Overview of Attack Surface Reduction Rules in Intune

Prajwal Desai
Posted by Prajwal Desai
Overview of Attack Surface Reduction Rules in Intune

In this guide, we will learn about the Attack Surface Reduction Rules in Intune. Using Intune, you can create and configure ASR rules for your organization. Let’s examine what attack surface reduction rules are, as well as a list of the ASR configurable rules.

The Attack Surface reduction rules that you create in Intune (MEM) apply to Microsoft Defender for Endpoint Plan 2, Microsoft 365 Defender and Microsoft Defender Antivirus. There are many examples of ASR rules that you can create with Microsoft Intune and I will share a list of ASR Rules in this guide.

Microsoft recommends you to test how Intune ASR rules will impact your organization before enabling them by running ASR rules in audit mode for a brief period of time. While you are running the rules in audit mode, you can identify any line-of-business applications that might get blocked erroneously, and exclude them from ASR. Start with a small, controlled group to limit potential work disruptions, and later you can expand your deployment across your organization.

Attacks Surface Reduction is a complex topic, and there are many aspects to consider. To make it easier I am going to list some resources for getting started with Attack Surface Reduction rules in Intune.

What are Attack Surfaces?

Attack surfaces are all the places where your organization is vulnerable to cyberthreats and attacks. Defender for Endpoint includes numerous capabilities to help reduce your attack surfaces.

All the points where your company is exposed to cyberthreats and attacks are known as attack surfaces. Various features in Defender for Endpoint might help you decrease your attack surfaces.

Methods to Configure ASR Capabilities

When you configure attack surface reduction capabilities, you can choose from among several methods:

  • Microsoft Endpoint Manager (includes Microsoft Intune and Configuration Manager)
  • Group Policy
  • PowerShell cmdlets

What are Attack Surface Reduction Rules in Intune?

Attack surface reduction measures focus on actions that malware and malicious software commonly take to infect computers, such as: executable files and scripts used in Office applications or web mail that attempt to download or run files obfuscated. Another example is suspicious script behaviors that apps don’t usually initiate during normal day-to-day work.

For Intune, ASR rules target certain software behaviors, such as:

  • Launching executable files and scripts that attempt to download or run files
  • Running obfuscated or otherwise suspicious scripts
  • Behaviors that apps don’t usually occur during normal day-to-day work

By reducing the different attack surfaces, you can help prevent attacks from happening in the first place. Take a look at detailed guide on how to use attack surface reduction capabilities.

Operating System Requirements for ASR Rules

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

Licensing Requirements for ASR

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

Attack Surface Reduction Rules Deployment Phases

As with any new, large-scale implementation that could affect your line of business, it is important to plan and implement it in a methodical way. Because ASR rules are so good at stopping malware, they need to be carefully planned and set up to make sure they work best for your customers’ unique workflows. For ASR rules to work in your environment, you need to carefully plan, test, implement, and run them.

The below diagram illustrates four deployment phases of Attack Surface Reduction Rules.

  • Phase 1: Plan for ASR Rules
  • Phase 2: Test attack surface reduction (ASR) rules
  • Phase 3: Implement or Enable attack surface reduction (ASR) rules
  • Phase 4: Report and troubleshoot Microsoft Defender for Endpoint ASR Rules
Attack Surface Reduction Rules Deployment Phases
Attack Surface Reduction Rules Deployment Phases

List of Attack Surface Reduction Rules In Intune

With Intune, you can configure the following Attack Surface Reduction (ASR) rules and deploy it to your endpoints. The below table lists all the Intune ASR Rules, description and GUID that you can configure for your endpoints.

