Always On VPN Security Updates August 2024

Today is the second Tuesday of the month, so Windows Server administrators everywhere know what that means – it’s Update Tuesday! For Always On VPN administrators in particular there are a few security updates that affect Windows Server Routing and Remote Access (RRAS), which is a popular VPN server used to support Always On VPN implementations. While many of these updates address Remote Code Execution vulnerabilities, non are considered critical.

RRAS Updates

This month there are six vulnerabilities disclosed affecting Windows Server RRAS.

CVE-2024-38120 – Windows RRAS Remote Code Execution Vulnerability (Important)

CVE-2024-38121 – Windows RRAS Remote Code Execution Vulnerability (Important)

CVE-2024-38128 – Windows RRAS Remote Code Execution Vulnerability (Important)

CVE-2024-38130 – Windows RRAS Remote Code Execution Vulnerability (Important)

CVE-2024-38154 – Windows RRAS Remote Code Execution Vulnerability (Important)

CVE-2024-38214 – Windows RRAS Remote Code Execution Vulnerability (Important)

Additional Updates

In addition to the updates addressing vulnerabilities in Windows Server RRAS, there are also updates available for the Windows Network Address Translation (NAT), Windows Transport Layer Security (TLS), and Windows IP Routing Management snapin that could potentially impact Always On VPN deployments.

Recommendations

None of the security vulnerabilities disclosed this month are critical. Although the RRAS vulnerabilities are remote code execution, exploitation is unlikely. However, administrators are encouraged to update their systems as soon as possible.

Additional Information

Microsoft August 2024 Security Updates

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

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.

Considerations

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.

Mitigation

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.

NPS

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.

PowerShell

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

RRAS

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.

CLI

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 = nps.lab.richardhicks.net 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.

Summary

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

What’s New in Absolute Secure Access v13

Recently I wrote about NetMotion Mobility’s acquisition by Absolute Software. Absolute Secure Access (formerly NetMotion Mobility) is an enterprise VPN and Zero Trust Network Access (ZTNA) solution that includes fine-grained policy enforcement to restrict network access based on a wide range of parameters, including IP address, protocol, port, application, time of day, location, and type of network (e.g., wired, Wi-Fi, wireless, etc.), available bandwidth, battery level, and more. It also includes integrated Network Access Control (NAC), which administrators can use to inform access policy decisions based on device security and configuration posture. Now, Absolute has created its first major release since the acquisition – Absolute Secure Access v13.

Secure Web Gateway

Absolute Secure Access is already the most comprehensive and compelling enterprise VPN and ZTNA solution available today. With the release of Absolute Secure Access v13, the solution now includes cloud-based Secure Web Gateway integration, providing administrators with increased visibility and control of web traffic outside the tunnel. Not all web traffic must flow through the secure web gateway. Administrators can use policy to selectively route web traffic through the secure web gateway to meet their requirements.

Enhanced Security

The secure web gateway feature of Absolute Secure Access v13 includes the following enhanced security features.

Web Filtering

The secure web gateway allows administrators to restrict access based on web category (e.g., gambling, malware sites, personal storage, etc.). Administrators can allow or deny access based on risk level or use the destination’s categorization to take policy action to restrict access further or require additional authentication.

TLS Inspection

The secure web gateway can terminate HTTPS (SSL/TLS) sessions to perform traffic inspection and granular content categorization based on the full URL. The TLS inspection certificate is added dynamically to the local computer certificate store.

Virus Scan

The secure web gateway performs malware and virus scans on web content and files, preventing users from downloading malicious software.

Remote Browser Isolation

Remote Browser Isolation (RBI) executes web browsing sessions on a remote, isolated system to prevent potential malware threats. It enhances security by ensuring malicious content is contained and executed away from the user’s device.

Content Disarm and Reconstruction

Content Disarm and Reconstruction (CDR) is a security feature that eliminates dynamic content from downloaded files and guards against zero-day vulnerabilities undetected by antivirus scans.

Data Loss Prevention

Data Loss Prevention (DLP) is designed to prevent sensitive or confidential data from being leaked, accessed, or shared inappropriately, ensuring data security and compliance with regulations.

Policy Enhancements

Absolute Secure Access policies now include actions that can be taken based on information from the secure web gateway. For example, if a user visits a risky category like Malware Sites, additional security features such as antivirus scan, CDR and DLP enforcement, and RBI can be enforced. In addition, administrators can now force reauthentication when users roam between networks.

Summary

Absolute Secure Access v13 significantly upgrades previous versions of Absolute Secure Access and NetMotion Mobility. The security enhancements associated with the new secure web gateway service will tremendously increase an organization’s security posture and eliminate the need for additional web security solutions. Absolute Secure Access has powerful security enforcement technologies with policy and NAC to ensure the highest level of security for today’s mobile workforce.

Learn More

Are you interested in learning more about Absolute Secure Access? Would you like a demonstration of this enterprise VPN and Zero-Trust Network Access solution? Fill out the form below, and we’ll provide more information.