Always On VPN SSTP Security Configuration

Always On VPN SSTP Security Configuration

When using Windows Server Routing and Remote Access Service (RRAS) to terminate Always On VPN client connections, administrators can leverage the Secure Socket Tunneling Protocol (SSTP) VPN protocol for client-based VPN connections. SSTP is a Microsoft proprietary VPN protocol that uses Transport Layer Security (TLS) to secure connections between the client and the VPN gateway. SSTP provides some crucial advantages over IKEv2 in terms of operational reliability. It uses the TCP port 443, the standard HTTPS port, which is universally available and ensures Always On VPN connectivity even behind highly restrictive firewalls.

TLS Certificate

When configuring SSTP, the first thing to consider is the certificate installed on the server. A certificate with an RSA key is most common, but for SSTP, provisioning a certificate with an ECDSA key is recommended for optimal security and performance. See the following two articles regarding SSTP certificate requirements and ECDSA Certificate Signing Request (CSR) creation.

Always On VPN SSL Certificate Requirements for SSTP

Always On VPN ECDSA SSL Certificate Request for SSTP

TLS Configuration

Much like IKEv2, the default TLS security settings for SSTP are less than optimal. However, SSTP can provide excellent security with some additional configuration.

TLS Protocols

There are several deprecated TLS protocols enabled by default in Windows Server. These include SSLv3.0, TLS 1.0, and TLS 1.1. They should be disabled to improve security for TLS. To do this, open an elevated PowerShell window on the VPN server and run the following commands.

New-Item -Path ‘HKLM:\SYSTEM\CurrentControlSet\Control\SecurityProviders\SCHANNEL\Protocols\SSL 3.0\Server\’ -Force

New-ItemProperty -Path ‘HKLM:\SYSTEM\CurrentControlSet\Control\SecurityProviders\SCHANNEL\Protocols\SSL 3.0\Server\’ -Name Enabled -PropertyType DWORD -Value ‘0’

New-Item -Path ‘HKLM:\SYSTEM\CurrentControlSet\Control\SecurityProviders\SCHANNEL\Protocols\TLS 1.0\Server\’ -Force

New-ItemProperty -Path ‘HKLM:\SYSTEM\CurrentControlSet\Control\SecurityProviders\SCHANNEL\Protocols\TLS 1.0\Server\’ -Name Enabled -PropertyType DWORD -Value ‘0’

New-Item -Path ‘HKLM:\SYSTEM\CurrentControlSet\Control\SecurityProviders\SCHANNEL\Protocols\TLS 1.1\Server\’ -Force

New-ItemProperty -Path ‘HKLM:\SYSTEM\CurrentControlSet\Control\SecurityProviders\SCHANNEL\Protocols\TLS 1.1\Server\’ -Name Enabled -PropertyType DWORD -Value ‘0’

Cipher Suites

Many weak TLS cipher suites and enabled by default in Windows Server. To further enhance security and performance, they can be optimized using a tool such as IIS Crypto. For example, consider prioritizing cipher suites that use ECDHE and GCM with ECDSA to improve security. Also, remove ciphers that use AES-256 to enhance scalability and performance.

Note: AES-256 does not provide any additional practical security over AES-128. Details here.

PowerShell Script

I have published a PowerShell script on GitHub that performs security hardening and TLS cipher suite optimization to streamline the configuration TLS on Windows Server RRAS servers. You can download the script here.

Validation Testing

After running the script and restarting the server, visit the SSL Labs Server Test site to validate the configuration. You should receive an “A” rating, as shown here.

Note: An “A” rating is not achievable on Windows Server 2012 or Windows Server 2012 R2 when using an RSA TLS certificate. A TLS certificate using ECDSA is required to receive an “A” rating on these platforms.

Additional Information

Always On VPN SSL/TLS Certificate Requirements for SSTP

Always On VPN ECDSA SSL Certificate Request for SSTP

Qualys SSL Labs Server Test Site

Always On VPN Protocol Recommendations for Windows Server RRAS

Microsoft SSTP Specification on MSDN

Always On VPN SSTP Certificate Binding Error

Always On VPN SSTP Certificate Binding ErrorWhen configuring a Windows Server with the Routing and Remote Access Service (RRAS) role to support Windows 10 Always On VPN connections, the administrator may encounter the following error message when installing or updating the TLS certificate used for Secure Socket Tunneling Protocol (SSTP) connections.

“The thumbprint (cert hash) of the certificate used for Secure Socket Tunneling Protocol (SSTP) is different than the certificate bound to the Web listener (HTTP.sys). Configure SSTP to use the default certificate or the certificate bound to SSL. You can configure web server applications to use the same certificate used by SSTP.”

Always On VPN SSTP Certificate Binding Error

IIS Binding

Most commonly this error can occur if an administrator mistakenly binds a TLS certificate directly in IIS. To resolve this problem, open the IIS management console (inetmgr.exe), navigate to the Default Web Site and click Bindings in the Actions section. Highlight the HTTPS binding and click Remove. Once complete, open an elevated command window and run the iisreset.exe command.

