All posts in category Protected EAP

Always On VPN NPS and PEAP Vulnerabilities

The February 2023 security updates for Windows Server address multiple vulnerabilities that affect Microsoft Always On VPN administrators. This latest update addresses multiple critical and important vulnerabilities in the Network Policy Server (NPS), commonly used to perform RADIUS authentication for Always On VPN servers. Specifically, there are several Remote Code Execution (RCE) and Denial of Service (DoS) vulnerabilities with Protected Extensible Authentication Protocol (PEAP). PEAP with user authentication certificates is the authentication protocol of choice for Always On VPN user tunnel authentication.

Vulnerabilities

The following is a list of vulnerabilities in PEAP addressed in the February 2023 security update.

  • CVE-2023-21689 – Microsoft PEAP Remote Code Execution Vulnerability (critical)
  • CVE-2023-21690 – Microsoft PEAP Remote Code Execution Vulnerability (critical)
  • CVE-2023-21691 – Microsoft PEAP Information Disclosure vulnerability (important)
  • CVE-2023-21692 – Microsoft PEAP Remote Code Execution Vulnerability (critical)
  • CVE-2023-21695 – Microsoft PEAP Remote Code Execution Vulnerability (important)
  • CVE-2023-21701 – Microsoft PEAP Denial of Service Vulnerability (important)

Mitigation

Unauthenticated attackers can exploit the RCE vulnerabilities in PEAP on Microsoft Windows NPS servers. However, NPS servers should not be exposed directly to the Internet and would require an attacker to have access to the internal network already. However, administrators are advised to apply this update to their NPS servers as soon as possible. In addition, organizations that deploy the NPS role on enterprise domain controllers should update immediately.

Additional Information

February 2023 Update for Windows Server 2022 (KB5022842)

February 2023 Update for Windows Server 2019 (KB022840)

February 2023 Update for Windows Server 2016 (KB5022838)

2 Comments
by Richard M. Hicks on February 16, 2023  •  Permalink
Posted in Active Directory, administration, Always On VPN, AOVPN, authentication, certificates, Cryptography, Device Management, EAP, Encryption, Enterprise, enterprise mobility, extensible authentication protocol, Hotfix, Infrastructure, Microsoft, Mobility, network policy server, NPS, Operational Support, PEAP, Protected EAP, Remote Access, Security, Update, user tunnel, VPN, Vulnerability, Windows Server 2016, Windows Server 2019, Windows Server 2022
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Posted by Richard M. Hicks on February 16, 2023

https://directaccess.richardhicks.com/2023/02/16/always-on-vpn-nps-and-peap-vulnerabilities/

Always On VPN Error 853 on Windows 11

Recently I did some validation testing with Always On VPN on Windows 11, and I’m happy to report that everything seems to work without issue. However, a few readers have reported 853 errors when establishing an Always On VPN connection after upgrading to Windows 11.

Can’t Connect

After upgrading to Windows 11, an Always On VPN connection may fail with the following error message.

“The remote access connection completed, but authentication failed because the certificate that authenticates the client to the server is not valid. Ensure the certificate used for authentication is valid.”

Error 853

In addition, the Application event log records an event ID 20227 from the RasClient source that includes the following message.

“The user <username> dialed a connection name <connection name> which has failed. The error code returned on failure is 853.”

Server Identity

This error will occur when using Protected Extensible Authentication Protocol (PEAP) authentication. Specifically, it can happen when the option to verify NPS server validity by its certificate is selected, and an explicit list of NPS servers is defined, as shown here.

Case Sensitive

In this specific scenario, Windows 11 now appears to be case-sensitive when it compares the NPS server name entered in the NPS configuration to the Subject Name on the certificate returned by the server. For example, if the Subject Name (or Subject Alternative Name, if present) entry on the NPS server certificate is nps.lab.richardhicks.net, using NPS.lab.richardhicks.net will not match and return an 853 error.

Windows 11

Case matching when validating the NPS server certificate is a change in behavior from Windows 10. Before Windows 11, this comparison was case-insensitive, and any combination of case would match if the entire hostname matched. Going forward, it appears Microsoft has also decided to require case matching to validate the server certificate.

