ASR Rules in Windows 11: Configure and optimize security

In today's world, where Computer threats evolve at a dizzying pace, protecting our devices with robust systems has become a top priority. In this context, ASR Rules (Attack Surface Reduction Rules) en Windows 11 have emerged as one of the most effective strategies for protecting computers and networks against malware and attacks targeting common vulnerabilities. Whether you work in IT or are looking to improve the security of your personal or business devices, Knowing these rules in depth and how to apply them can make the difference against possible attacks..

We'll take a detailed look at what ASR Rules are, how to configure them from different platforms (Intune, Configuration Manager, Group Policy, and PowerShell), their advantages, limitations, and best practices. You'll also learn tuning and troubleshooting tips to help you get the most out of them, minimizing impacts on critical applications and streamlining the day-to-day operations of any IT department.

What are ASR Rules in Windows 11 and why are they so important?

The Attack Surface Reduction Rules (Attack Surface Reduction Rules) are a set of security regulations integrated into Microsoft Defender and manageable from Intune or other management tools. Its main objective is Avoid behaviors and actions that are commonly used by malware to compromise computers and networks: We're talking about blocking suspicious scripts, stopping potentially dangerous files from running, controlling macro usage in Office applications, and limiting credential theft attempts.

These rules not only shield access to common vulnerabilities, but also help reduce the risk of advanced attacks, ransomware, and other sophisticated threats.The best part is that they are highly customizable, allowing for flexible configurations to suit every environment, from large enterprises to individual users.

In Windows 11, ASR protection has reached new heights in granularity and manageability, marking a quantum leap from previous versions and becoming an essential part of any security strategy. ciberseguridad modern

Licensing and requirements in Windows 11

Before diving into the configuration and deployment of ASR Rules, it is necessary to understand key aspects about licenses and prerequisites. ASR Rules are available for Windows 10 and Windows 11 computers, although the full rules package can only be leveraged on enterprise editions (e.g., E3 or E5).. If you have a license Microsoft 365 E5, you'll have access to advanced monitoring and analytics capabilities from Defender for Endpoint or the Microsoft Defender XDR portal.

However, even with Windows Professional or Microsoft 365 E3 licenses, you can use ASR in a limited way.. The rules can be reviewed through the Event Viewer and your own monitoring systems can be developed. The important thing is to have Microsoft Defender Antivirus as a primary and active solution, since ASR rules rely on its analysis engine to evaluate suspicious behavior and block it.

Configuration methods: Intune, Configuration Manager, GPO, and PowerShell

One of the strengths of the ASR Rules lies in their versatility in managing and deploying policiesThere are several routes and tools, each suited to different environments and needs:

• IntuneIdeal for companies that manage device fleets via the cloud. It allows you to centrally configure and assign ASR policies, monitor their effectiveness, and apply adjustments or exclusions when necessary.
• Configuration Manager (SCCM): Advanced, traditional solution for large organizations. Allows you to create detailed policies and deploy them even in mixed or disconnected environments.
• Group Policy Objects (GPO): Perfect for environments with Active Directory, allowing you to define rules at the domain, organizational unit or specific computer level.
• PowerShell: Flexible option that allows you to configure, audit and even debug ASR Rules from the command line. commands, ideal for automation or advanced scripting.

Each method has its own advantages and considerations, but all Allows you to define the status of each ASR rule between: Block, Audit, Warning or DisabledThis provides absolute control over security behavior based on each organization's needs and risks.

Configuring ASR Rules with Intune

Intune has become the flagship solution for modern device management in enterprises, especially in Windows 11 environments.Configuring ASR Rules through this platform provides a centralized, scalable, and easy-to-monitor experience.

To begin, access the menu Endpoint Security in Intune and select Reduction of the surface area exposed to attacksYou can create a new policy or edit an existing one. Make sure you select the correct platform (Windows) and profile (ASR Rules).

