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Configure trusted roots and disallowed certificates in Windows

Redirect the Microsoft Automatic Update URL to a file or web server hosting Certificate Trust Lists (CTLs), untrusted CTLs, or a subset of the trusted CTL files in a disconnected environment.

To learn more about how the Microsoft Root Certificate Program works to distribute trusted root certificates automatically across Windows operating systems, see Certificates and trust.

Tip

You don't need to redirect the Microsoft Automatic Update URL for environments where computers are able to connect to the Windows Update site directly. Computers that can connect to the Windows Update site are able to receive updated CTLs on a daily basis.

Prerequisites

Before you can configure your disconnected environment to use CTL files hosted on a file or web server, you need to complete the following prerequisites.

Client prerequisites

  • At least one computer that is able to connect to the Internet to download CTLs from Microsoft. The computer requires HTTP (TCP port 80) access and name resolution (TCP and UDP port 53) ability to contact ctldl.windowsupdate.com. This computer can be a domain member or a member of a workgroup. Currently all the downloaded files require approximately 1.5 MB of space.
  • Client machines must be connected to an Active Directory Domain Service domain.
  • You must be a member of the local Administrators group.

Server prerequisites

  • A file server or web server for hosting the CTL files.
  • AD Group policy or MDM solution to deploy configuration settings to your client.
  • An account that is a member of the Domain Admins group or that has been delegated the necessary permissions

Configuration methods

An administrator can configure a file or web server to download the following files by using the automatic update mechanism:

  • authrootstl.cab contains a non-Microsoft CTL.

  • disallowedcertstl.cab contains a CTL with untrusted certificates.

  • disallowedcert.sst contains a serialized certificate store, including untrusted certificates.

  • <thumbprint>.crt contains non-Microsoft root certificates.

The steps to perform this configuration are described in the Configure a file or web server to download the CTL files section of this document.

There are several methods to configure your environment to use local CTL files or a subset of trusted CTLs. The following methods are available.

  • Configure Active Directory Domain Services (AD DS) domain member computers to use the automatic update mechanism for trusted and untrusted CTLs, without having access to the Windows Update site. This configuration is described in the Redirect the Microsoft Automatic Update URL section of this document.

  • Configure AD DS domain member computers to independently opt-in for untrusted and trusted CTL automatic updates. The independent opt-in configuration is described in the Redirect the Microsoft Automatic Update URL for untrusted CTLs only section of this document.

  • Examine the set of root certificates in the Windows Root Certificate Program. Examining the root certificate set enables administrators to select a subset of certificates to distribute by using a Group Policy Object (GPO). This configuration is described in the Use a subset of the trusted CTLs section of this document.

Important

  • The settings described in this document are implemented by using GPOs. These settings are not automatically removed if the GPO is unlinked or removed from the AD DS domain. When implemented, these settings can be changed only by using a GPO or by modifying the registry of the affected computers.

  • The concepts discussed in this document are independent of Windows Server Update Services (WSUS).

Configure a file or web server to download the CTL files

To facilitate the distribution of trusted or untrusted certificates for a disconnected environment, you must first configure a file or web server to download the CTL files from the automatic update mechanism.

Retrieve the CTL files from Windows Update

  1. Create a shared folder on a file or web server that is able to synchronize by using the automatic update mechanism and that you want to use to store the CTL files.

    Tip

    Before you begin, you may have to adjust the shared folder permissions and NTFS folder permissions to allow the appropriate account access, especially if you're using a scheduled task with a service account. For more information on adjusting permissions, see Managing Permissions for Shared Folders.

  2. From an elevated PowerShell prompt, run the following command:

    Certutil -syncWithWU \\<server>\<share>

    Substitute the actual server name for <server> and shared folder name for <share> For example, for a server named Server1 with a shared folder named CTL, you'd run the command:

    Certutil -syncWithWU \\Server1\CTL

  3. Download the CTL files on a server that computers on a disconnected environment can access over the network by using a FILE path (for example, FILE://\\Server1\CTL) or an HTTP path (for example, http://Server1/CTL).

