Security baseline (DRAFT): Windows 10 and Windows Server, version 20H2

This post has been republished via RSS; it originally appeared at: New blog articles in Microsoft Tech Community.

The proposed draft of the Windows 10 and Windows Server, version 20H2 (aka the October 2020 Update) security baseline is now available for download!

We invite you to download the draft baseline package (attached to this post), evaluate the proposed baselines, and provide us your comments and feedback below.

Windows 10 and Windows Server, version 20H2 bring very few new policy settings. All new settings are listed in the accompanying documentation. At this point, none of  the new policy settings meet the criteria for inclusion in the security baseline; however, there are a few existing policies we plan to change, and these are highlighted below along with our recommendations.

Block at first sight

We started the journey for cloud protection several years ago. Based on our analysis of the security value versus the cost of implementation, we feel it is time to add the Microsoft Defender Antivirus block at first sight feature to the security baseline. Block at first sight was first introduced in Windows 10, version 1607 and allows new malware to be detected and blocked within seconds by leveraging various machine learning techniques and the power of the Microsoft cloud.

Block at first sight currently requires six settings to be configured. Our baseline already sets two of them, Join Microsoft MAPS and Send file sample when further analysis is required. We are now recommending the addition of the following settings to enable block at first sight:

Computer Configuration\Administrative Templates\Windows Components\Microsoft Defender Antivirus\MAPS\Configure the ‘Block at first sight’ feature set to Enabled

Computer Configuration\Administrative Templates\Windows Components\Microsoft Defender Antivirus\Real-time Protection\Scan all downloaded files and attachments set to Enabled

Computer Configuration\Administrative Templates\Windows Components\Microsoft Defender Antivirus\Real-time Protection\Turn off real-time protection set to Disabled

Computer Configuration\Administrative Templates\Windows Components\Microsoft Defender Antivirus\MPEngine\Select cloud protection level set to High blocking level

These new settings have been added to the MSFT Windows 10 20H2 and Server 20H2 – Defender Antivirus group policy.

For more information on block at first sight, see Turn on block at first sight.

Attack surface reduction rules

We routinely evaluate our attack surface reduction configuration and, based on diagnostic data and customer feedback, we now recommend configuring two additional attack surface reduction controls:

  • Computer Configuration\Administrative Templates\Windows Components\Microsoft Defender Antivirus\Microsoft Defender Exploit Guard\Attack Surface Reduction\Configure Attack Surface Reduction rules: Use advanced protection against ransomware
  • Block persistence through WMI event subscription.

Introduced in Windows 10, version 1709 the Use advanced protection against ransomware rule will scan any executable files and determine, using advanced cloud analytics, if the file looks malicious. If so, that file will be blocked unless it is added to an exclusion list. This rule does have a cloud dependency, so you must have Join Microsoft MAPS also configured (which is already part of the security baseline).

Block persistence through WMI event subscription is a rule that was released in Windows 10, version 1903. This rule attempts to ensure Windows Management Instrumentation (WMI) persistence—a common technique adversaries use to evade detection—is not achieved. Unlike many of the other attack surface reduction rules, this rule does not allow any sort of exclusions since it is solely based on the WMI repository.

A friendly reminder that the security baselines for Windows 10 and Windows Server, version 20H2 set all attack surface reduction rules to block mode. We recommend first configuring them to audit mode, testing to ensure you understand the impacts these rules will have in your environment, and then configuring them to block mode. Microsoft Defender for Endpoint (formally Microsoft Defender Advanced Threat Protection, or Microsoft Defender ATP) will greatly enhance the experience of testing, deploying, and managing attack surface reduction rules. We encourage you to look at evaluating, monitoring and customizing attack surface reduction rules to better prepare your environment.

These new settings have been added to the MSFT Windows 10 20H2 and Server 20H2 – Defender Antivirus group policy.

UEFI memory attribute tables

You might recall that, in the draft release of our security baseline for Windows 10, version 1809, we enabled UEFI memory attribute tables; however, based on your feedback we removed that recommendation from the final version. (Thank you to the testers who provided that feedback!) After further testing and discussions, we are again recommending that you enable the setting for Computer Configuration\Administrative Templates\System\Device Guard\Turn on Virtualization Based Security\Require UEFI Memory Attributes Table.

Microsoft Edge

Starting with Windows 10, version 20H2, Microsoft Edge on Chromium is now installed as part of the operating system. As a result, please ensure you are applying the security baseline for Microsoft Edge to your Windows 10, version 20H2 devices. We have received questions and feedback about including the Microsoft Edge in the Windows security baseline, but since Microsoft Edge is a cross-platform product and has a different release cadence, we are going to keep it a separate security baseline.

Baseline criteria

We follow a streamlined and efficient approach to defining a baseline when compared with the baselines we published before Windows 10 . The foundation of that approach is as follows:

  • Baselines are designed for well-managed, security-conscious organizations in which standard end users do not have administrative rights.
  • A baseline enforces a setting only if it mitigates a contemporary security threat and does not cause operational issues that are worse than the risks it mitigates.
  • A baseline enforces a default only if it is otherwise likely to be set to an insecure state by an authorized user:
    • If a non-administrator can set an insecure state, enforce the default.
    • If setting an insecure state requires administrative rights, enforce the default only if it is likely that a misinformed administrator will otherwise choose poorly.

For additional discussion, please see the “Why aren’t we enforcing more defaults?” section of this blog post.

 

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