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Enable attack surface reduction rules

  • Article

Applies to:

Platforms

  • Windows

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Attack surface reduction rules help prevent actions that malware often abuses to compromise devices and networks.

Requirements

Attack surface reduction features across Windows versions

You can set attack surface reduction rules for devices that are running any of the following editions and versions of Windows:

To use the entire feature-set of attack surface reduction rules, you need:

  • Microsoft Defender Antivirus as primary AV (real-time protection on)
  • Cloud-Delivery Protection on (some rules require that)
  • Windows 10 Enterprise E5 or E3 License

Although attack surface reduction rules don't require a Windows E5 license, with a Windows E5 license, you get advanced management capabilities including monitoring, analytics, and workflows available in Defender for Endpoint, as well as reporting and configuration capabilities in the Microsoft Defender XDR portal. These advanced capabilities aren't available with an E3 license, but you can still use Event Viewer to review attack surface reduction rule events.

Each attack surface reduction rule contains one of four settings:

  • Not configured | Disabled: Disable the attack surface reduction rule
  • Block: Enable the attack surface reduction rule
  • Audit: Evaluate how the attack surface reduction rule would impact your organization if enabled
  • Warn: Enable the attack surface reduction rule but allow the end user to bypass the block

We recommend using attack surface reduction rules with a Windows E5 license (or similar licensing SKU) to take advantage of the advanced monitoring and reporting capabilities available in Microsoft Defender for Endpoint (Defender for Endpoint). However, if you have another license, such as Windows Professional or Windows E3 that doesn't include advanced monitoring and reporting capabilities, you can develop your own monitoring and reporting tools on top of the events that are generated at each endpoint when attack surface reduction rules are triggered (for example, Event Forwarding).

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To learn more about Windows licensing, see Windows 10 Licensing and get the Volume Licensing guide for Windows 10.

You can enable attack surface reduction rules by using any of these methods:

Enterprise-level management such as Intune or Microsoft Configuration Manager is recommended. Enterprise-level management overwrites any conflicting Group Policy or PowerShell settings on startup.

Exclude files and folders from attack surface reduction rules

You can exclude files and folders from being evaluated by most attack surface reduction rules. This means that even if an attack surface reduction rule determines the file or folder contains malicious behavior, it doesn't block the file from running.

Important

Excluding files or folders can severely reduce the protection provided by attack surface reduction rules. Excluded files will be allowed to run, and no report or event will be recorded. If attack surface reduction rules are detecting files that you believe shouldn't be detected, you should use audit mode first to test the rule. An exclusion is applied only when the excluded application or service starts. For example, if you add an exclusion for an update service that is already running, the update service continues to trigger events until the service is stopped and restarted.

When adding exclusions, keep these points in mind:

Policy Conflict

  1. If a conflicting policy is applied via MDM and GP, the setting applied from GP takes precedence.

  2. Attack surface reduction rules for managed devices now support behavior for merger of settings from different policies, to create a superset of policy for each device. Only the settings that aren't in conflict are merged, while those that are in conflict aren't added to the superset of rules. Previously, if two policies included conflicts for a single setting, both policies were flagged as being in conflict, and no settings from either profile would be deployed. Attack surface reduction rule merge behavior is as follows:

    • Attack surface reduction rules from the following profiles are evaluated for each device to which the rules apply:
    • Settings that don't have conflicts are added to a superset of policy for the device.
    • When two or more policies have conflicting settings, the conflicting settings aren't added to the combined policy, while settings that don't conflict are added to the superset policy that applies to a device.
    • Only the configurations for conflicting settings are held back.

Configuration methods

This section provides configuration details for the following configuration methods:

The following procedures for enabling attack surface reduction rules include instructions for how to exclude files and folders.

Intune

Device Configuration Profiles

  1. Select Device configuration > Profiles. Choose an existing endpoint protection profile or create a new one. To create a new one, select Create profile and enter information for this profile. For Profile type, select Endpoint protection. If you've chosen an existing profile, select Properties and then select Settings.

  2. In the Endpoint protection pane, select Windows Defender Exploit Guard, then select Attack Surface Reduction. Select the desired setting for each attack surface reduction rule.

  3. Under Attack Surface Reduction exceptions, enter individual files and folders. You can also select Import to import a CSV file that contains files and folders to exclude from attack surface reduction rules. Each line in the CSV file should be formatted as follows:

    C:\folder, %ProgramFiles%\folder\file, C:\path

  4. Select OK on the three configuration panes. Then select Create if you're creating a new endpoint protection file or Save if you're editing an existing one.

Endpoint security policy

  1. Select Endpoint Security > Attack surface reduction. Choose an existing attack surface reduction rule or create a new one. To create a new one, select Create Policy and enter information for this profile. For Profile type, select Attack surface reduction rules. If you've chosen an existing profile, select Properties and then select Settings.

  2. In the Configuration settings pane, select Attack Surface Reduction and then select the desired setting for each attack surface reduction rule.