Next, you can select the rules you want to apply:

• Block the execution of potentially obfuscated scripts
• Prevent Office applications from creating child processes (children)
• Prevent the use of Office macros to make Win32 API calls
• Block file execution from emails, webmails and devices USB that are not trustworthy
• Prevent credential theft and attacks on LSASS
• Control the use of JavaScript or VBScript in downloaded content
• Stop the abuse of vulnerable signed drivers

You can customize each rule to Block (active), Audit (only logs events), Warn (allows user to bypass blocking), or Disabled mode.Once the policy is configured, it is assigned to the relevant device groups.

Additionally, Intune allows Exclude files, paths, or applications that may be damaged by false alarms, adding even more flexibility.

Configuration from Microsoft Configuration Manager (SCCM)

Another widely used alternative is Configuration manager, especially in companies that still opt for local or hybrid management. The process consists of accessing Assets and Compliance → Endpoint Protection → Windows Defender Exploit Guard and create an Exploit Guard policy.

Within the wizard, the ASR rules to be activated are selected, either in mode Blocking or Auditing. Upon completion, the policy is distributed based on the device groups or collections defined in your enterprise environment.

Check frequently logs and reports generated by SCCM to ensure that rules are applied correctly and do not conflict with other security profiles.

Group Policy: Managing ASR through GPOs

The Group Policies They remain the preferred route in environments with Active Directory infrastructure. The general procedure is:

• Open the Group Policy Management Console (GPMC)
• Edit (or create) a new GPO and navigate to it Computer Configuration > Administrative Templates > Windows Components > Microsoft Defender Antivirus > Microsoft Defender Exploit Guard > Reducing the Attack Surface
• Enable settings Configure attack surface reduction rules
• Set the status of each rule by indicating its ID and the desired value: '1' for Block, '2' for Audit, '6' for Warn, '0' for Disable
• Optionally configure exclusions from the option Exclude files and paths from attack surface reduction rules

The control thus obtained is very detailed, but requires careful maintenance to avoid conflicts between policies at different levels.

PowerShell: Advanced Automation and Control

For advanced administrators or environments where automation is key, PowerShell offers the possibility of working with ASR Rules directly from the console or scripts. You can also consult the related aspects in What is secpol.msc and how can it help with security policy management?

Some examples of useful commands are:

• Enable an ASR rule:
• Set-MpPreference -AttackSurfaceReductionRules_Ids <ID_de_regla> -AttackSurfaceReductionRules_Actions Enabled
• Activate in Audit mode:
• Add-MpPreference -AttackSurfaceReductionRules_Ids <ID_de_regla> -AttackSurfaceReductionRules_Actions AuditMode
• Exclusions:
• Add-MpPreference -AttackSurfaceReductionOnlyExclusions "C:\Ruta\a\excluir"

This allows, for example, Automate the activation, auditing, and tuning of rules across large fleets of equipment, integrating tasks into CI/CD processes, deployment scripts, or even managing incidents in real time.

States available for each ASR Rule and how they work

Each individual ASR rule can be set to one of the following states, depending on what you are looking to achieve:

• Not configured / Disabled: The rule is not applied and related events are not logged.
• Block: The rule is activated and prohibited actions are directly blocked.
• Audit: Actions are allowed, but are logged for later review. Ideal for assessing the impact before enforcing the rule.
• Warn: The rule is applied, but the user receives an alert and can decide whether to continue.

This flexibility makes it easier Deploy rules first in Audit mode to monitor their impact, minimize disruptions, and then, after fine-tuning exclusions, switch to Full Blocking mode..