Note

  • If the server that synchronizes the CTLs is not accessible from the computers in the disconnected environment, you must provide another method to transfer the information. For example, you can allow one of the domain members to connect to the server, then schedule another task on the domain member computer to pull the information into a shared folder on an internal web server. If there is absolutely no network connection, you may have to use a manual process to transfer the files, such as a removable storage device.

  • If you plan to use a web server, you should create a new virtual directory for the CTL files. The steps to create a virtual directory by using Internet Information Services (IIS) are nearly the same for all the supported operating systems discussed in this document. For more information, see Create a Virtual Directory (IIS7).

  • Certain system and application folders in Windows have special protection applied to them. For example, the inetpub folder requires special access permissions, which make it difficult to create a shared folder for use with a scheduled task to transfer files. An administrator can create a folder location at the root of a logical drive system to use for file transfers.

Redirect the Microsoft Automatic Update URL

The computers in your network might be configured in a disconnected environment and therefore unable to use the automatic update mechanism or download CTLs. You can implement a GPO in AD DS to configure these computers to obtain the CTL updates from an alternate location.

The configuration in this section requires that you already completed the steps in Configure a file or web server to download the CTL files.

To configure a custom administrative template for a GPO

  1. On a domain controller, create a new administrative template. Open a text file in Notepad and then change the file name extension to .adm. The contents of the file should be as follows:

    CLASS MACHINE
CATEGORY !!SystemCertificates
    KEYNAME "Software\Microsoft\SystemCertificates\AuthRoot\AutoUpdate"
    POLICY !!RootDirURL
       EXPLAIN !!RootDirURL_help
       PART !!RootDirURL EDITTEXT
             VALUENAME "RootDirURL"
       END PART
    END POLICY
END CATEGORY
[strings]
RootDirURL="URL address to be used instead of default ctldl.windowsupdate.com"
RootDirURL_help="Enter a FILE or HTTP URL to use as the download location of the CTL files."
SystemCertificates="Windows AutoUpdate Settings"

  2. Use a descriptive name to save the file, such as RootDirURL.adm.

    • Ensure that the file name extension is .adm and not .txt.

    • If you haven't already enabled file name extension viewing, see How To: View File Name Extensions.

    • If you save the file to the %windir%\inf folder, it's easier to locate in the following steps.

  3. Open the Group Policy Management Editor. Select Start > Run, type GPMC.msc, then press ENTER.

    Warning

    You can link a new GPO to the domain or to any organizational unit (OU). The GPO modifications implemented in this document alter the registry settings of the affected computers. You can't undo these settings by deleting or unlinking the GPO. The settings can only be undone by reversing them in the GPO settings or by modifying the registry using another technique.

  4. Expand the Forest object, expand the Domains object, and then expand the specific domain that contains the computer accounts that you want to change. If you have a specific OU that you want to modify, then navigate to that location.

  5. Right-select and then select Create a GPO in this domain, and Link it here to create a new GPO.

  6. In the navigation pane, under Computer Configuration, expand Policies.

  7. Right-select Administrative Templates, then select Add/Remove Templates.

  8. In Add/Remove Templates, select Add.

  9. In the Policy Templates dialog box, select the .adm template that you previously saved. Select Open, then select Close.

  10. In the navigation pane, expand Administrative Templates, and then expand Classic Administrative Templates (ADM).

  11. Select Windows AutoUpdate Settings, and in the details pane, double-select URL address to be used instead of default ctldl.windowsupdate.com.

  12. Select Enabled. In the Options section, enter the URL to the file server or web server that contains the CTL files. For example, http://server1/CTL or file://\\server1\CTL.

  13. Select OK.

  14. Close the Group Policy Management Editor.

The policy is effective immediately, but the client computers must be restarted to receive the new settings, or you can type gpupdate /force from an elevated command prompt or from Windows PowerShell.

Important

The trusted and untrusted CTLs can be updated on a daily basis, so ensure that you keep the files synchronized by using a scheduled task or another method (such as a script that handles error conditions) to update the shared folder or web virtual directory. For more information about creating a scheduled task using PowerShell, see New-ScheduledTask. If you plan to write a script to make daily updates, see the certutil Windows command reference.

Redirect the Microsoft Automatic Update URL for untrusted CTLs only

Some organizations might want only the untrusted CTLs (not the trusted CTLs) to be automatically updated. To automatically update only the untrusted CTLs, create two .adm templates to add to Group Policy.