  3. Under List of additional folders that need to be protected, List of apps that have access to protected folders, and Exclude files and paths from attack surface reduction rules, enter individual files and folders. You can also select Import to import a CSV file that contains files and folders to exclude from attack surface reduction rules. Each line in the CSV file should be formatted as follows:

    C:\folder, %ProgramFiles%\folder\file, C:\path

  4. Select Next on the three configuration panes, then select Create if you're creating a new policy or Save if you're editing an existing policy.

Custom profile in Intune

You can use Microsoft Intune OMA-URI to configure custom attack surface reduction rules. The following procedure uses the rule Block abuse of exploited vulnerable signed drivers for the example.

  1. Open the Microsoft Intune admin center. In the Home menu, click Devices, select Configuration profiles, and then click Create profile.

    The Create profile page in the Microsoft Intune admin center portal.

  2. In Create a profile, in the following two drop-down lists, select the following:

    • In Platform, select Windows 10 and later
    • In Profile type, select Templates
    • If attack surface reduction rules are already set through Endpoint security, in Profile type, select Settings Catalog.

    Select Custom, and then select Create.

    The rule profile attributes in the Microsoft Intune admin center portal.

  3. The Custom template tool opens to step 1 Basics. In 1 Basics, in Name, type a name for your template, and in Description you can type a description (optional).

    The basic attributes in the Microsoft Intune admin center portal

  4. Click Next. Step 2 Configuration settings opens. For OMA-URI Settings, click Add. Two options now appear: Add and Export.

    The configuration settings in the Microsoft Intune admin center portal.

  5. Click Add again. The Add Row OMA-URI Settings opens. In Add Row, do the following:

    • In Name, type a name for the rule.

    • In Description, type a brief description.

    • In OMA-URI, type or paste the specific OMA-URI link for the rule that you're adding. Refer to the MDM section in this article for the OMA-URI to use for this example rule. For attack surface reduction rule GUIDS, see Per rule descriptions in the article: Attack surface reduction rules.

    • In Data type, select String.

    • In Value, type or paste the GUID value, the = sign and the State value with no spaces (GUID=StateValue). Where:

      • 0: Disable (Disable the attack surface reduction rule)
      • 1: Block (Enable the attack surface reduction rule)
      • 2: Audit (Evaluate how the attack surface reduction rule would impact your organization if enabled)
      • 6: Warn (Enable the attack surface reduction rule but allow the end-user to bypass the block)

    The OMA URI configuration in the Microsoft Intune admin center portal

  6. Select Save. Add Row closes. In Custom, select Next. In step 3 Scope tags, scope tags are optional. Do one of the following:

    • Select Select Scope tags, select the scope tag (optional) and then select Next.
    • Or select Next

  7. In step 4 Assignments, in Included Groups, for the groups that you want this rule to apply, select from the following options:

    • Add groups
    • Add all users
    • Add all devices

    The assignments in the Microsoft Intune admin center portal

  8. In Excluded groups, select any groups that you want to exclude from this rule, and then select Next.

  9. In step 5 Applicability Rules for the following settings, do the following:

    • In Rule, select either Assign profile if, or Don't assign profile if

    • In Property, select the property to which you want this rule to apply

    • In Value, enter the applicable value or value range

    The applicability rules in the Microsoft Intune admin center portal

  10. Select Next. In step 6 Review + create, review the settings and information you've selected and entered, and then select Create.

    The Review and create option in the Microsoft Intune admin center portal

    Rules are active and live within minutes.

Note

Conflict handling:

If you assign a device two different attack surface reduction policies, potential policy conflicts can occur, depending on whether rules are assigned different states, whether conflict management is in place, and whether the result is an error. Nonconflicting rules do not result in an error, and such rules are applied correctly. The first rule is applied, and subsequent nonconflicting rules are merged into the policy.

MDM

Use the ./Vendor/MSFT/Policy/Config/Defender/AttackSurfaceReductionRules configuration service provider (CSP) to individually enable and set the mode for each rule.

The following is a sample for reference, using GUID values for Attack surface reduction rules reference.

OMA-URI path: ./Vendor/MSFT/Policy/Config/Defender/AttackSurfaceReductionRules

Value: 75668c1f-73b5-4cf0-bb93-3ecf5cb7cc84=2|3b576869-a4ec-4529-8536-b80a7769e899=1|d4f940ab-401b-4efc-aadc-ad5f3c50688a=2|d3e037e1-3eb8-44c8-a917-57927947596d=1|5beb7efe-fd9a-4556-801d-275e5ffc04cc=0|be9ba2d9-53ea-4cdc-84e5-9b1eeee46550=1

The values to enable (Block), disable, warn, or enable in audit mode are:

  • 0: Disable (Disable the attack surface reduction rule)
  • 1: Block (Enable the attack surface reduction rule)
  • 2: Audit (Evaluate how the attack surface reduction rule would impact your organization if enabled)
  • 6: Warn (Enable the attack surface reduction rule but allow the end-user to bypass the block). Warn mode is available for most of the attack surface reduction rules.

