Windows Server guidance to protect against speculative execution side-channel vulnerabilities

Hutumika kwa: Windows Server 2016 Version 1709Windows Server 2012 R2 StandardWindows Server 2012 Standard Zaidi

Summary


Microsoft is aware of a new publicly disclosed class of vulnerabilities that are called “speculative execution side-channel attacks” and that affect many modern processors including Intel, AMD, and ARM.

Note This issue also affects other operating systems, such as Android, Chrome, iOS, and macOS. Therefore, we advise customers to seek guidance from those vendors.

Microsoft has released several updates to help mitigate these vulnerabilities. We have also taken action to secure our cloud services. See the following sections for more details.

Microsoft has not yet received any information to indicate that these vulnerabilities have been used to attack customers. Microsoft is working closely with industry partners including chip makers, hardware OEMs, and app vendors to protect customers. To get all available protections, firmware (microcode) and software updates are required. This includes microcode from device OEMs and, in some cases, updates to antivirus software.

This article addresses the following vulnerabilities:

To learn more about this class of vulnerabilities, see ADV180002 and ADV180012.

Microsoft provides third-party contact information to help you find technical support. This contact information may change without notice. Microsoft does not guarantee the accuracy of this third-party contact information.

Recommended actions


Customers should take the following actions to help protect against the vulnerabilities:

  1. Apply all available Windows operating system updates, including the monthly Windows security updates. For details about how to enable these updates, see Microsoft Knowledge Base article 4072699.
  2. Apply applicable firmware (microcode) updates from the device manufacturer (OEM).
  3. Evaluate the risk to your environment based on the information that's in Microsoft Security Advisories ADV180002 and ADV180012 and in this Knowledge Base article.
  4. Take action as required by using the advisories and registry key information that is provided in this Knowledge Base article.

Mitigation Settings for Windows Server


Security advisories ADV180002 and ADV180012 provide information on the risk posed by these vulnerabilities and identify the default state of mitigations for Windows Server systems. The below table summarizes the requirement of CPU microcode and the default status of the mitigations on Windows Server.

CVE Requires CPU microcode/firmware? Mitigation Default status

CVE-2017-5753

No

Enabled by default (no option to disable)

CVE-2017-5715

Yes

Disabled by default.

CVE-2017-5754

No

Windows Server 2019: Enabled by default.
Windows Server 2016 and earlier: Disabled by default.

CVE-2018-3639

Intel: Yes

AMD: No

Disabled by default. See ADV180012 for more information and this KB article for applicable registry key settings.

Customers who want to obtain all available protections against these vulnerabilities must make registry key changes to enable these mitigations that are disabled by default.

Enabling these mitigations may affect performance. The scale of the performance effects depends on multiple factors, such as the specific chipset in your physical host and the workloads that are running. We recommend that customers assess the performance effects for their environment and make any necessary adjustments.

Your server is at increased risk if it's in one of the following categories:

  • Hyper-V hosts – Requires protection for VM-to-VM and VM-to-host attacks.
  • Remote Desktop Services Hosts (RDSH) – Requires protection from one session to another session or from session-to-host attacks.
  • Physical hosts or virtual machines that are running untrusted code, such as containers or untrusted extensions for database, untrusted web content, or workloads that run code that's from external sources. These require protection from untrusted process-to-another-process or untrusted-process-to-kernel attacks.

Use the following registry key settings to enable the mitigations on the server, and restart the system for the changes to take effect.

