DirectAccess and OTP with PointSharp ID Webinar

Integrating multifactor authentication is essential for providing the highest level of security and assurance for DirectAccess clients. Smart cards work well for this, but they impose a heavy burden in terms of expense and administrative overhead. A more effective alternative is to use a One-Time Password (OTP) solution such as PointSharp ID.

DirectAccess and PointSharp ID Webinar

To learn more about the PointSharp ID OTP solution and how it integrates with DirectAccess, join me for a live webinar on Tuesday, July 27, 2106 at 10:00AM PDT where I’ll discuss the following topics.

  • What DirectAccess security risks can be mitigated with OTP?
  • What are the supporting infrastructure requirements for OTP authentication?
  • How to integrate the PointSharp IP solution with DirectAccess

You can register for this free live webinar here.

DirectAccess IP-HTTPS Preauthentication


Introduction

DirectAccess IP-HTTPS PreauthenticationRecently I’ve written about the security challenges with DirectAccess, specifically around the use of the IP-HTTPS IPv6 transition technology. In its default configuration, the DirectAccess server does not authenticate the client when an IP-HTTPS transition tunnel is established. This opens up the possibility of an unauthorized user launching Denial-of-Service (DoS) attacks and potentially performing network reconnaissance using ICMPv6. More details on this can be found here.

Mitigation

The best way to mitigate these security risks is to implement an Application Delivery Controller (ADC) such as the F5 BIG-IP Local Traffic Manager or the Citrix NetScaler. I’ve documented how to configure those platforms here and here.

No ADC?

For those organizations that do not have a capable ADC deployed, it is possible to configure the IP-HTTPS listener on the Windows Server 2012 R2 server itself to perform preauthentication.

Important Note: Making the following changes on the DirectAccess server is not formally supported. Also, this change is incompatible with one-time passwords (OTP)  and should not be performed if strong user authentication is enabled. In addition, null cipher suites will be disabled, resulting in reduced scalability and degraded performance for Windows 8.x and Windows 10 clients. Making this change should only be done if a suitable ADC is not available.

Configure IP-HTTPS Preauthentication

To configure the DirectAccess server to perform preauthentication for IP-HTTPS connections, open an elevated PowerShell command window and enter the following command.

ls Cert:\LocalMachine\My

DirectAccess IP-HTTPS Preauthentication

Copy the thumbprint that belongs to the SSL certificate assigned to the IP-HTTPS listener. Open an elevated command prompt window (not a PowerShell window!) and enter the following commands.

netsh http delete sslcert ipport=0.0.0.0:443
netsh http add sslcert ipport=0.0.0.0:443 certhash=[thumbprint]
appid={5d8e2743-ef20-4d38-8751-7e400f200e65}
dsmapperusage=enable clientcertnegotiation=enable

DirectAccess IP-HTTPS Preauthentication

For load-balanced clusters and multisite deployments, repeat these steps on each DirectAccess server in the cluster and/or enterprise.

Summary

Once these changes have been made, only DirectAccess clients that have a computer certificate with a subject name that matches the name of its computer account in Active Directory will be allowed to establish an IP-HTTPS transition tunnel connection.

DirectAccess IP-HTTPS Preauthentication using F5 BIG-IP

Note: For information about configuring the Citrix NetScaler to perform IP-HTTPS preauthentication, click here. For information about configuring Windows Server 2012 R2 to perform IP-HTTPS preauthentication natively, click here.

Introduction

DirectAccess IP-HTTPS Preauthentication using F5 BIG-IPRecently I wrote about security challenges with DirectAccess and the IP-HTTPS IPv6 transition technology. Specifically, IP-HTTPS transition tunnel connections are not authenticated by the DirectAccess server, only the client. This allows an unauthorized device to obtain an IPv6 address on the DirectAccess client network. With it, an attacker can perform network reconnaissance using ICMPv6 and potentially launch a variety of Denial-of-Service (DoS) attacks. For more details, click here.