Main ASR rules in Windows 11 and their purpose

Among the many rules available, the following stand out for their effectiveness in preventing infections and unauthorized access:

• Block execution of potentially obfuscated scripts: Prevents the execution of suspicious scripts that are often used to load malware.
• Prevent Office from creating child processes: Prevents attacks where Office documents generate malware by launching other processes.
• Restrict Office macros that use Win32 API calls: especially protecting against exploits in malicious macros.
• Block execution of email and webmail files: Reduces your exposure to infected attachments or dangerous links in email.
• Prevent credential theft from LSASS: Protects credentials stored in memory and prevents attackers from moving laterally.
• Block content downloaded from untrusted USB drives: Minimizes malware risks on external devices.
• Prevent persistence by subscribing to WMI events: Stops persistence techniques used by advanced threats.
• Stop code injection into other processes: makes it difficult to evade other security controls.
• Protect against ransomware and encryption attacks: increasing the resilience of the system to this type of incident.

The full list may vary and grow as the Defender suite evolves, so it is recommended to consult it to identify new rules and their specific purpose..

Exclusions: How to ensure the operation of critical applications

One of the main challenges is balancing safety and operabilityThere are business applications that, due to their internal workings, may be blocked or generate false positives with certain ASR rules.

To EVITED these problems, You can define exclusions at the file, folder, or even specific application level.These exclusions can be managed:

• From the configuration panel in Intune, by importing CSV files, or by entering paths manually.
• Using the exclusions settings in SCCM or GPO, where the paths to be excluded are specified.
• Via PowerShell, with the command Add-MpPreference -AttackSurfaceReductionOnlyExclusions "<ruta>".

It is recommended that you analyze in Audit mode which applications generate events before applying blocks, so that you can fine-tune the exclusions and reduce the risk of blocking legitimate processes..

Policy conflicts and merging: how it works in corporate environments

In managed environments, it is common for a device to receive policies from multiple sources. ASR rules allow merging of policies, as long as there are no conflicts.If two policies define the same rule with different states, only the most restrictive setting will be applied, or in the event of a conflict, both will be invalid for that specific rule.

This behavior is designed to Avoid inconsistencies and ensure that environments maintain a minimum level of security, even if there is overlapping policiesTherefore, it is important to carefully plan the hierarchy and order of application of ASR policies within your organization.

Monitoring and analyzing ASR events in Windows 11

Monitoring the effectiveness of ASR Rules is just as important as their correct configuration. There are several tools and methods to check what's happening on your devices:

• Events viewer: Windows logs ASR-related events in Apps and services → Microsoft → Windows → Windows Defender → OperationalHere you can find detailed logs about triggered rules, blocks, and actions taken.
• PowerShell: You can check the active rules and their status on the computer using commands like Get-MPPreference | Select-Object -ExpandProperty AttackSurfaceReductionRules_Ids y Get-MPPreference | Select-Object -ExpandProperty AttackSurfaceReductionRules_Actions. In addition, you can consult information at
• MpCmdRun.exe: Running MpCmdRun.exe -getfiles You will generate a collection of logs and current configuration in a compressed file that you can inspect in depth.
• Microsoft Defender for Endpoints: If you have this solution, the section of Advanced Hunting allows you to use advanced queries to analyze events, affected files, and correlate suspicious activities on a large scale.

Continuous monitoring is vital to identify false positives, detect new threats, and adjust ASR settings without losing productivity..

Progressive deployment and adjustment: recommended best practices

Implementing ASR Rules safely and effectively involves following certain good practices that minimize risks:

• Always start in Audit modeThis way, you can identify in a controlled manner which applications would be blocked or affected by the rules, collecting events for at least 30 days.
• Review the impact of the rules in business applications, introducing exclusions as needed before entering Block mode.
• Periodically update your ASR configuration As Microsoft releases new rules or improves existing ones, ensuring protection against emerging threats.
• Document any exclusions and informs users about new security measures, requesting feedback on possible incidents.
• Use monitoring and reporting to dynamically adjust settings and correct possible malfunctions.

Related article:

secpol.msc: What it is and how to control the Local Security Policy in Windows

Isaac

Passionate writer about the world of bytes and technology in general. I love sharing my knowledge through writing, and that's what I'll do on this blog, show you all the most interesting things about gadgets, software, hardware, tech trends, and more. My goal is to help you navigate the digital world in a simple and entertaining way.