The Magnificent ASR Rules

The Magnificent ASR Rules

This blog is the third part of the Endpoint Security Series. It will be about the Attack Surface Reduction (ASR) Rules.

I will devide this blog into multiple part

  1. ASR Explained
  2. Background Information about ASR
  3. Testing/Monitoring it
  4. How to deploy ASR rules on the go?
  5. Troubleshooting

1.ASR Explained

Windows Defender is one of the key pillars within Microsoft’s security products. Windows defender is enabled out of the box when deploying Windows 10. But only relying on the basic/default configuration is not best practice.

As mentioned in my last blog, it’s very important to harden your Office apps.

A perfect addition is “Attack Surface Reduction” (ASR). ASR can be configured by setting the ASR rules in the device endpoint manager. By default, they’re not configured, so you’re not protected against more sophisticated attacks!! These ASR rules can be configured by creating an endpoint protection device configuration or by creating a new attack surface reduction policy within the endpoint security settings.

There are many rules you can configure

If you want to know more about each rule, please visit this Microsoft page

Use attack surface reduction rules to prevent malware infection | Microsoft Docs

2.Background information about ASR

-The ASR rules can be: on/not configured or audit mode (it’s best practice to make sure you audit first before you enable them)

-You can configure them with PowerShell: Set-MPPreference -AttackSurfaceReductionRules_Ids

Exclusions will affect every ASR rule. But not all ASR rules support exclusions. Two of them do not support exclusions:

-Only enable the ASR rule: “block process creations originating from PSExec and WMI commands” when you are using Intune or another MDM solution! Management through Microsoft Endpoint Configuration Manager (MECM) will stop functioning because this rule blocks WMI commands.

-Cloud delivered protection has to be enabled as a requirement for the rule: “Block executable files from running unless they meet a prevalence, age, or trusted list criterion”. Admins can’t specify anything with this rule, because it’s owned by Microsoft.

-A Windows 10 Pro/Enterprise/Education license is required

-ASR rules configured in Intune do support wildcard and environmental variables exclusions. Beware, ASR rules don’t support user context exclusions, as they’re running in system context. Also, it’s very nice that some exclusions are already built-in.

– Windows event log is the key when you want to wisely audit the ASR rules first.

-Check the registry when you deployed the ASR rules. Every GUID corresponds to an ASR rule.

3. Testing/Monitoring ASR

If you want to test your ASR deployment, you will need to visit this page to download some nice DOCX you can play with

https://demo.wd.microsoft.com/?ocid=cx-wddocs-testground

-Do you fancy reports as well? Go check out the ASR reports after you tested on the Microsoft playground. You will find it in the security.microsoft.com portal.

Regels voor het verminderen van kwetsbaarheid voor aanvallen – Microsoft 365-beveiliging

And if you want to do some advanced hunting

Advanced hunting – Microsoft Defender for Endpoint (windows.com)

And Enter this query: DeviceEvents| where ActionType startswith ‘Asr’

4. How to deploy ASR rules on the go?

As mentioned at the beginning of this blog, you can do so by creating a new Endpoint Security configuration Profile

But why not doing it with PowerShell?

Just download this zip file. It contains a JSON file and a PowerShell Script. 

https://call4cloud.nl/wp-content/uploads/2020/07/Windows10_asr.zip

The JSON file contains all ASR settings, you can modify these according to your business needs. Afterwards, just launch the PowerShell script to deploy the settings.

Open Intune device configurations to notice a new device configuration policy has just been created.

5. Troubleshooting

Deploying it and making it work is great but what are you going to do when all systems fail?

You will need to have some good understanding how ASR works and where the events are logged.

I created a really good blog on how to determine if ASR is blocking even when the event log tells you nothing

Conclusion

Not setting the ASR rules when you have the proper licensing for it, could be a mistake… ASR rules are a very successful way to block more sophisticated attacks. But of course, ASR rules are just another barrier that can be bypassed. I’ll tell you more in my next blog…

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If you want to read more parts of the Endpoint Security Series:

*The second part about CFA (click here)

*The Fourth Part about WDAC (click here)

3 thoughts on “The Magnificent ASR Rules

  1. Pingback: The forgotten fruits of securing your Windows 10 Endpoint - Call4Cloud
  2. What about deploying ASR using Intune ATP security baseline? according to Microsoft baselines are the recommended configuration in terms of security posture, or am I missing something?
    The only thing that’s isn’t include within is WDATP tamper protection (which is wired).

    1. Hi

      Of course, that is a good option. But I prefer to work with standalone configurations. When enabling the atp baseline, options like hello/firewall/device installation/bitlocker are enabled by default. I have got 1 device configuration profile for BitLocker, 1 profile for hello etc. I find it easier to troubleshoot instead of 1 profile with all settings defined.

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