DirectAccess IP-HTTPS Preauthentication


Introduction

DirectAccess IP-HTTPS PreauthenticationRecently Iā€™ve written about the security challenges with DirectAccess, specifically around the use of theĀ 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. Iā€™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, thisĀ change isĀ incompatible with one-time passwords (OTP)Ā  and should not be performed if strong user authentication is enabled.Ā 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 configuringĀ the Citrix NetScalerĀ 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 PKIā€™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.

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