Always On VPN and Blast-RADIUS

Microsoft released an update for the Windows Server Network Policy Server (NPS) to address recently disclosed vulnerabilities in the Remote Access Dial-In User Service (RADIUS) protocol in the July 2024 security updates. RADIUS is an industry-standard authentication protocol widely used for remote access, including Always On VPN. The RADIUS protocol was first introduced in the early 1990s and, unfortunately, still relies on the deprecated MD5 cryptographic hash function. The good news is that this vulnerability does not affect Always On VPN. Read on to learn more.


Blast-RADIUS is an attack on the RADIUS protocol that allows an attacker to alter network authentication packets to gain access to a service relying on RADIUS for authentication by exploiting the weakness of MD5 integrity checks in RADIUS. In the absence other controls, an attacker could alter an authentication response and change the reply from Access-Reject to Access-Accept.


It’s important to note that leveraging this attack is not trivial. It requires local network access, so the attacker must have a presence on the target network to carry out this attack. However, cloud-hosted RADIUS services are inherently more vulnerable. In addition, the attack is mostly academic today because the default timeout for authentication requests is typically short, usually between 5 and 30 seconds. This is not enough time (today) for an attacker to mount the attack. However, this attack could become more feasible if authentication timeouts are increased (sometimes required to support MFA) or if an attacker has access to vast computing resources.

Affected Protocols

Although Blast-RADIUS is a vulnerability in the RADIUS protocol itself, not all authentication protocols are affected. Specifically, this vulnerability affects services leveraging PAP, CHAP, MS-CHAP, and MS-CHAPv2. Extensible Authentication Protocol (EAP) and Protected Extensible Authentication Protocol (PEAP) are not vulnerable to this attack. Since Always On VPN requires EAP authentication, it is not susceptible to this attack.


Microsoft has published guidance in KB5040268 for mitigating Blast-RADIUS attacks on Windows NPS servers. Specifically, administrators are encouraged to enable the Message-Authenticator attribute in Access-Request packets sent by the network access server and to ensure the NPS server requires the Message-Authenticator attribute in any Access-Request messages it receives.

Note: The following changes are not required for Always On VPN or any other workload using EAP-TLS or Protected EAP, as these protocols use TLS natively to protect the authentication exchange.


To configure this setting in the UI, open the NPS management console (nps.msc) and perform the following steps.

  1. Expand RADIUS Clients and Servers.
  2. Highlight RADIUS Clients.
  3. Right-click the RADIUS client to configure and choose Properties.
  4. Select the Advanced tab.
  5. Check the box next to Access-Request messages must contain the Message-Authenticator attribute.


To configure this setting using PowerShell, open an elevated PowerShell command window and run the following command.

Set-NpsRadiusClient -Name <RADIUS client name> -AuthAttributeRequired $True

Additional NPS Settings

Administrators should also run the following commands on their NPS servers to further protect their infrastructure from Blast-RADIUS attacks.

netsh.exe nps set limitproxystate all = enable

netsh.exe nps set requiremsgauth all = enable


When using Windows Server Routing and Remote Access (RRAS) without EAP, ensure the RADIUS server configuration always includes the Message-Authenticator. To configure this setting, open the Routing and Remote Access console (rrasmgmt.msc) on the RRAS server and perform the following steps.

  1. Right-click the VPN server and choose Properties.
  2. Select the Security tab.
  3. Click the Configure button next to the Authentication provider drop-down list.
  4. Highlight the RADIUS server and choose Edit.
  5. Check the box next to Always use message authenticator.

Repeat these steps for any additional configured RADIUS servers.


Administrators can implement this change at the command line by opening an elevated command window and entering the following command.

netsh.exe ras aaaa set authserver name = <name of RADIUS server> signature = enabled

For example:

netsh.exe ras aaaa set authserver name = signature = enabled

New NPS Events

After installing the KB5040268 update on NPS servers, the NPS server will record event ID 4421 from the NPS source after a service start if the RequireMsgAuth or LimitProxyState settings are not configured.

“RequireMsgAuth and/or limitProxyState configuration is in Disable mode. These settings should be configured in Enable mode for security purposes.”

Optional Mitigation

If administrators cannot configure the above settings, consider using IPsec to secure network traffic at the transport layer. IPsec will protect all RADIUS traffic at the network layer to mitigate Blast-RADIUS attacks. Unfortunately, Windows Server NPS does not support TLS or DTLS, so IPsec is your only option.


Always On VPN is not vulnerable to the Blast-RADIUS attack. However, NPS is commonly a shared service in many organizations, and other workloads may use older, vulnerable protocols. Consider implementing the changes detailed in KB5040268 as outlined in above to ensure the integrity of your environment and mitigate these potential attacks.

