Always On VPN Device Tunnel Issues with April 2024 Security Update

Always On VPN administrators may find that their device tunnel connections no longer connect automatically after applying the April 2024 security updates. The device tunnel connection is optional and only required under specific conditions, so end users may not be immediately impacted. However, administrators should be aware of this issue.

Note: The issues outlined in this post have been resolved with the May 14, 2024, security updates.

Error Messages

When manually establishing an Always On VPN device tunnel connection using rapshone.exe or rasdial.exe, you may receive one of the following error messages.

Rasphone.exe

Error 0x80070057: The parameter is incorrect.

Rasdial.exe

Connecting to <Name of Device Tunnel>…The parameter is incorrect.

Affected Devices

The issue affects all supported versions of Windows with an Always On VPN device tunnel connection configured to require a specific Enhanced Key Usage (EKU) OID. Administrators can run the following PowerShell command to identify this configuration.

Get-VpnConnection -AllUserConnection -Name <Name of Device Tunnel> | Select-Object MachineCertificateEkuFilter

If the output of this PowerShell command returns data, it is affected by this issue.

Workaround

To restore Always On VPN device tunnel functionality on devices with the April 2024 security updates installed, open an elevated PowerShell command window and run the following command.

Set-VpnConnection -AllUserConnection -Name ‘Always On VPN Device Tunnel’ -MachineCertificateEKUFilter $Null

After running this command, the output should now be blank.

Caveat

The problem with implementing the workaround described here is that you likely enabled this configuration to address an issue where the wrong certificate was selected for use with the device tunnel. In this case, the workaround may result in unexpected behavior and may not restore full functionality.

Known Issue Rollback

Currently, Microsoft is aware of the issue and is actively working to resolve it. If you are experiencing this issue, open a support case with Microsoft, and they will provide you with more information and possibly a private Known Issue Rollback (KIR). I will update this post as soon as Microsoft publishes a permanent fix.

Additional Information

Always On VPN Device Tunnel Operation and Best Practices

Always On VPN Device Tunnel Only Deployment Considerations

Considerations for Always On VPN with Azure VPN Gateway and Virtual WAN

Considerations for Always On VPN with Azure VPN Gateway and Virtual WAN

Always On VPN Device Tunnel and Custom Cryptography Native Support Now in Intune

Organizations migrating on-premises applications, data, and infrastructure to the cloud may also consider terminating Always On VPN connections there. Using one of the native Azure VPN services might be compelling at first glance. After all, having an Azure-managed VPN gateway service sounds intuitive. However, some severe limitations exist for using Azure VPN services for Always On VPN deployments.

Azure VPN Gateway

The following are limitations for Always On VPN with Azure VPN gateway.

Authentication Methods

Azure VPN gateway supports both EAP and machine certificate authentication. However, it can only support one authentication method at a time. With only EAP or certificate authentication, administrators must choose between a device or user tunnel. A single Azure VPN gateway cannot support both at the same time. For native Entra ID joined devices, this is not a problem. However, for native on-premises Active Directory or hybrid Entra ID joined devices, this is a problem, as the device tunnel is essential in these scenarios.

Note: Technically speaking, administrators could deploy another Azure VPN gateway to work around this limitation. However, Azure limits VPN gateway deployments to one per virtual network. This requires administrators to deploy a second VPN gateway in a separate virtual network, which then requires virtual network peering to be enabled, complicating the configuration greatly.

SSTP

Although the Azure VPN gateway supports SSTP, it is, unfortunately, a second-class citizen. Today, all SKUs of the Azure VPN gateway are limited to just 128 SSTP connections (256 in active/active mode). There is currently no way to increase this. If more than 256 connections are required, you must use IKEv2.

RADIUS

In addition, there is currently no option to change the default timeout value (30 seconds) for RADIUS authentication requests. This short timeout value presents a challenge when using MFA with the NPS extension or with Azure Conditional Access, as users may be unable to respond to the push notification before the timeout expires, resulting in failed authentication attempts.

In addition, Azure does not support routing traffic to on-premises RADIUS servers over ExpressRoute connections. In this scenario, administrators must route RADIUS traffic to on-premises servers over a site-to-site connection.

Geographic Redundancy

Geographic redundancy using Azure Traffic Manager (or another global server load balancer) with two or more gateways is not supported when using the Azure VPN gateway. Azure manages the certificate used on the gateway, which includes a certificate with the subject name of the individual gateway. There is no option to supply a custom certificate with a global hostname in the subject, which is required to support geographic redundancy. With that, administrators are limited to the redundancy provided natively by the Azure VPN gateway.

IPv6

Azure does not support Azure VPN gateway in a virtual network that includes IPv6 addressing.

Azure Virtual WAN

Azure Virtual WAN includes many of the same limitations as the Azure VPN gateway, in addition to the following.

SSTP

Unlike the Azure VPN gateway, there is no support for SSTP in Azure Virtual WAN.

IPv6

IPv6 is not currently supported at all in Azure Virtual WAN.

Summary

Intuitively, it seems that leveraging native Azure VPN gateway services would be ideal. However, due to the limitations outlined in this article, administrators must decide carefully if any of these prevent adoption in their environment. Although not formally supported, many organizations deploy Windows Server Routing and Remote Access (RRAS) servers in Azure to address these limitations.

Additional Information

Always On VPN Options for Azure Deployments

Always On VPN with Azure Gateway

Always On VPN Device Tunnel with Azure VPN Gateway

Always On VPN and RRAS in Azure

What is Azure VPN Gateway?

What is Azure Virtual WAN?

Always On VPN October 2023 Security Updates

Once again, it’s time to patch! After several quiet months, there are a few crucial updates Always On VPN administrators will want to get deployed soon. Thankfully, the impact of the security updates related to Always On VPN is low this time, as there is only one Remote Code Execution (RCE) vulnerability, and it’s for a legacy protocol that should be in limited use today.

IKEv2

CVE-2023-36726 addresses a security vulnerability in Windows Internet Key Exchange (IKE) that can lead to privilege escalation. An attacker who successfully exploits this vulnerability can elevate privileges to that of the local SYSTEM.

L2TP

This month’s update discloses several Layer Two Tunneling Protocol (L2TP) vulnerabilities. The following CVEs all address a vulnerability where an attacker can send a specially crafted protocol message to a Windows Routing and Remote Access Service (RRAS) server, which could lead to remote code execution on the server.

Mitigation

The impact of the L2TP security vulnerabilities should be minimal in most organizations. L2TP is a legacy VPN protocol not commonly used for Always On VPN. However, misconfiguration can leave vulnerable RRAS servers exposed. Administrators must ensure that inbound UDP port 1723 is not open from the Internet. In addition, L2TP should be disabled on the RRAS server if not in use. See the article on the May 2023 security updates for details.

Additional Information

October 2023 Security Updates