Intune ASR Rule NameASR Rule DescriptionRule GUID
Block abuse of exploited vulnerable signed driversThis rule prevents an application from writing a vulnerable signed driver to disk. The vulnerable signed drivers can be exploited by local applications – that have sufficient privileges – to gain access to the kernel eventually leading to system compromise.56a863a9-875e-4185-98a7-b882c64b5ce5
Block Adobe Reader from creating child processesThis rule prevents attacks by blocking Adobe Reader from creating processes.7674ba52-37eb-4a4f-a9a1-f0f9a1619a2c
Block all Office applications from creating child processesThis rule blocks Office apps from creating child processes. Office apps include Word, Excel, PowerPoint, OneNote, and Access.d4f940ab-401b-4efc-aadc-ad5f3c50688a
Block credential stealing from the Windows local security authority subsystem (lsass.exe)This ASR rule helps prevent credential stealing by locking down Local Security Authority Subsystem Service (LSASS). LSASS authenticates users who sign in on a Windows computer. Microsoft Defender Credential Guard in Windows normally prevents attempts to extract credentials from LSASS.9e6c4e1f-7d60-472f-ba1a-a39ef669e4b2
Block executable content from email client and webmailThis rule blocks the following file types from launching from email opened within the Microsoft Outlook application, or Outlook.com and other popular webmail providersbe9ba2d9-53ea-4cdc-84e5-9b1eeee46550
Block executable files from running unless they meet a prevalence, age, or trusted list criterionThis ASR rule blocks executable files, such as .exe, .dll, or .scr, from launching. Thus, launching untrusted or unknown executable files can be risky, as it might not be initially clear if the files are malicious.01443614-cd74-433a-b99e-2ecdc07bfc25
Block execution of potentially obfuscated scriptsThis rule detects suspicious properties within an obfuscated script. Malware writers and developers of legitimate software frequently employ script obfuscation to conceal intellectual property or speed up the loading of scripts. In order to make malicious code more difficult to comprehend and prevent it from being closely examined by security tools and humans, malware developers also employ obfuscation.5beb7efe-fd9a-4556-801d-275e5ffc04cc
Block JavaScript or VBScript from launching downloaded executable contentThis ASR rule prevents scripts from launching potentially malicious downloaded content. Malware written in JavaScript or VBScript often acts as a downloader to fetch and launch other malware from the Internet.d3e037e1-3eb8-44c8-a917-57927947596d
Block Office applications from creating executable contentThis rule prevents Office apps, including Word, Excel, and PowerPoint, from creating potentially malicious executable content, by blocking malicious code from being written to disk.3b576869-a4ec-4529-8536-b80a7769e899
Block Office applications from injecting code into other processesThis rule blocks code injection attempts from Office apps into other processes. Attackers might attempt to use Office apps to migrate malicious code into other processes through code injection, so the code can masquerade as a clean process.75668c1f-73b5-4cf0-bb93-3ecf5cb7cc84
Block Office communication application from creating child processesThis rule prevents Outlook from creating child processes, while still allowing legitimate Outlook functions.26190899-1602-49e8-8b27-eb1d0a1ce869
Block persistence through WMI event subscription
* File and folder exclusions not supported.
This rule prevents malware from abusing WMI to attain persistence on a device.e6db77e5-3df2-4cf1-b95a-636979351e5b
Block process creations originating from PSExec and WMI commandsThis ASR rule blocks processes created through PsExec and WMI from running. Both PsExec and WMI can remotely execute code. There’s a risk of malware abusing functionality of PsExec and WMI for command and control purposes, or to spread an infection throughout an organization’s network.d1e49aac-8f56-4280-b9ba-993a6d77406c
Block untrusted and unsigned processes that run from USBWith this rule, admins can prevent unsigned or untrusted executable files from running from USB removable drives, including SD cards. Blocked file types include executable files (such as .exe, .dll, or .scr)b2b3f03d-6a65-4f7b-a9c7-1c7ef74a9ba4
Block Win32 API calls from Office macrosThis rule prevents VBA macros from calling Win32 APIs.92e97fa1-2edf-4476-bdd6-9dd0b4dddc7b
Use advanced protection against ransomwareThis rule provides an extra layer of protection against ransomware. It uses both client and cloud heuristics to determine whether a file resembles ransomware.c1db55ab-c21a-4637-bb3f-a12568109d35
List of Intune ASR Rules

Create Attack Surface Reduction Rule in Intune

The process of creating a new ASR rule in Intune involves following steps:

Create Attack Surface Reduction Rule in Intune
Create Attack Surface Reduction Rule in Intune

On Create a profile window, you have two options for choosing the platform.

