Customize attack surface reduction rules
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Attack surface reduction rules help prevent software behaviors that are often abused to compromise your device or network. For example, an attacker might try to run an unsigned script off of a USB drive, or have a macro in an Office document make calls directly to the Win32 API. Attack surface reduction rules can constrain these kinds of risky behaviors and improve your organization's defensive posture.
You can set attack surface reduction rules for devices running any of the following editions and versions of Windows:
- Windows 10 Pro, version 1709 or later
- Windows 10 Enterprise, version 1709 or later
- Windows Server, version 1803 (Semi-Annual Channel) or later
- Windows Server 2019
You can use Group Policy, PowerShell, and Mobile Device Management (MDM) configuration service providers (CSP) to configure these settings.
See Requirements in the "Enable attack surface reduction rules" article for information about supported operating systems and additional requirement information.
Exclude files and folders
You can choose to exclude files and folders from being evaluated by attack surface reduction rules. When excluded, the file won't be blocked from running even if an attack surface reduction rule detects that the file contains malicious behavior.
For example, consider the ransomware rule:
The ransomware rule is designed to help enterprise customers reduce risks of ransomware attacks while ensuring business continuity. By default, the ransomware rule errors on the side of caution and protect against files that haven't yet attained sufficient reputation and trust. To reemphasize, the ransomware rule only triggers on files that have not gained enough positive reputation and prevalence, based on usage metrics of millions of our customers. Usually, the blocks are self resolved, because each file's "reputation and trust" values are incrementally upgraded as non-problematic usage increases.
In cases in which blocks aren't self resolved in a timely manner, customers can - at their own risk - make use of either the self-service mechanism or an Indicator of Compromise (IOC)-based "allow list" capability to unblock the files themselves.
Excluding or unblocking files or folders could potentially allow unsafe files to run and infect your devices. Excluding files or folders can severely reduce the protection provided by attack surface reduction rules. Files that would have been blocked by a rule will be allowed to run, and there will be no report or event recorded.
An exclusion applies to all rules that allow exclusions. You can specify an individual file, folder path, or the fully qualified domain name for a resource. However, you cannot limit an exclusion to a specific 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 will continue to trigger events until the service is stopped and restarted.
Attack surface reduction supports environment variables and wildcards. For information about using wildcards, see use wildcards in the file name and folder path or extension exclusion lists . If you are encountering problems with rules detecting files that you believe should not be detected, use audit mode to test the rule.
|Block abuse of exploited vulnerable signed drivers||
|Block Adobe Reader from creating child processes||
|Block all Office applications from creating child processes||
|Block credential stealing from the Windows local security authority subsystem (lsass.exe)||
|Block executable content from email client and webmail||
|Block executable files from running unless they meet a prevalence, age, or trusted list criteria||
|Block execution of potentially obfuscated scripts||
|Block Office applications from creating executable content||
|Block Office applications from injecting code into other processes||
|Block Office communication applications from creating child processes||
|Block persistence through WMI event subscription||
|Block process creations originating from PSExec and WMI commands||
|Block untrusted and unsigned processes that run from USB||
|Block Win32 API calls from Office macro||
|Use advanced protection against ransomware||
See the attack surface reduction topic for details on each rule.
Use Group Policy to exclude files and folders
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.
In the Group Policy Management Editor, go to Computer configuration and click Administrative templates.
Expand the tree to Windows components > Microsoft Defender Antivirus > Microsoft Defender Exploit Guard > Attack surface reduction.
Double-click 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.
Do not use quotes as they are not supported for either the Value name column or the Value column.
Use PowerShell to exclude files and folders
Type powershell in the Start menu, right-click Windows PowerShell and select Run as administrator
Enter the following cmdlet:
Add-MpPreference -AttackSurfaceReductionOnlyExclusions "<fully qualified path or resource>"
Continue to use
Add-MpPreference -AttackSurfaceReductionOnlyExclusions to add more folders to the list.
Add-MpPreference to append or add apps to the list. Using the
Set-MpPreference cmdlet will overwrite the existing list.
Use MDM CSPs to exclude files and folders
Use the ./Vendor/MSFT/Policy/Config/Defender/AttackSurfaceReductionOnlyExclusions configuration service provider (CSP) to add exclusions.
Customize the notification
You can customize the notification for when a rule is triggered and blocks an app or file. See the Windows Security article.