Always On VPN SSTP Certificate Binding Error

Netsh

In some instances, the administrator may find no certificate bindings in the IIS management console. However, a certificate binding may still be present. To confirm, open an elevated command window and run the following command.

netsh.exe http show sslcert

Always On VPN SSTP Certificate Binding Error

Remove existing certificate binding by running the following commands.

netsh.exe http delete sslcert ipport=0.0.0.0:443
netsh.exe http delete sslcert ipport=[::]:443

SSTP Configuration

When configuring SSTP in RRAS for Always On VPN, certificate assignment should always be performed using the Routing and Remote Access management console (rrasmgmt.msc). No changes are required to be made in the IIS management console for SSTP.

Additional Information

Windows 10 Always On VPN SSL Certificate Requirements for SSTP

Windows 10 Always On VPN SSTP Load Balancing with Citrix NetScaler ADC Load Balancer

Windows 10 Always On VPN SSTP Load Balancing with Kemp LoadMaster Load Balancer

Windows 10 Always On VPN SSTP Load Balancing with F5 BIG-IP Load Balancer

Troubleshooting Always On VPN Error 691 and 812 – Part 3

Troubleshooting Always On VPN Error 691 and 812 – Part 2When implementing Windows 10 Always On VPN, administrators may encounter errors 691 or 812 when establishing a VPN connection. There are several different configuration issues that will result in these errors. For example they may occur when TLS 1.0 has been disabled on the RRAS server when installed on servers prior to Windows Server 2016. It can also happen if a user’s Active Directory account is configured to deny dial-in access and the NPS server is not configured to ignore user account dial-in properties. Another scenario that can result in 691/812 errors is when the Active Directory security groups are configured as conditions on the Network Policy Server (NPS) Network Policy. See below for more details.

SSTP and Error 691

When attempting to establish an Always On VPN connection using the Secure Socket Tunneling Protocol (SSTP), administrators may encounter the following error message.

“The remote connection was denied because the user name and password combination you provided is not recognized, or the selected authentication protocol is not permitted on the remote access server.”

Troubleshooting Always On VPN Error 691 and 812 – Part 2

In addition, an error 691 with event ID 20227 from the RasClient source can be found in the Application event log on the client.

“The user <domain\user> dialed a connection named which has failed. The error code returned on failure is 691.”

Troubleshooting Always On VPN Error 691 and 812 – Part 2

IKEv2 and Error 812

When attempting to establish an Always On VPN connection using Internet Key Exchange version 2 (IKEv2), administrators may encounter the following error message.

“The connection as prevented because of a policy configured on your RAS/VPN server. Specifically, the authentication method used by the server to verify your username and password may not match the authentication method configured in your connection profile. Please contact the Administrator of the RAS server and notify them of this error.”

Troubleshooting Always On VPN Error 691 and 812 – Part 2

In addition, an error 812 with event ID 20227 from the RasClient source can be found in the Application event log on the client.

Troubleshooting Always On VPN Error 691 and 812 – Part 2

NPS Event Log

On the NPS server the administrator will find an entry in the application event log with event ID 6273 from the Microsoft Windows security auditing source and the Network Policy Server task category indicating the network policy server denied access to the user. Looking closely at this event log message shows Reason Code 48 and the following reason.

“The connection request did not match any configured network policy.”

Troubleshooting Always On VPN Error 691 and 812 – Part 2Group Membership

As stated earlier, another scenario in which administrators will encounter errors 691 and/or 812 is when the Network Policy on the NPS server is configured incorrectly. Specifically, and administrator may wish to grant access to more than one group but intend for access to be granted to users who are a member of any of them. Conversely, they may wish to require access in all specified groups to gain access to the VPN. Configuring each of these conditions is subtly different, however.

Open the NPS management console on the NPS server and follow the steps below to configure user group conditions correctly for the following scenarios.

Any Group

1. Right-click the Always On VPN network policy and choose Properties.
2. Click on the Conditions tab.
3. Click the Add button.
4. Click User Groups.
5. Click Add.
6. Click Add Groups.
7. Enter the name of the group you want to grant access to.
8. Click Ok.
9. Repeat the steps 6-8 above to specify additional groups.

Troubleshooting Always On VPN Errors 691 and 812

All Groups

1. Right-click the Always On VPN network policy and choose Properties.
2. Click on the Conditions tab.
3. Click the Add button.
4. Click User Groups.
5. Click Add.
6. Click Add Groups.
7. Enter the name of the group you want to grant access to.
8. Click Ok.
9. Repeat steps 3-8 above to specify additional groups (you must go back to the Add button on step 3!).

Troubleshooting Always On VPN Errors 691 and 812

Additional Information

Troubleshooting Always On VPN Error 691 and 812 – Part 1

Troubleshooting Always On VPN Error 691 and 812 – Part 2

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