  • Windows 10 and later
  • Windows 10 and later (ConfigMgr)

Select the platform as Windows 10 and later.

Attack Surface Reduction Rules in Intune - Select Platform
Attack Surface Reduction Rules in Intune – Select Platform

For the profile, select Attack surface reduction rules and click Create.

Attack Surface Reduction Rules in Intune
Attack Surface Reduction Rules in Intune

Configure ASR Rules using MEM | Intune

You can use Microsoft Endpoint Manager (MEM | Intune) Endpoint Security to configure custom ASR rules with following steps.

1. On the Create Profile page, click the Basics tab and enter the Profile name and description for the Attack Surface Reduction rule that you are going to configure. Click Next.

Configure ASR Rules using MEM | Intune
Configure ASR Rules using MEM | Intune

2. On the Configuration Settings tab, you’ll find a list of ASR rules that you can configure. Every ASR rule has got 4 modes that you can choose from:

  • Not configured or Disable: The state in which the ASR rule hasn’t been enabled or has been disabled. The code for this state = 0.
  • Block: The state in which the ASR rule is enabled. The code for this state is 1.
  • Audit: The state in which the ASR rule is evaluated for the effect it would have on the organization or environment if enabled (set to block or warn). The code for this state is 2.
  • Warn: The state in which the ASR rule is enabled and presents a notification to the end-user, but permits the end-user to bypass the block. The code for this state is 6.

In the Configuration settings tab, under Attack Surface Reduction Rules, set all rules to Audit mode. When you initially configure a new ASR rule in Intune, it is recommended that you test it with the Audit mode. Testing attack surface reduction (ASR) rules helps you determine if rules will impede line-of-business operations prior to enabling any rule.

Configure ASR Rules using MEM | Intune
Configure ASR Rules using MEM | Intune

In the next steps, select the Scope Tags where you can add tag information to specific devices. On the Assignments tab, you can “deploy” or “assign” the profile to your user or device groups. Review your settings in the Review + create pane. Click Create to apply the rules.

Finally, your new attack surface reduction policy for ASR rules is listed in Endpoint security | Attack surface reduction. You can select the ASR rule and make any modifications if required.

View Attack Surface Reduction Rules in Intune
View Attack Surface Reduction Rules in Intune

Test and Troubleshoot your Attack Surface Reduction rules

After you’ve fully deployed attack surface reduction (ASR) rules with Intune, you must have processes in place to monitor, troubleshoot and respond to ASR-related activities.

There are two ways to analyze the ADR rules and reporting details:

  • Understand the Attack surface reduction rules reporting page in the Microsoft 365 Defender portal: Get a detailed report with ASR rules events, blocks, and warnings if you have an E5 subscription and use Microsoft Defender for Endpoint.
  • Use Windows Event Viewer: To review apps that would have been blocked, launch Event Viewer and filter for Event ID 1121 in the Microsoft-Windows-Windows Defender/Operational log. The following table lists all network protection events that you can use for ASR troubleshooting.
Event IDDescription
5007Event when settings are changed
1121Event when an attack surface reduction rule fires in block mode
1122Event when an attack surface reduction rule fires in audit mode

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Prajwal Desai
Posted by Prajwal Desai
Prajwal Desai is a Microsoft MVP in Intune and SCCM. He writes articles on SCCM, Intune, Windows 365, Windows Server, Windows 11, WordPress and other topics, with the goal of providing people with useful information.