Recommendations

Administrators should look carefully at the server certificate issued to the NPS server and ensure their client configuration accurately reflects the hostname in a case-sensitive manner to ensure a smooth migration from Windows 10 to Windows 11.

Additional Information

Troubleshooting Windows 10 Always On VPN Error 853

Windows 10 Always On VPN Network Policy Server (NPS) Load Balancing

22 Comments
by Richard M. Hicks on September 23, 2021  •  Permalink
Posted in Always On VPN, AOVPN, authentication, certificates, EAP, Enterprise, enterprise mobility, extensible authentication protocol, Mobility, Name Resolution, network policy server, NPS, PEAP, Protected EAP, Remote Access, Security, troubleshooting, VPN, Windows 11
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Posted by Richard M. Hicks on September 23, 2021

https://directaccess.richardhicks.com/2021/09/23/always-on-vpn-error-853-on-windows-11/

Always On VPN Short Name Access Failure

Using Microsoft Endpoint Manager (Intune), administrators can provision Always On VPN to devices that are Azure AD joined only. Users accessing on-premises resources from these devices can still use seamless single sign-on, making this deployment option popular for organizations moving to the cloud.

Short Names

After deploying Always On VPN to Windows 10 devices that are Azure AD joined only and configured to use client certificate authentication, administrators may find that users cannot access on-premises resources by their short name, such as \\app1. The connection fails and returns the following error message.

“Windows can’t find <servername/sharename>. Check the spelling and try again.”

FQDN

Interestingly, on-premises resources are accessible using their fully qualified domain name (FQDN), such as \\app1.corp.example.net.

Troubleshooting

Testing name resolution using the short name works as expected, and the resource is reachable at the network layer, as shown here.

Workaround

This issue is related to how Windows performs authentication when connected via VPN. To resolve this issue, edit the rasphone.pbk file and change the value of UseRasCredentials to 0. Rasphone.pbk can be found in the $env:AppData\Microsoft\Network\Connections\Pbk folder.

After updating this setting, restart the VPN connection for the change to take effect.

Proactive Remediations

While helpful for testing, editing rasphone.pbk manually obviously does not scale well. To address this, consider using Intune Proactive Remediations. Intune Proactive Remediations allows administrators to deploy detection and remediation PowerShell scripts to monitor specific settings and update them if or when they change. Proactive Remediations will ensure the setting is applied consistently across all managed endpoints.

GitHub Repository

I have created a new GitHub repository dedicated to PowerShell scripts for Endpoint Manager Proactive Remediations for Always On VPN. There you will find detection and remediation scripts for the UseRasCredentials settings change described in this article.

PowerShell

Administrators can also implement this setting by running the following PowerShell command.

Set-ItemProperty -Path ‘HKLM:\SYSTEM\CurrentControlSet\Control\Lsa’ -Name DisableDomainCreds -Value 1

Group Policy

Another option for implementing this setting is by enabling the following Active Directory Group Policy setting.

Computer Configuration > Windows Settings > Security Settings > Local Policies > Security Options > Network access: Do not allow storage of passwords and credentials for network authentication

Additional Information

Always On VPN Endpoint Manager Proactive Remediation Scripts on GitHub

Endpoint Manager Proactive Remediations Tutorial

21 Comments
by Richard M. Hicks on September 20, 2021  •  Permalink
Posted in Always On VPN, AOVPN, authentication, Azure Active Directory, Azure AD, Azure AD Join, certificates, cloud, DNS, EAP, Endpoint Manager, Enterprise, enterprise mobility, extensible authentication protocol, GitHub, InTune, MEM, MEMCM, Microsoft Endpoint Manager, Microsoft Intune, Mobility, Name Resolution, Operational Support, PEAP, PowerShell, Protected EAP, public cloud, Remote Access, SCCM, System Center Configuration Manager, systems management, troubleshooting, user tunnel, VPN, Windows 10
Tagged , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , ,

Posted by Richard M. Hicks on September 20, 2021

https://directaccess.richardhicks.com/2021/09/20/always-on-vpn-short-name-access-failure/

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