Note: DirectAccess IPsec data connections not at risk. Data is never exposed at any time with the default configuration.

Mitigation

To mitigate these issues, it is recommended that an Application Delivery Controller (ADC) be used to terminate SSL connections and enforce client certificate authentication. Doing this will ensure that only authorized connections will be accepted by the DirectAccess server. In addition, there are some scalability and performance benefits to implementing this configuration when supporting Windows 7 clients.

Important Considerations

Performing IP-HTTPS preauthentication on the F5 BIG-IP is formally unsupported by Microsoft. In addition, terminating IP-HTTPS on the F5 appliance breaks OTP authentication.

F5 BIG-IP Configuration

To configure the F5 BIG-IP to perform SSL offload for DirectAccess IP-HTTPS, follow the guidance documented here. In addition, to configure the F5 BIG-IP to perform preauthentication for DirectAccess clients, when creating the client SSL profile, click Custom above the Client Authentication section and choose Require from the Client Certificate drop-down list and Always from the Frequency drop-down list. In addition, choose your internal PKI’s root Certification Authority (CA) certificate from the Trusted Certificate Authorities drop-down list and from the Advertised Certificate Authorities drop-down list.

DirectAccess IP-HTTPS Preauthentication using F5 BIG-IP

Summary

Enabling client certificate authentication for IP-HTTPS connections ensures that only authorized DirectAccess clients can establish a connection to the DirectAccess server and obtain an IPv6 address. It also prevents an unauthorized user from performing network reconnaissance or launching IPv6 Denial-of-Service (DoS) attacks.

DirectAccess IP-HTTPS Preauthentication using Citrix NetScaler

Note: For information about configuring the F5 BIG-IP to perform IP-HTTPS preauthentication, click hereFor information about configuring Windows Server 2012 R2 or Windows Server 2016 to perform IP-HTTPS preauthentication natively, click here.

Introduction

DirectAccess IP-HTTPS Preauthentication using Citrix NetScalerIP-HTTPS is an IPv6 transition technology used by DirectAccess. It enables DirectAccess clients to communicate with the DirectAccess server using IPv6 over the public IPv4 Internet by encapsulating IPv6 packets in HTTP and authenticating (and optionally encrypting) them using SSL/TLS. IP-HTTPS is supported for all DirectAccess network deployment configurations and is enabled by default.

When a DirectAccess client connection is established, only the server is authenticated by the client. The client is not authenticated by the server. The DirectAccess server will thus accept IP-HTTPS connections from any client, valid or not.

IP-HTTPS Connection

Once a client has established an IP-HTTPS transition tunnel, it will go through the standard IPv6 neighbor discovery process to identify routers and obtain an IPv6 prefix for the link. It will use this information to build its own IPv6 address, which it uses to communicate with the DirectAccess server and begin establishing IPsec security associations for DirectAccess.

ICMP and IPsec

By design, ICMP is exempt from DirectAccess IPsec policy processing. If an unauthorized client were to establish an IP-HTTPS transition tunnel, even without authentication (Kerberos Proxy or certificate) it would be able to ping the DirectAccess server tunnel endpoint IPv6 addresses, the DNS64 IPv6 address, and any intranet hosts (assuming host firewalls allow this access).

Security Risk

This default posture opens up the DirectAccess server and intranet to unauthorized remote network reconnaissance and some IPv6-related Denial-of-Service (DoS) attacks. These were demonstrated by security researcher Ali Hardudi at the recent Troopers16 security conference. You can view his very informative session here.

Note: DirectAccess IPsec data connections are unaffected and are completely secure. Data is never exposed at any time with the default configuration.

IP-HTTPS Preauthentication

DirectAccess IP-HTTPS Preauthentication using Citrix NetScalerTo mitigate these risks, it is recommended that an Application Delivery Controller (ADC) such as the Citrix NetScaler be configured to preauthenticate DirectAccess clients prior to establishing the IP-HTTPS transition tunnel.

