UNC Hardened Access (domain systems) is a Windows Group Policy setting located under Computer Configuration > Windows Settings > Security Settings > Local Policies > Security Options. It applies to the Computer Configuration branch and is classified as a Warning-level policy in the SMB Hardening category.
Restricts anonymous NULL session access to UNC paths. Setting to 1 requires authentication. Essential for MSPs blocking WMIEXEC and similar attacks.
Microsoft sets the default value to 0 while industry security baselines (CIS, NIST, DISA STIG) recommend 1.
Under the hood, this policy is enforced through the Windows registry at HKLM\Software\Policies\Microsoft\Windows\NetworkAccess using the value name RestrictNullSessAccess. Modifying the value directly through regedit.exe or PowerShell produces the same effect as configuring the GPO, but going through Group Policy is preferred so that the setting is centrally managed and survives reboots, image rebuilds, and policy refresh cycles.
In-depth explanation
This setting has a meaningful impact on the security posture or operational stability of the system. Leaving it at the Microsoft default is acceptable for standalone or low-risk environments, but most security baselines (CIS, NIST, DISA STIG) explicitly call for hardening it before the device is exposed to untrusted users or networks.
The policy is grouped under SMB Hardening, which means it is typically applied through a domain-wide GPO linked at the OU level. In a multi-tenant MSP context, scope it through WMI filters or security group filtering rather than linking at the domain root, so that you can roll out progressively (pilot OU → wider rings → all production).
The setting takes effect after the next Group Policy refresh (gpupdate /force for immediate testing, or by default within ~90 minutes for workstations and ~5 minutes on domain controllers). For computer-side policies a reboot may be required; for user-side policies, a sign-off/sign-on cycle is enough.
Use cases
- Apply organization-wide hardening of smb hardening on all domain-joined Windows endpoints.
- Roll out a CIS Benchmark-aligned baseline targeting 'Network Access: UNC Hardened Access (domain systems)' via a dedicated GPO.
- Reduce attack surface for accounts that handle privileged credentials or sensitive data.
- Standardize the configuration across multiple customer tenants for an MSP-managed fleet.
Security implications
Leaving this policy at default does not directly grant an attacker access, but it widens the blast radius once initial access is obtained – passwords are easier to guess, lockout doesn't fire, audit trails are incomplete, or lateral movement is quieter. Most regulators and cyber-insurance underwriters now expect this control to be in place at least at the recommended level.
How to configure
- Open Group Policy Management Console (
gpmc.msc) on a domain controller or a workstation with RSAT installed. - Create or edit a GPO linked to the OU containing the target computer configurations. We recommend a dedicated baseline GPO (e.g. SEC – SMB Hardening) instead of editing Default Domain Policy.
- Navigate to
Computer Configuration > Windows Settings > Security Settings > Local Policies > Security Options. - Open Network Access: UNC Hardened Access (domain systems) and set it to
1. - Click OK and close the editor.
- On the target endpoint, run
gpupdate /force(or wait for the next refresh cycle), then verify withrsop.mscorgpresult /h report.html.
Direct registry path: HKLM\Software\Policies\Microsoft\Windows\NetworkAccess\RestrictNullSessAccess. You can apply the same change with PowerShell:
New-Item -Path 'HKLM\Software\Policies\Microsoft\Windows\NetworkAccess' -Force | Out-Null
Set-ItemProperty -Path 'HKLM\Software\Policies\Microsoft\Windows\NetworkAccess' -Name 'RestrictNullSessAccess' -Value <value> -Type DWordRegistry mapping
HKLM\Software\Policies\Microsoft\Windows\NetworkAccessRestrictNullSessAccessREG_DWORD10