In a disconnected environment, you can use the following procedure with the previous procedure (redirect the Microsoft Automatic Update URL for trusted CTLs and untrusted CTLs). This procedure explains how to selectively disable the automatic update of trusted CTLs.

You also can use this procedure in a connected environment in isolation to selectively disable the automatic update of trusted CTLs.

To selectively redirect only untrusted CTLs

  1. On a domain controller, create the first new administrative template by starting with a text file and then changing the file name extension to .adm. The contents of the file should be as follows:

    CLASS MACHINE
CATEGORY !!SystemCertificates
    KEYNAME "Software\Policies\Microsoft\SystemCertificates\AuthRoot"
    POLICY !!DisableRootAutoUpdate
       EXPLAIN !!Certificates_config
       VALUENAME "DisableRootAutoUpdate"
       VALUEON NUMERIC 0
          VALUEOFF NUMERIC 1

    END POLICY
END CATEGORY
[strings]
DisableRootAutoUpdate="Auto Root Update"
Certificates_config="By default automatic updating of the trusted CTL is enabled. To disable the automatic updating trusted CTLe, select Disabled."
SystemCertificates="Windows AutoUpdate Settings"

  2. Use a descriptive name to save the file, such as DisableAllowedCTLUpdate.adm.

  3. Create a second new administrative template. The contents of the file should be as follows:

    CLASS MACHINE
CATEGORY !!SystemCertificates
    KEYNAME "Software\Policies\Microsoft\SystemCertificates\AuthRoot"
    POLICY !!EnableDisallowedCertAutoUpdate
       EXPLAIN !!Certificates_config
       VALUENAME "EnableDisallowedCertAutoUpdate"
       VALUEON NUMERIC 1
          VALUEOFF NUMERIC 0

    END POLICY
END CATEGORY
[strings]
EnableDisallowedCertAutoUpdate="Untrusted CTL Automatic Update"
Certificates_config="By default untrusted CTL automatic update is enabled. To disable trusted CTL update, select Disabled."
SystemCertificates="Windows AutoUpdate Settings"

  4. Use a descriptive file name to save the file, such as EnableUntrustedCTLUpdate.adm.

    • Ensure that the file name extensions of these files are .adm and not .txt.

    • If you save the file to the %windir%\inf folder, it's easier to locate in the following steps.

  5. Open the Group Policy Management Editor.

  6. Expand the Forest object, expand the Domains object, and then expand the specific domain that contains the computer accounts that you want to change. If you have a specific OU that you want to modify, then navigate to that location.

  7. In the navigation pane, under Computer Configuration, expand Policies.

  8. Right-select Administrative Templates, then select Add/Remove Templates.

  9. In Add/Remove Templates, select Add.

  10. In the Policy Templates dialog box, select the .adm template that you previously saved. Select Open, then select Close.

  11. In the navigation pane, expand Administrative Templates, then expand Classic Administrative Templates (ADM).

  12. Select Windows AutoUpdate Settings, then in the details pane, double-click Auto Root Update.

  13. Select Disabled, then select OK.

  14. In the details pane, double-click Untrusted CTL Automatic Update, then select Enabled and OK.

The policy is effective immediately, but the client computers must be restarted to receive the new settings, or you can type gpupdate /force from an elevated command prompt or from Windows PowerShell.

Important

The trusted and untrusted CTLs can be updated on a daily basis, so ensure that you keep the files synchronized by using a scheduled task or another method to update the shared folder or virtual directory.

Use a subset of the trusted CTLs

This section describes how you can produce, review, and filter the trusted CTLs that you want computers in your organization to use. You must implement the GPOs described in the previous procedures to make use of this resolution. This resolution is available for disconnected and connected environments.

There are two procedures to customize the list of trusted CTLs.

  1. Create a subset of trusted certificates

  2. Distribute the trusted certificates by using Group Policy

To create a subset of trusted certificates

Here's how to generate SST files by using the automatic Windows update mechanism from Windows. For more information about generating SST files, see the Certutil Windows commands reference.

