DirectAccess IP-HTTPS Null Cipher Suites Not Available

DirectAccess IP-HTTPS Null Cipher Suites Not AvailableMicrosoft first introduced support for null cipher suites for the IP-HTTPS IPv6 transition technology in Windows Server 2012, and it is supported for DirectAccess in Windows 8.x and Windows 10 clients. Using null cipher suites for IP-HTTPS eliminates the needless double encryption that occurs when using encrypted cipher suites. DirectAccess is a unique workload where SSL/TLS encryption isn’t really required because the payload being transported in HTTPS is already encrypted.

No Encryption by Design

When supporting Windows 8.x and Windows 10 clients, ensuring null cipher suites (TLS_RSA_WITH_NULL_SHA and TLS_RSA_WITH_NULL_SHA256) are enabled and operational is crucial to providing the highest levels of performance and scalability for the remote access solution. When following implementation best practices, this isn’t really an issue. However, in some cases null cipher suites may be disabled. This will result in reduced scalability and degraded performance for Windows 8.x and Windows 10 clients.

Validating SSL/TLS Configuration

The easiest way to verify that null cipher suites are being offered by the DirectAccess server is to use the Qualys SSL Labs server test site. Ideally you should see a result similar to this.

DirectAccess IP-HTTPS Null Cipher Suites Not AvailableFigure 1. Qualys SSL Labs server test site results for properly configured DirectAccess server.

Don’t be alarmed by the overall rating “F”. That happens because the Qualys test site is designed to test web servers where using null cipher suites would be a serious security issue. As I stated previously, the DirectAccess workload is unique in that its HTTPS payload is already encrypted, so using null cipher suites is acceptable in this scenario.

DirectAccess IP-HTTPS Null Cipher Suites Not AvailableFigure 2. Qualys SSL Labs server test site results for properly configured DirectAccess server showing support for null SSL/TLS cipher suites.

Null Cipher Suites Missing

When performing the Qualys SSL labs server test on a DirectAccess server, an overall rating of “A” is not desirable and indicates the DirectAccess server is misconfigured. This is caused by the lack of support for null cipher suites.

DirectAccess IP-HTTPS Null Cipher Suites Not AvailableFigure 3. Qualys SSL Labs server test site results for misconfigured DirectAccess server.

Common Causes

Null cipher suites for SSL and TLS can be disabled for a variety of reasons. Below are some of the most common causes for the lack of support for null cipher suites for DirectAccess.

Self-Signed Certificates – Using the Getting Started Wizard (simplified deployment) will configure DirectAccess using a self-signed certificate for IP-HTTPS. Using a self-signed certificate is discouraged for numerous reasons, most importantly because it disables support for null cipher suites.

Security Hardening – Security administrators may proactively disable support for null cipher suites in a misguided effort to “improve security” for DirectAccess. While this is acceptable and recommended on a web server, it is not advisable to disable null cipher suites on a DirectAccess server.

SSL Certificate Signing Algorithm – Using an SSL certificate signed with an Elliptical Curve (EC) key as opposed to an RSA key will result in the loss of support for null cipher suites for IP-HTTPS. High security/assurance certificates signed with EC keys are not recommended for use on DirectAccess servers and should be avoided if possible.

DirectAccess Configuration Options – Enabling One-Time Password (OTP) authentication on the DirectAccess server will also result in a loss of support for null cipher suites. Also, adding additional roles to the DirectAccess server such as client-based VPN or the Web Application Proxy (WAP) can also result in null cipher suites being disabled.

Summary

Null cipher suites are implemented by design on DirectAccess servers to enhance performance for Windows 8.x and Windows 10 clients and improve overall scalability for the implementation. They eliminate the pointless double encryption of DirectAccess communication, which itself is already encrypted. For optimal performance and scalability, be sure to follow implementation best practices and use a PKI-managed (public or private) SSL certificate signed with an RSA key (SHA-256 recommended). Resist the urge to “harden” the DirectAccess server by disabling support for null cipher suites, and avoid the use of SSL certificates signed with EC keys. In addition, carefully consider DirectAccess deployment options such as OTP authentication and consider deploying roles such as VPN and WAP on a separate server.

