Configure Trusted Roots and Disallowed Certificates

Applies To: Windows 8.1, Windows Server 2012 R2

The Windows Server 2012 R2, Windows Server 2012, Windows 8.1, and Windows 8 operating systems include an automatic update mechanism that downloads certificate trust lists (CTLs) on a daily basis. In Windows Server 2012 R2 and Windows 8.1, additional capabilities are available to control how the CTLs are updated.

Certificates and trust

The Microsoft Root Certificate Program enables distribution of trusted root certificates within Windows operating systems. For more information about the list of members in Windows Root Certificate Program, see Windows Root Certificate Program - Members List (All CAs).

Trusted root certificates are meant to be placed in the Trusted Root Certification Authorities certificate of the Windows operating systems. These certificates are trusted by the operating system and can be used by applications as a reference for which public key infrastructure (PKI) hierarchies and digital certificates that are trustworthy.

When you want to distribute trusted root certificates, the list of trusted root certificates is stored in a CTL. Client computers access the Windows Update site by using the automatic update mechanism to update this CTL.

Untrusted certificates are certificates that are publicly known to be fraudulent. Like the trusted CTL, the list of untrusted certificates is stored in a CTL. Client computers access the Windows Update site by using the automatic update mechanism to update this CTL.

Prior to Windows Server 2012 R2 and Windows 8.1 (or the installation of the software update, as previously discussed), the same registry setting controlled updates for trusted root certificates and untrusted certificates. An administrator could not selectively enable or disable one or the other. This resulting in the following challenges:

• Although disabling automatic updates for trusted CTLs is recommended for administrators who manage their lists of trusted root certificates (in disconnected or connected environments), disabling automatic updates of untrusted CTLs is not recommended.

  For more information, see Controlling the Update Root certificate Certificates Feature to Prevent the Flow of Information to and from the Internet.

• Because there was not a method for network administrators to view and extract only the trusted root certificates in a trusted CTL, managing a customized list of trusted certificates was difficult task.

Software update description

The following improved automatic update mechanisms for a disconnected environment are available in Windows Server 2012 R2 and Windows 8.1 or when the appropriate software update is installed:

• Registry settings for storing CTLs New settings enable changing the location for uploading trusted or untrusted CTLs from the Windows Update site to a shared location in an organization. For more information, see the Registry settings modified section.

• Synchronization options If the URL for the Windows Update site is moved to a local shared folder, the local shared folder must be synchronized with the Windows Update folder. This software update adds a set of options in the Certutil tool that administrators can use to enable synchronization. For more information, see the New Certutil Options section.

• Tool to select trusted root certificates This software update introduces a tool for administrators who manage the set of trusted root certificates in their enterprise environment. Administrators can view and select the set of trusted root certificates, export them to a serialized certificate store, and distribute them by using Group Policy. For more information, see the New Certutil Options section in this document.

• Independent configurability The automatic update mechanism for trusted and untrusted certificates are independently configurable. This enables administrators to use the automatic update mechanism to download only the untrusted CTLs and manage their own list of trusted CTLs. For more information, see the Registry settings modified section in this document.

Configuration options

In Windows Server 2012 R2 and Windows 8.1 (or by installing the previously mentioned software updates on supported operating systems), an administrator can configure a file or web server to download the following files by using the automatic update mechanism:

• authrootstl.cab, which contains a non-Microsoft CTL

• disallowedcertstl.cab, which contains a CTL with untrusted certificates

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

• thumbprint.crt, which 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.

By using Windows Server 2012 R2 and Windows 8.1 (or by installing the previously mentioned software updates on supported operating systems), an administrator can:

• 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 for a disconnected environment section of this document.

• Configure AD DS domain member computers to independently opt-in for untrusted and trusted CTL automatic updates. This 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. This enables administrators to select a subset of certificates to distribute by using a Group Policy Object (GPO). This is configuration is described in the Use a subset of the trusted CTLs section of this document.

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.

To configure a server that has access to the Internet to retrieve the CTL files

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 are using a scheduled task with a service account. For more information on adjusting permissions see Managing Permissions for Shared Folders.

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

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

   Substitute the actual server name for <server> and shared folder name for <share>. For example, if you run this command for a server named Server1 with a shared folder named CTL, you would 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, https://Server1/CTL).

Redirect the Microsoft Automatic Update URL for a disconnected environment

If the computers in your network are configured in a domain environment and they are unable to use the automatic update mechanism or download CTLs, you can implement a GPO in AD DS to configure those computers to obtain the CTL updates from an alternate location.

To configure a custom administrative template for a GPO

1. On a domain controller, create a new administrative template. You can start this as a text file 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.

   Tip

3. Open the Group Policy Management Editor.

   • If you are using Windows Server 2008 R2 or Windows Server 2008, click Start, and then click Run.

   • If you are using Windows Server 2012 R2 or Windows Server 2012, press the Windows key plus the R key simultaneously.