  1. From a computer that is connected to the Internet, open Windows PowerShell as an Administrator or open an elevated command prompt, and type the following command:

    Certutil -generateSSTFromWU WURoots.sst

  2. Run the following command in Windows Explorer to open WURoots.sst:

    start explorer.exe wuroots.sst

    Tip

    You also can use Internet Explorer to navigate to the file and double-click it to open it. Depending on where you stored the file, you may also be able to open it by typing wuroots.sst.

  3. Open Certificate Manager.

  4. Expand the file path under Certificates - Current User until you see Certificates, then select Certificates.

  5. In the details pane, you can see the trusted certificates. Hold down the CTRL key and select each of the certificates that you want to allow. When you've finished selecting the certificates you want to allow, right-click one of the selected certificates, select All Tasks, then select Export.

    • You must select a minimum of two certificates to export the .sst file type. If you select only one certificate, the .sst file type isn't available, and the .cer file type is selected instead.

  6. In the Certificate Export Wizard, select Next.

  7. On the Export File Format page, select Microsoft Serialized Certificate Store (.SST), and then select Next.

  8. On the File to Export page, enter a file path and an appropriate name for the file, such as C:\AllowedCerts.sst, then select Next.

  9. Select Finish. When you're notified that the export was successful, select OK.

  10. Copy the .sst file that you created to a domain controller.

To distribute the list of trusted certificates by using Group Policy

  1. On the domain controller that has the customized .sst file, open the Group Policy Management Editor.

  2. Expand the Forest, Domains, and specific domain object that you want to modify. Right-click Default Domain Policy GPO, then select Edit.

  3. In the navigation pane, under Computer Configuration, expand Policies, expand Windows Settings, expand Security Settings, then expand Public Key Policies.

  4. Right-click Trusted Root Certification Authorities, then select Import.

  5. In the Certificate Import Wizard, select Next.

  6. Enter the path and file name of the file that you copied to the domain controller, or use the Browse button to locate the file. Select Next.

  7. Confirm that you want to place these certificates in the Trusted Root Certification Authorities certificate store by selecting Next. select Finish. When you're notified that the certificates imported successfully, select OK.

  8. Close the Group Policy Management Editor.

The policy is effective immediately, but the client computers must be restarted to receive the new settings, or you can type gpupdate /force from an elevated command prompt or from Windows PowerShell.

Registry settings modified

The settings described in this document configure the following registry keys on the client computers. These settings aren't automatically removed if the GPO is unlinked or removed from the domain. These settings must be reconfigured, if you want to change them.

  • Enable or disable the Windows AutoUpdate of the trusted CTL:

    • Key: HKLM\SOFTWARE\Policies\Microsoft\SystemCertificates\AuthRoot\DisableRootAutoUpdate
    • Type: REG_DWORD
    • Name: DisableRootAutoUpdate
    • Data: 0 to enabled or 1 to disable.
    • Default: There is no key present by default. Without a key present, the default is enabled.

  • Enable or disable the Windows AutoUpdate of the untrusted CTL:

    • Key: SOFTWARE\Policies\Microsoft\SystemCertificates\AuthRoot
    • Type: REG_DWORD
    • Name: EnableDisallowedCertAutoUpdate
    • Data: 1 to enabled or 0 to disable.
    • Default: There is no key present by default. Without a key present, the default is enabled.

  • Set the shared CTL file location (HTTP or the FILE path):

    • Key: HKLM\SOFTWARE\Microsoft\SystemCertificates\AuthRoot\AutoUpdate\RootDirUrl
    • Type: REG_SZ
    • Name: RootDirUrl
    • Data: Enter a valid HTTP or file URI.
    • Default: There is no key present by default. Without a key present, the default behavior used Windows Update.

Verify Trusted and Untrusted CTLs

It may be necessary for various reasons to verify all Trusted and Untrusted CTLs from a client machine. The following Certutil options can be used to verify all Trusted and Untrusted CTLs from a client machine.

certutil -verifyCTL AuthRoot
certutil -verifyCTL Disallowed

Checking Last Sync Time

To check the most recent sync time on the local machine for either Trusted or Untrusted CTLs, run the following Certutil command:

certutil -verifyctl AuthRoot | findstr /i "lastsynctime"
certutil -verifyctl Disallowed | findstr /i "lastsynctime"