Note: To configure the F5 BIG-IP to perform IP-HTTPS preauthentication, click here.

Citrix NetScaler Configuration

To perform DirectAccess preauthentication, it will be necessary to configure the Citrix NetScaler to perform SSL termination for IP-HTTPS. The virtual server on the NetScaler must use the SSL protocol. In addition, a CA certificate must be bound to the virtual server. Also, Client Authentication must be enabled under SSL Parameters and be set to Mandatory.

DirectAccess IP-HTTPS Preauthentication using Citrix NetScaler

Once configured, the NetScaler appliance will ensure that the DirectAccess IPsec certificate is present on the client before establishing the IP-HTTPS IPv6 transition tunnel. This will prevent unauthorized connections to the DirectAccess server.

Important Considerations

Performing IP-HTTPS preauthentication on the Citrix NetScaler is formally unsupported by Microsoft. In addition, terminating IP-HTTPS on the NetScaler appliance breaks OTP authentication.

Summary

The default security posture of DirectAccess leaves the internal network open to unauthorized network reconnaissance, and exposes the DirectAccess infrastructure to potential denial-of-service (DoS) attacks. To mitigate these security risks, implement the Citrix NetScaler ADC and enable client certificate authentication.

References

Security Assessment of Microsoft DirectAccess [Overview] – https://www.insinuator.net/2016/04/security-assessment-of-microsoft-directaccess/

Security Assessment of Microsoft DirectAccess [Full Document] – https://www.ernw.de/newsfeed/newsletter-53-may-2016-security-assessment-of-microsoft-directaccess/index.html

Security Assessment of Microsoft DirectAccess Troopers16 Presentation by Ali Hardudi [Video] – https://www.youtube.com/watch?v=wW1x7ow0V9w

Chiron IPv6 Penetration Testing Framework – https://www.insinuator.net/2014/10/chiron-an-all-in-one-ipv6-penetration-testing-framework/

IP-HTTPS specification on MSDN – https://msdn.microsoft.com/en-us/library/dd358571.aspx

Configure F5 BIG-IP to Perform IP-HTTPS Preauthentication – https://directaccess.richardhicks.com/2016/05/23/directaccess-ip-https-preauthentication-using-f5-big-ip/

Configure Windows Server 2012 R2  and Windows Server 2016 to Perform IP-HTTPS Preauthentication – https://directaccess.richardhicks.com/2016/06/13/directaccess-ip-https-preauthentication/

DirectAccess and Windows 10 Better Together

With last week’s release of Windows 10, many organizations who chose to skip Windows 8 are now beginning to deploy Windows 10. To maximize investment in Windows 10, DirectAccess can be leveraged to provide employees with seamless and transparent, always on, secure remote corporate network connectivity. DirectAccess has been around for many years, and today the most popular DirectAccess client is Windows 7. However, Windows 10 provides better support for DirectAccess features that enhance performance and availability, while at the same making it easier to implement and support. Windows 10 opens up many new and compelling deployment scenarios for small businesses to large scale enterprises.

Full Support for Geographic Redundancy

Without a doubt the most important DirectAccess feature Windows 10 supports is automatic entry point selection and transparent failover for multisite deployments. DirectAccess multisite deployment provides essential geographic redundancy for organizations with multiple physical locations. Windows 7 has only minimal support for multisite deployment, with clients required to be assigned to a single entry point. Windows 10 clients are aware of all entry points and will intelligently select the closest entry point when establishing a DirectAccess connection. If the entry point becomes unavailable during the connection, Windows 10 clients will transparently connect to another entry point automatically.

Better Scalability and Performance

Windows 10, like Windows 8 before it, includes support for IP-HTTPS null encryption. This feature greatly improves scalability on the DirectAccess server by eliminating the needless double encryption that Windows 7 clients perform. This reduces resource consumption on the server and enables the server to support many more DirectAccess client connections.