More Information

Microsoft KB5040268: how to manage Access-Request packets attack vulnerability associated with CVE-2024-3596

RADIUS Protocol Vulnerability Exposes Networks to MitM Attacks

New Blast-RADIUS attack breaks 30-year-old protocol used in networks everywhere

Overview of Microsoft Protected Extensible Authentication Protocol (PEAP)

Always On VPN NPS Auditing and Logging

Microsoft DirectAccess Formally Deprecated

Today, Microsoft has announced the formal deprecation of DirectAccess. Microsoft DirectAccess is a widely deployed enterprise secure remote access solution that provides seamless, transparent, always-on remote network connectivity for managed (domain-joined) Windows clients. First introduced in Windows Server 2008 R2, it’s been a popular solution with many advantages over ordinary VPN technologies of the past.

Windows Server 2012

DirectAccess was almost entirely rewritten in Windows Server 2012. Many of the features and enhancements offered for DirectAccess with the Unified Access Gateway (UAG – a separate product with additional costs) were built into the operating system directly. In addition, Microsoft introduced integrated load balancing and geographic redundancy features.

Demise of DirectAccess

DirectAccess relies heavily on classic on-premises technologies like Active Directory. All DirectAccess servers and clients must be joined to a domain. In addition, all DirectAccess clients must be running the Enterprise edition of Windows. With organizations rapidly adopting cloud services such as Azure and Entra ID, Microsoft began to develop an alternative solution that better integrated with the cloud. That solution is Always On VPN. With that, Microsoft stopped developing DirectAccess after the release of Windows Server 2012 R2. No new features or capabilities have been added to DirectAccess since that time.


We’ve been speculating about the end of life for DirectAccess for quite some time now. However, this formal deprecation announcement from Microsoft is official. It is the end of the road for this technology. To be clear, though, DirectAccess is available today in Windows Server 2022 and Windows 11. DirectAccess will be included in the upcoming release of Windows Server 2025. However, formal deprecation from Microsoft means they will remove DirectAccess components from the next release of the operating system.

What Happens Now?

Organizations should begin formal planning efforts to migrate away from DirectAccess. Here are a few popular solutions to consider.

Always On VPN

Always On VPN is the direct replacement for DirectAccess. It was designed to provide feature parity for DirectAccess, with seamless, transparent, always-on remote network connectivity. However, Always On VPN better integrates with Entra ID and supports conditional access. It does not require domain-joined devices or servers and works well with cloud-native endpoints. Always On VPN is a good choice for organizations that employ hybrid Entra-joined devices.

Entra Private Access

Entra Private Access, part of the Entra Global Secure Access suite, is an identity-centric zero-trust network access (ZTNA) solution from Microsoft. It is in public preview now and has some compelling advantages over traditional VPNs. However, Entra Private Access is not feature complete today. In addition, it is best suited to cloud-native (Entra-joined only) endpoints.

Absolute Secure Access

Absolute Secure Access (formerly NetMotion Mobility) is a premium enterprise remote access solution with many advanced options. It is by far the best solution on the market today. Absolute Secure Access is a software solution that supports zero-trust configuration and includes many features to improve and enhance security, performance, and visibility. In addition, it provides cross-platform support, including Windows, macOS, iOS, and Android operating systems.

Learn More

We have several decades of experience working with secure remote access technologies. We can help you and your organization find the best solution for your needs. Fill out the form below for a free one-hour consultation to discuss your DirectAccess migration strategy today.

Additional Information

Deprecated Features for Windows Client

Always On VPN Security Updates June 2024

The Microsoft security updates for June 2024 have now been published. Reviewing the list of bulletins shows three security updates of importance to Always On VPN administrators. Two affect the Windows Server Routing and Remote Access (RRAS) service, and one affects the Remote Access Connection Manager (RasMan) service. None of the updates are critical this month, which is good news.


The following are the two security updates from this month’s cycle affecting Windows Server RRAS.

CVE-2024-30094 – Windows RRAS Remote Code Execution Vulnerability (Important)

CVE-2024-30095 – Windows RRAS Remote Code Execution Vulnerability (Important)


The following security update affects the Remote Access Connection Manager (RasMan) service on Windows Server systems.

CVE-2024-30069 – Windows Remote Access Connection Manager Information Disclosure Vulnerability (Important)


None of the security vulnerabilities disclosed this month are critical and require local access to the system to take advantage of the exploit. However, administrators should update their systems as soon as possible.

Additional Information

Microsoft June 2024 Security Updates