Configure Exclusions by File Extension
Specifies file extensions to exclude from scanning. MSPs should configure sparingly to avoid security gaps. Document all exclusions.
- Policy path
- Computer Configuration > Administrative Templates > Windows Components > Microsoft Defender Antivirus > Exclusions
- Supported on
- Windows 10, Windows 11, Windows Server 2016 and later
Specifies file extensions to exclude from scanning. MSPs should configure sparingly to avoid security gaps. Document all exclusions. Security baselines recommend setting it to selective exclusions only.
Description
Configure Exclusions by File Extension is a Windows Group Policy setting located under Computer Configuration > Administrative Templates > Windows Components > Microsoft Defender Antivirus > Exclusions. It applies to the Computer Configuration branch and is classified as a Warning-level policy in the Microsoft Defender for Endpoint category.
Specifies file extensions to exclude from scanning. MSPs should configure sparingly to avoid security gaps. Document all exclusions.
Microsoft sets the default value to not set while industry security baselines (CIS, NIST, DISA STIG) recommend selective exclusions only.
Under the hood, this policy is enforced through the Windows registry at HKLM\Software\Policies\Microsoft\Windows Defender\Exclusions using the value name Extensions. 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 Microsoft Defender for Endpoint, 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 microsoft defender for endpoint on all domain-joined Windows endpoints.
- Roll out a CIS Benchmark-aligned baseline targeting 'Configure Exclusions by File Extension' 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 – Microsoft Defender for Endpoint) instead of editing Default Domain Policy.
- Navigate to
Computer Configuration > Administrative Templates > Windows Components > Microsoft Defender Antivirus > Exclusions. - Open Configure Exclusions by File Extension and set it to
selective exclusions only. - 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 Defender\Exclusions\Extensions. You can apply the same change with PowerShell:
New-Item -Path 'HKLM\Software\Policies\Microsoft\Windows Defender\Exclusions' -Force | Out-Null
Set-ItemProperty -Path 'HKLM\Software\Policies\Microsoft\Windows Defender\Exclusions' -Name 'Extensions' -Value <value> -Type DWordRegistry mapping
HKLM\Software\Policies\Microsoft\Windows Defender\ExclusionsExtensionsREG_SZselective exclusions onlynot set