DirectAccess and Windows 10 Better Together

Enhanced Supportability

Many will also appreciate Windows 10’s built-in DirectAccess connectivity status indicator. No longer will administrators have to deploy, manage, and maintain additional software to provide this essential functionality.

To access DirectAccess information in Windows 10, press Window Key + I, click Network & Internet, and then click the DirectAccess tab. Here you will find vital details about DirectAccess configuration and status such as connection state, currently connected entry point, and a site selection drop down box (if manual site selection is enabled by an administrator). In addition you can generate and collect log information for troubleshooting purposes.

DirectAccess and Windows 10 Better Together

Native PowerShell Support

Anyone tasked with troubleshooting DirectAccess configuration and connectivity issues will appreciate the native PowerShell integration with DirectAccess in Windows 10. With just a few commands a wealth of information about DirectAccess configuration and connectivity status can be obtained.

Need to quickly determine if a Windows 10 client has been provisioned for DirectAccess successfully?

Get-DAClientExperienceConfiguration

DirectAccess and Windows 10 Better Together

Has the Windows 10 client connected successfully? If not, why?

Get-DAConnectionStatus

DirectAccess and Windows 10 Better Together

Need to identify the Network Location Server (NLS) the client is configured to use?

Get-NCSIPolicyConfiguration

DirectAccess and Windows 10 Better Together

Looking for DirectAccess multisite entry point details and connection status?

Get-DAEntryPointTableItem

DirectAccess and Windows 10 Better Together

PKI Optional (But Recommended)

Finally, when Windows 10 (and Windows 8.x) clients are supported exclusively a Public Key Infrastructure (PKI) is optional. Here instead the Kerberos Proxy is leveraged to perform DirectAccess client authentication, which reduces infrastructure requirements by eliminating the need for a PKI. However, this configuration offers only limited support for DirectAccess features. For example, a PKI is still required if any Windows 7 clients are deployed. Also, PKI is required to support features such as one-time password (OTP) authentication, Microsoft Network Access Protection (NAP) integration, load balancing (integrated or external), force tunneling, and multisite configuration.

DirectAccess and Windows 10 Better Together

For optimum security and maximum deployment flexibility it is recommended that PKI be used to manage certificates for all DirectAccess deployments including those supporting only Windows 8.x and Windows 10 clients.

Summary

DirectAccess and Windows 10 are much better together. Windows 10 provides full support for the geographic load balancing features of DirectAccess and at the same time offers improved scalability and performance. Windows 10 also makes supporting and troubleshooting DirectAccess clients much easier. And for smaller deployments, Windows 10 can lower the barrier to entry for organizations considering DirectAccess by eliminating the need for a full PKI deployment.

Additional Resources

Video: DirectAccess and Windows 10 in Action
DirectAccess and Windows 10 in Education
Implementing DirectAccess with Windows Server 2016 Book
Implementing DirectAccess with Windows Server 2012 R2 Video Training Course
DirectAccess Consulting Services

Configure DirectAccess with OTP Authentication

Updated 6/10/2015: This post was revised to include instructions for enabling OTP support for Windows 7 clients and for configuring OTP on the DirectAccess server using the Remote Access Management console.

Introduction

DirectAccess in Windows Server 2012 R2 provides significantly improved authentication over traditional client-based VPN solutions. When configured to use certificate authentication (a recommended best practice) the DirectAccess client is authenticated using its machine certificate and its Active Directory computer account. Once the client machine has been authenticated, the user is also authenticated via Kerberos against a live domain controller over the existing DirectAccess connection. These multiple authentication steps provide a high level of assurance for DirectAccess-connected clients. If that’s not enough to meet your needs, additional strong user authentication is supported using dynamic One-Time Passwords (OTP).