Additional Information

DirectAccess IP-HTTPS SSL and TLS Insecure Cipher Suites

DirectAccess IP-HTTPS Null Encryption and SSTP VPN

DirectAccess and FIPS Compliant Algorithms for Encryption

SSL Certificate Considerations for DirectAccess IP-HTTPS 

 

 

DirectAccess in Windows Server 2016 at Microsoft Ignite 2016

I’m pleased to announce that I will be delivering a community theater session at this year’s Microsoft ignite conference in Atlanta, GA. The session, THR2136 in the session catalog, is scheduled for Thursday, September 29 at 12:40PM. This is a level 200 talk where I’ll be providing a high-level overview of all remote access technologies in Windows Server 2016, including DirectAccess, client-based VPN, and Web Application Proxy (WAP). I’ll be focusing on what’s new in each of these technologies and demonstrating how each solution applies in different use cases.

DirectAccess in Windows Server 2016 at Microsoft Ignite 2016

In addition to the session, I’ll be spending time with the folks from PointSharp and Pluralsight in their respective booths too, answering questions and providing demonstrations. I hope to have copies of my new DirectAccess book to sign as well. Be sure to follow me on Twitter for up-do-date details. Hope to see you at the conference!

New Pluralsight Windows Server 2012 R2 DirectAccess, VPN, and WAP Video Training Course

Pluralsight IT Pro and Developer TrainingI’m very excited to announce that my latest video training course is now available on Pluralsight! Recently I had the opportunity record a “Play-by-Play” session entitled Secure Remote Access with Windows Server 2012 R2. In this course I cover all aspects of the Unified Remote Access role in Windows Server 2012 R2 including DirectAccess, client-based remote access VPN, site-to-site VPN, and the Web Application Proxy (WAP). This training course differs from some of the other DirectAccess video training content I’ve developed in the past. This course is much less formal, and takes a casual, conversational approach to delivering the content. Many scenarios are presented and discussed, and of course there is plenty of practical demonstration as well. I think you’ll really like this unique format.

Pluralsight IT Pro and Developer Training

Pluralsight video training is available as a monthly subscription. If you don’t already have a Pluralsight account, you can sign up immediately and get a 10-day free trial. In addition to viewing my new course, be sure to browse their amazing video training course catalog. The amount and quality of content they have is astounding. You’ll find my DirectAccess with Windows Server 2012 R2 course there, along with many others. I’m confident you’ll find the service a tremendous value. Get started now!

DirectAccess and the TLS Logjam Attack

Another critical flaw affecting Transport Layer Security (TLS) was discovered recently that could put some organizations at risk. The “Logjam” attack exploits a weakness in how the Diffie-Hellman key exchange is used. An attacker, acting as a man-in-the-middle, can potentially force a downgrade of the TLS connection, resulting in the use of weak cryptography. The Qualys SSL Labs SSL Server Test has been updated to identify this vulnerability. When testing a DirectAccess server you will receive the following warning message.

“This server supports weak Diffie-Hellman (DH) key exchange parameters. Grade capped to B.”

DirectAccess and the Logjam Attack

DirectAccess leverages SSL and TLS as part of the IP-HTTPS IPv6 transition protocol, which is used to tunnel IPv6 packets over the IPv4 Internet. These IPv6 packets are encrypted using IPsec. If an attacker were to break the SSL/TLS connection they would gain nothing. Because of this, a dedicated DirectAccess server is unaffected by the Logjam attack. Mitigating it would provide no additional protection, so you can safely ignore the warning about weak DH key exchange parameters being supported.