   Type GPMC.msc, and 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 cannot 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. In the Group Policy Management console, 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. Click an existing GPO or right-click and then click Create a GPO in this domain, and Link it here to create a new GPO. Right-click the GPO you want to modify and then click Edit.

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

6. Right-click Administrative Templates, and then click Add/Remove Templates.

7. In Add/Remove Templates, click Add. In the Policy Templates dialog box, select the .adm template that you previously saved. Click Open, and then click Close.

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

9. Click Windows AutoUpdate Settings, and in the details pane, double-click URL address to be used instead of default ctldl.windowsupdate.com.

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

Redirect the Microsoft Automatic Update URL for untrusted CTLs only

Some organizations may want only the untrusted CTLs (not the trusted CTLs) to be automatically updated. To accomplish this, you can create two .adm templates to add to Group Policy.

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.

   Tip

5. Open the Group Policy Management Editor.

6. In the Group Policy Management console, expand the Forest, Domains, and specific domain object that you want to modify. Right-click the Default Domain Policy GPO, and then click Edit.

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

8. Right-click Administrative Templates, and then click Add/Remove Templates.

9. In Add/Remove Templates, click Add. Use the Policy Templates dialog box to select the .adm templates that you previously saved. (You can hold the CTRL key, and click each file to select both.) Click Open, and then click Close.

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

11. Click Windows AutoUpdate Settings and then in the details pane, double-click Auto Root Update.

12. Select Disabled. This setting prevents the automatic update of the trusted CTLs. Click OK.

13. In the details pane, double-click Untrusted CTL Automatic Update. Select Enabled. Click 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.

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 complete 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

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. You can run the following command in Windows Explorer to open the WURoots.sst:

   start explorer.exe wuroots.sst
   

   Tip

   
   You can also 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. In the navigation pane of Certificate Manager, expand the file path under Certificates -Current User until you see Certificates, and then click Certificates.

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

   Important

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

5. In the Certificate Export Wizard, click Next.

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

7. On the File to Export page, enter a file path and an appropriate name for the file, such as C:\AllowedCerts.sst, and then click Next. Click Finish. When you are notified that the export was successful, click OK.

8. 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. In the Group Policy Management console, expand the Forest, Domains, and specific domain object that you want to modify. Right-click Default Domain Policy GPO, and then click Edit.

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

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

5. In the Certificate Import Wizard, click 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. Click Next.

7. Confirm that you want to place these certificates in the Trusted Root Certification Authorities certificate store by clicking Next. Click Finish. When you are notified that the certificates imported successfully, click 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 are not automatically removed if the GPO is unlinked or removed from the domain. These settings must be specifically reconfigured, if you want to change them.

New Certutil Options

The following options were added to Certutil:

Potential errors with Certutil -SyncWithWU

You may encounter the following errors and warnings when running the Certutil -syncWithWU command:

• If you use a non-existent local path or folder as the destination folder, you will see the error:

  The system cannot find the file specified. 0x80070002 (WIN32: 2 ERROR_FILE_NOT_FOUND)

• If you use a non-existent or unavailable network location as the destination folder, you will see the error:

  The network name cannot be found. 0x80070043 (WIN32: 67 ERROR_BAD_NET_NAME)

• If your server cannot connect over TCP port 80 to Microsoft Automatic Update servers, you will receive the following error:

  A connection with the server could not be established 0x80072efd (INet: 12029 ERROR_INTERNET_CANNOT_CONNECT)

• If your server is unable to reach the Microsoft Automatic Update servers with the DNS name ctldl.windowsupdate.com, you will receive the following error:

  The server name or address could not be resolved 0x80072ee7 (INet: 12007 ERROR_INTERNET_NAME_NOT_RESOLVED).

• If you do not use the -f switch, and any of the CTL files already exist in the directory, you will receive a file exists error:

  CertUtil: -syncWithWU command FAILED: 0x800700b7 (WIN32/HTTP: 183 ERROR_ALREADY_EXISTS) Certutil: Cannot create a file when that file already exists.

• If there is a change in the trusted root certificates, you will see: "Warning! Encountered the following no longer trusted roots: <folder path>\<thumbprint>.crt. Use "-f -f" options to force the delete of the above ".crt" files. Was "authrootstl.cab" updated? If yes, consider deferring the delete until all clients have been updated."

Related content

• How to Write a Simple .Adm File for Registry-based Group Policy

• Managing Group Policy ADMX Files Step-by-Step Guide

• Windows Root certificate Certificate Program - Members List (All CAs)

• Controlling the Update Root certificate Certificates Feature to Prevent the Flow of Information to and from the Internet

• Windows Server Security Forum

• Active Directory Certificate Services (AD CS) Public Key Infrastructure (PKI) Frequently Asked Questions (FAQ)

• Windows PKI Documentation Reference and Library

• Windows PKI Blog