Drawbacks for DirectAccess with OTP

While OTP provides an additional level of assurance, it does come with a few drawbacks. OTP adds additional complexity and makes troubleshooting more difficult. OTP cannot be configured with force tunneling; the two security features are mutually exclusive. DirectAccess OTP does not support RADIUS challenge-response. For Windows 7 clients, the DirectAccess Connectivity Assistant (DCA) v2.0 must be deployed. In addition, enabling OTP with DirectAccess disables the use of null cipher suites for IP-HTTPS. This can potentially have a negative effect on performance and scalability (more details here). Also, OTP fundamentally breaks the seamless and transparent nature of DirectAccess.

Configuring DirectAccess OTP

OTP for DirectAccess makes use of short-lived certificates for user authentication. Thus, enabling OTP for DirectAccess requires making changes to the internal Public Key Infrastructure (PKI). DirectAccess in Windows Server 2012 R2 can be configured to use the same Certificate Authority (CA) that is used to issue computer certificates to the DirectAccess clients and servers. This differs from DirectAccess with Forefront Unified Access Gateway (UAG) 2010, where a separate, dedicated CA was required.

To configure DirectAccess OTP, follow the instructions below.

OTP Certificate Request Signing Template

Open the Certification Authority management console, right-click Certificate Templates, and then choose Manage. Alternatively you can enter certtmpl.msc in the Start/Run box or search from the Windows Start menu. Right-click the Computer template and choose Duplicate Template. On a Windows Server 2008 or 2008 R2 CA, select Windows Server 2008 Enterprise when prompted for the duplicate certificate template version.

Configure DirectAccess with OTP Authentication

On a Windows Server 2012 or 2012 R2 CA, select Compatibility tab and then select Windows Server 2008 R2 for the Certification Authority and Windows 7/Windows Server 2008 R2 for the Certificate recipient.

Configure DirectAccess with OTP Authentication

Select the General tab and provide a descriptive name for the Template Display Name. Specify a validity period of 2 days and a renewal period of 1 day.

Configure DirectAccess with OTP Authentication

Select the Security tab and click Add. Click Object Types and then select Computers and click Ok. Enter the names of each DirectAccess server separated by semicolons and click Check Names. Click Ok when finished. For each DirectAccess server, grant Read, Enroll, and Autoenroll permissions. Select Authenticated Users and remove any permissions other than Read. Select Domain Computers and remove the Enroll permission. Select Domain Admins and grant Full Control permission. Do the same for Enterprise Admins.

Configure DirectAccess with OTP Authentication

Select the Subject Name tab and choose the option to Build from this Active Directory information. Select DNS name in the Subject name format drop-down list and confirm that DNS name is checked under Include this information in alternate subject name.

Configure DirectAccess with OTP Authentication

Select the Extensions tab, highlight Application Policies and click Edit.

Configure DirectAccess with OTP Authentication

Remove all existing application policies and then click Add and then New. Provide a descriptive name for the new application policy and enter 1.3.6.1.4.1.311.81.1.1 for the Object Identifier. Click Ok for all remaining dialog boxes.

Configure DirectAccess with OTP Authentication

OTP Certificate Template

In the Certificate Templates Console, right-click the Smartcard Logon certificate template and choose Duplicate Template. On a Windows Server 2008 or 2008 R2 CA, select Windows Server 2008 Enterprise when prompted for the duplicate certificate template version.

Configure DirectAccess with OTP Authentication

On a Windows Server 2012 or 2012 R2 CA, select the Compatibility tab and then select Windows Server 2008 R2 for the Certification Authority and Windows 7/Windows Server 2008 R2 for the Certificate recipient.

Configure DirectAccess with OTP Authentication

Select the General tab and provide a descriptive name for the Template Display Name. Specify a validity period of 1 hour and a renewal period of 0 hours.