Use the ./Vendor/MSFT/Policy/Config/Defender/AttackSurfaceReductionOnlyExclusions configuration service provider (CSP) to add exclusions.

Example:

OMA-URI path: ./Vendor/MSFT/Policy/Config/Defender/AttackSurfaceReductionOnlyExclusions

Value: c:\path|e:\path|c:\Exclusions.exe

Note

Be sure to enter OMA-URI values without spaces.

Microsoft Configuration Manager

  1. In Microsoft Configuration Manager, go to Assets and Compliance > Endpoint Protection > Windows Defender Exploit Guard.

  2. Select Home > Create Exploit Guard Policy.

  3. Enter a name and a description, select Attack Surface Reduction, and select Next.

  4. Choose which rules will block or audit actions and select Next.

  5. Review the settings and select Next to create the policy.

  6. After the policy is created, select Close.

Warning

There is a known issue with the applicability of Attack Surface Reduction on Server OS versions which is marked as compliant without any actual enforcement. Currently, there is no ETA for when this will be fixed.

Group Policy

Warning

If you manage your computers and devices with Intune, Configuration Manager, or other enterprise-level management platform, the management software will overwrite any conflicting Group Policy settings on startup.

  1. On your Group Policy management computer, open the Group Policy Management Console, right-click the Group Policy Object you want to configure and select Edit.

  2. In the Group Policy Management Editor, go to Computer configuration and select Administrative templates.

  3. Expand the tree to Windows components > Microsoft Defender Antivirus > Microsoft Defender Exploit Guard > Attack surface reduction.

  4. Select Configure Attack surface reduction rules and select Enabled. You can then set the individual state for each rule in the options section. Select Show... and enter the rule ID in the Value name column and your chosen state in the Value column as follows:

    • 0: Disable (Disable the attack surface reduction rule)

    • 1: Block (Enable the attack surface reduction rule)

    • 2: Audit (Evaluate how the attack surface reduction rule would impact your organization if enabled)

    • 6: Warn (Enable the attack surface reduction rule but allow the end-user to bypass the block)

      attack surface reduction rules in Group Policy

  5. To exclude files and folders from attack surface reduction rules, select the Exclude files and paths from Attack surface reduction rules setting and set the option to Enabled. Select Show and enter each file or folder in the Value name column. Enter 0 in the Value column for each item.

    Warning

    Do not use quotes as they are not supported for either the Value name column or the Value column. The rule ID should not have any leading or trailing spaces.

PowerShell

Warning

If you manage your computers and devices with Intune, Configuration Manager, or another enterprise-level management platform, the management software overwrites any conflicting PowerShell settings on startup.

  1. Type powershell in the Start menu, right-click Windows PowerShell and select Run as administrator.

  2. Type one of the following cmdlets. (For more information, such as rule ID, refer to Attack surface reduction rules reference.)

    Task PowerShell cmdlet
    Enable attack surface reduction rules Set-MpPreference -AttackSurfaceReductionRules_Ids <rule ID> -AttackSurfaceReductionRules_Actions Enabled
    Enable attack surface reduction rules in audit mode Add-MpPreference -AttackSurfaceReductionRules_Ids <rule ID> -AttackSurfaceReductionRules_Actions AuditMode
    Enable attack surface reduction rules in warn mode Add-MpPreference -AttackSurfaceReductionRules_Ids <rule ID> -AttackSurfaceReductionRules_Actions Warn
    Enable attack surface reduction Block abuse of exploited vulnerable signed drivers Add-MpPreference -AttackSurfaceReductionRules_Ids 56a863a9-875e-4185-98a7-b882c64b5ce5 -AttackSurfaceReductionRules_Actions Enabled
    Turn off attack surface reduction rules Add-MpPreference -AttackSurfaceReductionRules_Ids <rule ID> -AttackSurfaceReductionRules_Actions Disabled

    Important

    You must specify the state individually for each rule, but you can combine rules and states in a comma-separated list.

    In the following example, the first two rules are enabled, the third rule is disabled, and the fourth rule is enabled in audit mode: Set-MpPreference -AttackSurfaceReductionRules_Ids <rule ID 1>,<rule ID 2>,<rule ID 3>,<rule ID 4> -AttackSurfaceReductionRules_Actions Enabled, Enabled, Disabled, AuditMode

    You can also use the Add-MpPreference PowerShell verb to add new rules to the existing list.

    Warning

    Set-MpPreference overwrites the existing set of rules. If you want to add to the existing set, use Add-MpPreference instead. You can obtain a list of rules and their current state by using Get-MpPreference.

  3. To exclude files and folders from attack surface reduction rules, use the following cmdlet:

    Add-MpPreference -AttackSurfaceReductionOnlyExclusions "<fully qualified path or resource>"

    Continue to use Add-MpPreference -AttackSurfaceReductionOnlyExclusions to add more files and folders to the list.

    Important

    Use Add-MpPreference to append or add apps to the list. Using the Set-MpPreference cmdlet will overwrite the existing list.

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