Important This section, method, or task contains steps that tell you how to modify the registry. However, serious problems might occur if you modify the registry incorrectly. Therefore, make sure that you follow these steps carefully. For added protection, back up the registry before you modify it. Then, you can restore the registry if a problem occurs. For more information about how to back up and restore the registry, click the following article number to view the article in the Microsoft Knowledge Base:

 

322756 How to back up and restore the registry in Windows

Manage mitigations for CVE-2017-5715 (Spectre Variant 2) and CVE-2017-5754 (Meltdown)


To enable mitigations for CVE-2017-5715 (Spectre Variant 2) and CVE-2017-5754 (Meltdown)

reg add "HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager\Memory Management" /v FeatureSettingsOverride /t REG_DWORD /d 0 /f

reg add "HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager\Memory Management" /v FeatureSettingsOverrideMask /t REG_DWORD /d 3 /f

reg add "HKLM\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Virtualization" /v MinVmVersionForCpuBasedMitigations /t REG_SZ /d "1.0" /f

If this is a Hyper-V host and the firmware updates have been applied: Fully shut down all Virtual Machines. This enables the firmware-related mitigation to be applied on the host before the VMs are started. Therefore, the VMs are also updated when they're restarted.

Restart the computer for the changes to take effect.

To disable mitigations for CVE-2017-5715 (Spectre Variant 2) and CVE-2017-5754 (Meltdown)

reg add "HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager\Memory Management" /v FeatureSettingsOverride /t REG_DWORD /d 3 /f

reg add "HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager\Memory Management" /v FeatureSettingsOverrideMask /t REG_DWORD /d 3 /f

Restart the computer for the changes to take effect.


Note 
Setting FeatureSettingsOverrideMask to 3 is accurate for both the "enable" and "disable" settings. (See the "FAQ" section for more details about registry keys.)

Manage the mitigation for CVE-2017-5715 (Spectre Variant 2)


To disable Variant 2: (CVE-2017-5715  "Branch Target Injection") mitigation:

reg add "HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager\Memory Management" /v FeatureSettingsOverride /t REG_DWORD /d 1 /f

reg add "HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager\Memory Management" /v FeatureSettingsOverrideMask /t REG_DWORD /d 3 /f

Restart the computer for the changes to take effect.

To enable Variant 2: (CVE-2017-5715  "Branch Target Injection") mitigation:

reg add "HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager\Memory Management" /v FeatureSettingsOverride /t REG_DWORD /d 0 /f

reg add "HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager\Memory Management" /v FeatureSettingsOverrideMask /t REG_DWORD /d 3 /f

Restart the computer for the changes to take effect.

AMD processors only: Enable the full mitigation for CVE-2017-5715 (Spectre Variant 2)


By default, user-to-kernel protection for CVE-2017-5715 is disabled for AMD CPUs. Customers must enable the mitigation to receive additional protections for CVE-2017-5715.  For more information, see FAQ #15 in ADV180002.

Enable user-to-kernel protection on AMD processors along with other protections for CVE 2017-5715:

reg add "HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager\Memory Management" /v FeatureSettingsOverride /t REG_DWORD /d 64 /f

reg add "HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager\Memory Management" /v FeatureSettingsOverrideMask /t REG_DWORD /d 3 /f

reg add "HKLM\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Virtualization" /v MinVmVersionForCpuBasedMitigations /t REG_SZ /d "1.0" /f

If this is a Hyper-V host and the firmware updates have been applied: Fully shut down all Virtual Machines. This enables the firmware-related mitigation to be applied on the host before the VMs are started. Therefore, the VMs are also updated when they're restarted.

Restart the computer for the changes to take effect.

Manage mitigations for CVE-2018-3639 (Speculative Store Bypass), CVE-2017-5715 (Spectre Variant 2), and CVE-2017-5754 (Meltdown)



To enable mitigations for CVE-2018-3639 (Speculative Store Bypass), CVE-2017-5715 (Spectre Variant 2), and CVE-2017-5754 (Meltdown):

reg add "HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager\Memory Management" /v FeatureSettingsOverride /t REG_DWORD /d 8 /f

reg add "HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager\Memory Management" /v FeatureSettingsOverrideMask /t REG_DWORD /d 3 /f

reg add "HKLM\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Virtualization" /v MinVmVersionForCpuBasedMitigations /t REG_SZ /d "1.0" /f

If this is a Hyper-V host and the firmware updates have been applied: Fully shut down all Virtual Machines. This enables the firmware-related mitigation to be applied on the host before the VMs are started. Therefore, the VMs are also updated when they're restarted.