Configure DirectAccess with OTP Authentication

Note: It is not possible to set the validity period to hours on a Windows Server 2003 Certificate Authority (CA). As a workaround, use the Certificate Templates snap-in on another system running Windows 7/Windows Server 2008 R2 or later. Also, if the CA is running Windows Server 2008 R2, the template must be configured to use a Renewal Period of 1 or 2 hours and a Validity Period that is longer but no more than 4 hours.

Select the Security tab, then highlight Authenticated Users and grant Read and Enroll permissions. Select Domain Admins and grant Full Control permission. Do the same for Enterprise Admins.

Configure DirectAccess with OTP Authentication

Select the Subject Name tab and choose the option to Build from this Active Directory information. Select Fully distinguished name in the Subject name format drop-down list and confirm that User principal name (UPN) is checked under Include this information in alternate subject name.

Configure DirectAccess with OTP Authentication

Select the Server tab and choose the option Do not store certificates and requests in the CA database. Clear the checkbox next to Do not include revocation information issued in certificates.

Configure DirectAccess with OTP Authentication

Select the Issuance Requirements tab and set the value for This number of authorized signatures to 1. Confirm that Application Policy is selected from the Policy type required in signature drop-down list and choose the OTP certificate request signing template created previously.

Configure DirectAccess with OTP Authentication

Select the Extensions tab, highlight Application Policies and click Edit. Highlight Client Authentication and click Remove. Ensure that the only application policy listed is Smart Card Logon.

Configure DirectAccess with OTP Authentication

Certificate Authority Configuration

In the Certificate Authority management console, right-click Certificate Templates, choose New, and then Certificate Template to Issue. Highlight both of the certificate templates created previously and click Ok.

Configure DirectAccess with OTP Authentication

Open an elevated command prompt and enter the following command:

certutil.exe -setreg dbflags +DBFLAGS_ENABLEVOLATILEREQUESTS

Configure DirectAccess with OTP Authentication

Restart the Certificate Authority service by right-clicking the CA in the Certificate Authority management console and choosing All Tasks and then Stop Service. Once complete, repeat these steps and choose Start Service.

DirectAccess Server Configuration

In the Remote Access Management console, select DirectAccess and VPN under Configuration in the navigate pane and then click Edit on Step 2 – Remote Access Server. Select Authentication, choose Two-factor authentication (smart card or one-time password (OTP)), and then check the option to Use OTP.

Configure DirectAccess with OTP Authentication

Click Next and then add the RADIUS servers that will be used for OTP authentication. Provide the hostname, FQDN, or IP address of the server, the shared secret, and specify the service port.

Configure DirectAccess with OTP Authentication

Click Next, select the CA server that will be used to issue certificates to DirectAccess clients for OTP authentication, and then click Add.

Click Next, select the CA server that will be used to issue certificates to DirectAccess clients for OTP authentication, and then click Add.

Note: When performing this step you may receive the following error.

No CA servers can be detected, and OTP cannot be configured. Ensure that
servers added to the list are available on each domain controller in the
corporate network.

Configure DirectAccess with OTP Authentication

If this occurs, close out of the Remote Access Management console and install this hotfix.

Click Next and select the certificate templates to be used for the enrollment of certificates that are issued for OTP authentication. Also select a certificate template used to enroll the certificate used by the DirectAccess server to sign OTP certificate enrollment requests.

Configure DirectAccess with OTP Authentication

Click Next and specify whether selected DirectAccess users can authenticate with a user name and password when OTP authentication is disabled. If some users need to be exempted from using OTP, specify the security group as required and click Finish.

Configure DirectAccess with OTP Authentication

Click Edit on Step 3 – Infrastructure Servers. Select Management and add the CA server used for OTP authentication to the list of management servers.

Configure DirectAccess with OTP Authentication

Click Ok and then Finish. Click Finish once more and then apply the changes.

DirectAccess OTP Client Experience

When a DirectAccess client is outside of the corporate network and has established DirectAccess connectivity, users can log on to their machine and access their desktop, but they will not be able to access corporate resources without first providing their OTP.