However, if DirectAccess has been configured to use one-time password (OTP) authentication, the client-based VPN role has been enabled and configured, or the Web Application Proxy (WAP) role has been installed on the DirectAccess server, then the Logjam attack represents a serious risk and should be mitigated. Also, in some cases it may be desirable to make this change on a dedicated DirectAccess server just to prevent an audit finding and avoid having to explain why the DirectAccess workload would be unaffected by this attack.

To mitigate this vulnerability it will be necessary to remove support for cipher suites that use the Diffie-Hellman key exchange protocol on the DirectAccess server. This is accomplished by opening the Local Group Policy Editor (gpedit.msc) on the DirectAccess server and expanding Computer Configuration, Administrative Templates, and Network. Select SSL Configuration Settings and then double-click SSL Cipher Suite Order. Select Enabled and then replace the default list of cipher suites with the following list.

TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384_P384
TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256_P256
TLS_ECDHE_ECDSA_WITH_AES_256_CBC_SHA384_P384
TLS_ECDHE_ECDSA_WITH_AES_128_CBC_SHA256_P256
TLS_ECDHE_ECDSA_WITH_AES_256_CBC_SHA_P384
TLS_ECDHE_ECDSA_WITH_AES_256_CBC_SHA_P256
TLS_ECDHE_ECDSA_WITH_AES_128_CBC_SHA_P384
TLS_ECDHE_ECDSA_WITH_AES_128_CBC_SHA_P256
TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA_P384
TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA_P256
TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256_P384
TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256_P256
TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA_P384
TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA_P256
TLS_RSA_WITH_AES_256_CBC_SHA256
TLS_RSA_WITH_AES_256_CBC_SHA
TLS_RSA_WITH_AES_128_CBC_SHA256
TLS_RSA_WITH_AES_128_CBC_SHA
TLS_RSA_WITH_NULL_SHA256
TLS_RSA_WITH_NULL_SHA

DirectAccess and the Logjam Attack

Once complete, restart the DirectAccess server. The Qualys SSL Labs server test should no longer give a warning about the use of weak Diffie-Hellman keys. In addition, this reordering and optimization of cipher suites will also improve the protocol support and key exchange scores, as shown here.

DirectAccess and the Logjam Attack

As a reminder, and overall rating of “F” is expected when testing a dedicated DirectAccess server. By design, DirectAccess provides support for null cipher suites to improve scalability and performance for Windows 8.x and later DirectAccess clients. More details here.

DirectAccess Load Balancing and Multisite Configuration Options Unavailable

Looking for more information about DirectAccess load balancing? See my post entitled DirectAccess Deployment Guide for Kemp LoadMaster Load Balancers.

DirectAccess in Windows Server 2012 R2 supports load balancing and multisite configuration options to provide both local and geographic redundancy, respectively. To configure either of these options, open the Remote Access Management console, expand Configuration in the navigation tree, highlight DirectAccess and VPN, and then select either Enable Multisite or Enable Load Balancing in the Tasks pane.

DirectAccess Load Balancing and Multisite Configuration Options Unavailable

Depending on your configuration you may encounter a scenario in which these features do not appear in the Remote Access Management console.

DirectAccess Load Balancing and Multisite Configuration Options Unavailable

This occurs when the Web Application Proxy (WAP) role is installed on the DirectAccess server. Although this is a supported configuration, enabling load balancing or multisite on a DirectAccess server with WAP installed requires additional configuration. Specifically, load balancing and/or multisite must be configured before installing the WAP role.

To restore support for load balancing and multisite configuration options, remove the WAP role using the GUI or with the Uninstall-WindowsFeature Web-Application-Proxy PowerShell command.

TechDays San Francisco 2014

I’m very excited to announce that I’ll be presenting at TechDays in San Francisco on June 5 & 6, 2014! I’ll be delivering a session on cloud and remote access networking in Windows Server 2012 R2. Not only will this session include DirectAccess, but I will also be covering client-based VPN, site-to-site VPN, and the new Web Application Proxy role. If time permits, I might even sneak in some details about Workplace Join and Work Folders. Registration is open now, so sign up soon. Hope to see you there!

TechDays San Francisco 2014

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