Restart the computer for the changes to take effect.

To disable mitigations for CVE-2018-3639 (Speculative Store Bypass) AND mitigations for CVE-2017-5715 (Spectre Variant 2)  and CVE-2017-5754 (Meltdown)

reg add "HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager\Memory Management" /v FeatureSettingsOverride /t REG_DWORD /d 3 /f

reg add "HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager\Memory Management" /v FeatureSettingsOverrideMask /t REG_DWORD /d 3 /f

Restart the computer for the changes to take effect.

 

AMD processors only: Enable the full mitigation for CVE-2017-5715 (Spectre Variant 2) and CVE 2018-3639 (Speculative Store Bypass)


By default, user-to-kernel protection for CVE-2017-5715 is disabled for AMD processors. Customers must enable the mitigation to receive additional protections for CVE-2017-5715.  For more information, see FAQ #15 in ADV180002.

Enable user-to-kernel protection on AMD processors along with other protections for CVE 2017-5715 and protections for CVE-2018-3639 (Speculative Store Bypass):

reg add "HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager\Memory Management" /v FeatureSettingsOverride /t REG_DWORD /d 72 /f

reg add "HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager\Memory Management" /v FeatureSettingsOverrideMask /t REG_DWORD /d 3 /f

reg add "HKLM\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Virtualization" /v MinVmVersionForCpuBasedMitigations /t REG_SZ /d "1.0" /f

If this is a Hyper-V host and the firmware updates have been applied: Fully shut down all Virtual Machines. This enables the firmware-related mitigation to be applied on the host before the VMs are started. Therefore, the VMs are also updated when they're restarted.

Restart the computer for the changes to take effect.

Verifying that protections are enabled


To help customers verify that protections are enabled, Microsoft has published a PowerShell script that customers can run on their systems. Install and run the script by running the following commands.

PowerShell verification by using the PowerShell Gallery (Windows Server 2016 or WMF 5.0/5.1)

Install the PowerShell Module:

PS> Install-Module SpeculationControl

Run the PowerShell module to verify that protections are enabled:

PS> # Save the current execution policy so it can be reset

PS> $SaveExecutionPolicy = Get-ExecutionPolicy

PS> Set-ExecutionPolicy RemoteSigned -Scope Currentuser

PS> Import-Module SpeculationControl

PS> Get-SpeculationControlSettings

PS> # Reset the execution policy to the original state

PS> Set-ExecutionPolicy $SaveExecutionPolicy -Scope Currentuser

PowerShell verification by using a download from Technet (Earlier operating system versions and Earlier WMF versions)

Install the PowerShell module from Technet ScriptCenter:

  1. Go to https://aka.ms/SpeculationControlPS.
  2. Download SpeculationControl.zip to a local folder.
  3. Extract the contents to a local folder. For example: C:\ADV180002

Run the PowerShell module to verify that protections are enabled:

Start PowerShell, and then use the previous example to copy and run the following commands:

PS> # Save the current execution policy so it can be reset

PS> $SaveExecutionPolicy = Get-ExecutionPolicy

PS> Set-ExecutionPolicy RemoteSigned -Scope Currentuser

PS> CD C:\ADV180002\SpeculationControl

PS> Import-Module .\SpeculationControl.psd1

PS> Get-SpeculationControlSettings

PS> # Reset the execution policy to the original state

PS> Set-ExecutionPolicy $SaveExecutionPolicy -Scope Currentuser


For a detailed explanation of the output of the PowerShell script, see
Knowledge Base article 4074629

Frequently asked questions


I wasn't offered the Windows security updates that were released in January and February 2018. What should I do?

To help avoid adversely affecting customer devices, the Windows security updates that were released in January and February 2018 were not offered to all customers. For details, see Microsoft Knowledge Base article 4072699.

References