For Windows 8 clients, swipe in from the right side of the screen or press Window Key + I and click on the active network connection. The DirectAccess Workplace Connection will indicate that action is needed. Clicking on the Workplace Connection will indicate that credentials are needed. Clicking Continue will prompt the user to press Ctrl+Alt+Delete and provide their OTP.

Configure DirectAccess with OTP Authentication

For Windows 7 clients, an alert from the DirectAccess Connectivity Assistant (DCA) in the system tray will indicate that Windows needs your smart card credentials. Clicking on the notification Window will prompt the user to provide their OTP.

Configure DirectAccess with OTP Authentication

Alternatively the user can click on the DCA icon in the system tray and then click Lock and unlock your computer with a smartcard or a one-time password. The user will then press CTRL+ALT+DELETE, choose Other Credentials, select One-time password (OTP), and then provide their OTP.

Configure DirectAccess with OTP Authentication

Summary

Using dynamic, one-time passwords is an effective way to provide the highest level of assurance for remote DirectAccess clients. It does come with some potential drawbacks, so be sure to consider those before implementing OTP.

Configuration Guidance for DirectAccess Security Advisory KB2862152

Introduction

Since Microsoft released security advisory KB2862152, there has been much confusion surrounding where the associated update should be installed, in what deployment scenarios it needs to be installed, and what the best way to configure it is. Recently my colleague and good friend Jason Jones and I worked together to research and answer these questions.

Overview

Microsoft security advisory KB2862152 addresses a vulnerability in IPsec that could allow an attacker to perform a man-in-the-middle attack by spoofing a DirectAccess server to intercept network traffic and potentially capture encrypted domain credentials. The associated update is designed to allow security administrators to configure DirectAccess clients to perform more rigorous validation checks when establishing the DirectAccess IPsec tunnels. It’s important to understand that without additional client-side configuration, this security update does nothing.

Windows 8 Clients

For DirectAccess deployments that use Kerberos authentication (Kerberos Proxy), the update needs to be installed on all Windows 8.x clients. No updates are required for Windows 7 clients as they are not supported using this deployment model. To enforce additional validation checks, configure the registry on the Windows 8.x DirectAccess clients with the IP addresses and Service Principal Name (SPN) of the DirectAccess server as outlined here.

Windows 7 Clients

For DirectAccess deployments that use certificate-based authentication, the update needs to be installed on all Windows 7 clients. No updates are required for Windows 8.x client using this deployment model. To enforce additional validation checks, configure the registry on the Windows 7 DirectAccess clients with the IP addresses and either the fully-qualified domain name (FQDN) of the DirectAccess server (not recommended) or the Object Identifier (OID) of the computer certificated used for IPsec authentication (recommended, with custom OID).

The choice between using FQDN or OID is a challenging one, however. Choosing to validate the DNS name is simple and straightforward, but this information may be known to an attacker, or perhaps discoverable, allowing them to spoof it. In addition, there is a limit of 10 DNS names supported using this method, which can be potentially limiting, especially in large, multi-site deployments. Using the certificate OID is even more problematic, because by default it uses a well-known Server Authentication EKU OID (1.3.6.1.5.5.7.3.1) common to many Microsoft Active Directory Certificate Services (AD CS) certificate templates which, of course, could be spoofed by an attacker even easier.

The most effective implementation of this security update for DirectAccess deployments that use certificate-based authentication is to use the OID option with a certificate configured with a custom OID. Custom OIDs are unique to your organization and will help prevent spoofing by using a unique value that is much harder to guess or determine. The remainder of this article will outline how to configure and deploy a certificate with a custom OID along with implementation details for configuring the appropriate client-side registry settings via group policy to enforce the additional validation checks.

Server Configuration

To implement this, it will require creating and deploying a new certificate template. In the Certificate Services management console, right-click Certificate Templates and choose Manage. Right-click the Computer certificate template and choose Duplicate Template. Select the General tab and give the template a descriptive name.

DirectAccess KB2862152 Implementation Guidance

Select the Extensions tab, highlight Application Policies and click Edit. Click Add and then New, and then provide a descriptive name. Leave the OID as is and click Ok to continue.

DirectAccess KB2862152 Implementation Guidance

Right-click once again on Certificate Templates and choose New and then Certificate Template to Issue. Select the certificate template you just created and click Ok.

DirectAccess KB2862152 Implementation Guidance

Once complete you can request a new certificate for each of your DirectAccess servers using this new template.

DirectAccess KB2862152 Implementation Guidance

After you have successfully installed the computer certificate using this new template, be sure to delete the old computer certificate on each DirectAccess server. No further changes are required on the DirectAccess server.

Note: If you are assigning a computer certificate to the DirectAccess server via group policy auto enrollment, the certificate will be reinstalled again after it is deleted, once group policy refreshes. To avoid this situation you will need to deny access to this GPO to ensure that only a single computer certificate with the custom OID is installed on the DirectAccess server.

Client Configuration

To instruct the client to validate the tunnel endpoint IPv6 address and the OID of the DirectAccess server certificate before initiating IPsec tunnels we’ll need to configure registry settings on our DirectAccess clients. Jason Jones’ article describes which settings need to be made and when, so I won’t duplicate his efforts here. However, it is recommended that you deploy these settings using group policy, which I will cover.

To create a Group Policy Object (GPO) to deploy these registry settings, open the Group Policy Management Console, expand the target domain, right-click Group Policy Objects and select New. Give the new GPO a descriptive name and click Ok. Right-click the newly created GPO and choose Edit. Expand Computer Configuration, Preferences, and Windows Settings. Right-click Registry and choose New and then Registry Item. Select Update for the action and HKEY_LOCAL_MACHINE for the hive. Enter

SYSTEM\CurrentControlSet\Services\IKEEXT\Parameters\IPsecTunnelConfig\AuthIP\Cert

for the Key Path and enter DTE1 for the value. Select REG_MULTI_SZ for the Value Type and in the Value Data enter the IPv6 address of the first DTE. On the next line enter EKU:<OID> and click Ok.

DirectAccess KB2862152 Implementation Guidance

Repeat this procedure for each tunnel endpoint. Finally, highlight the GPO and change the Security Filtering from Authenticated Users to the security group for your DirectAccess clients and link the GPO to the domain.

DirectAccess KB2862152 Implementation Guidance

Exercise extreme caution when creating and implementing these GPOs to enforce additional validation checks. If there’s a typo somewhere or you forget a DTE, you could potentially orphan your DirectAccess clients. I recommend testing your changes by manually adding the registry entries required and then copying/pasting those settings to the GPO in Active Directory when you’re ready to deploy globally. Also, don’t forget that you’ll need to update GPOs each time you add a cluster node or multisite entry point.

DirectAccess Clients and TPM

I’ve been frustrated recently with a number of articles and blog posts I’ve seen indicating Windows 8 DirectAccess clients connecting to a Windows Server 2012 DirectAccess server require a Trusted Platform Module (TPM) and the use of smart cards for authentication. This is a myth, and nothing could be further from the truth. TPM and smart cards are indeed supported (TPM with Windows 8, smart cards with Windows 7 and Windows 8 DirectAccess clients) but they are not explicitly required. For the posts I’ve seen I have asked the authors to correct their statements, and to their credit some of them have. Others, unfortunately, have not. I’m not sure if they are simply misinformed or if they are deliberately misleading their readers to downplay DirectAccess in an effort to sell another VPN solution. Regardless, I am compelled to set the record straight here. So, to be perfectly clear:

TPM is NOT a requirement for DirectAccess clients.

There you have it. Now go out and deploy DirectAccess today!

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