All posts tagged NDES

Windows Server 2016 End of Life January 2027: Plan Your AD CS Migration Now

Happy New Year, everyone! As the calendar rolls over to 2026, it’s time to start planning the migration of workloads hosted on Windows Server 2016. Mainstream support ended for Windows Server 2016 on January 11, 2022, after which it entered extended support. However, extended support for Windows Server 2016 ends on January 12, 2027, at which point it will be end of life and no longer supported. Running production workloads on Windows Server 2016 beyond this date exposes organizations to significant security risk, as it no longer receives security updates, leaving these systems vulnerable to exploits.

Active Directory Certificate Services

Many organizations are still running critical infrastructure on Windows Server 2016. Administrators often delay upgrading Microsoft Active Directory Certificate Services (AD CS) due to its complexity. However, a well-planned AD CS migration not only reduces risk but also provides an opportunity to modernize cryptography, certificate templates, and operational practices.

Certificate Authorities

Administrators must carefully migrate Certificate Authorities (CAs) running on Windows Server 2016 to minimize downtime. In environments where ongoing CA maintenance has been limited, migrating the CA database can be especially challenging. If the CA is installed on a domain controller, now is a good time to consider separating these services to ensure reliable operation. Also, it’s a good idea to evaluate the CA’s configuration and security posture during migration to enhance security and improve service resilience.

NDES Servers

Microsoft Network Device Enrollment Services (NDES) servers, commonly deployed to facilitate certificate enrollment via Microsoft Intune, pose a unique challenge during migration. Unfortunately, configuring NDES is exceedingly complex and error-prone. NDES relies on a delicate combination of specialized IIS configuration, AD service accounts, custom certificate templates, and CA permissions, making even minor changes risky without proper planning. Not surprisingly, administrators are often hesitant to touch these systems as they are notoriously difficult to troubleshoot when problems arise.

Pro Tip: We spend an entire day covering NDES configuration in the Mastering Enterprise PKI Certificates with Microsoft Intune training course. The next session is March 10-12, 2026. Register now!

Intune Certificate Connectors

Don’t overlook Windows Server 2016 servers with the Intune Certificate Connector installed. Fortunately, this is one of the more manageable workloads to migrate. All that’s required is to install new connectors on supported servers and delete the old ones.

Summary

With extended support for Windows Server 2016 ending on January 12, 2027, organizations running production workloads—especially critical infrastructure such as Active Directory Certificate Services (AD CS), Certificate Authorities (CAs), and NDES servers—face significant security risks from unpatched vulnerabilities once the OS reaches end-of-life. Careful migration planning to newer versions such as Windows Server 2022 or 2025 is essential to minimize downtime, improve security posture, and ensure long-term resilience.

Start Planning Now

Don’t leave these mission-critical infrastructure services to the last minute! Begin planning your migration today. If you’d like expert guidance, I have many years of experience migrating these workloads. I have developed specialized tools and techniques to ensure a smooth, secure, and successful transition. Fill out the form below to schedule a free one-hour consultation to assess your Windows Server 2016 AD CS workloads, identify migration risks, and outline next steps.

Additional Information

Windows Server 2016 Lifecycle Policy

PKI Fundamentals with Microsoft Active Directory Certificate Services (AD CS) Online Training Course

Mastering Enterprise PKI Certificates with Microsoft Intune Online Training Course

Intune PKCS and SCEP Certificate Validity Period

With the recent announcement of drastically reduced certificate lifetimes for public TLS certificates, there has been much discussion about certificate lifetimes for private certification authorities (CAs) like Microsoft Active Directory Certificate Services (AD CS). Most commonly, AD CS certificates are issued with a one-year validity period. However, as I’ve discussed in the past, there’s good reason to consider shorter lifetimes in many scenarios. Reducing certificate lifetimes is a growing trend to enhance security, but it poses challenges for private CAs like AD CS. This post explains how to manage shorter certificate lifetimes in Intune using PKCS and SCEP.

AD CS Template

With AD CS, the administrator defines the certificate lifetime by setting the validity period value when creating the certificate template in Active Directory (AD), as shown here.

All certificates issued using this template will be valid for one year from the date of issuance.

Note: The only exception would be if the issuing CA’s certificate were due to expire before the one-year expiration date. In that case, the certificate would be valid until the CA certificate expires.

Intune PKCS and SCEP

When issuing certificates with Intune using either PKCS or SCEP, administrators deploy an Intune enrollment certificate template in AD that Intune uses for user and device certificate enrollment. While the Intune enrollment certificate template defines the default validity period, Intune also allows administrators to specify a desired validity period in the PKCS or SCEP policy settings, as shown here.

Intune Validity Period and AD CS

Although Intune provides the ability to define the validity period on the PKCS or SCEP policy, AD CS does not honor this setting unless explicitly configured to do so. Instead, it defaults to the period defined in the certificate template. Using the example above, the administrator defined a validity period of 1 month. However, since the Intune enrollment certificate template’s validity period was set to one year, a certificate valid for one year will be issued.

Override Template Settings

Fortunately, there is a way to override this default behavior. On the issuing CA where the Intune enrollment certificate template is published, open an elevated PowerShell command window and run the following command.

certutil.exe -setreg Policy\EditFlags +EDITF_ATTRIBUTEENDDATE

Once complete, run the following PowerShell command to restart the CA service.

Restart-Service -Name CertSvc -PassThru

After making this change, administrators can define a shorter certificate validity period than specified on the template using Intune PKCS and SCEP policies.

Note: For security reasons, this setting only allows requests that are shorter than the template’s defined validity period. You cannot request a certificate with a validity period that is longer than the template allows.

Summary

By enabling the EDITF_ATTRIBUTEENDDATE flag on your issuing CA, you gain flexibility to tailor certificate validity periods per use case—while still enforcing a maximum validity via the AD Intune certificate enrollment template. Flexible certificate validity periods are especially valuable in environments that are moving toward short-lived certificates for improved security posture.

Additional Information

TLS Certificate Lifetimes Will Officially Reduce to 47 Days

Always On VPN SSTP and 47-Day TLS Certificates

The Case for Short-Lived Certificates in Enterprise Environments

Mastering Certificates with Microsoft Intune – Live Online Training

Always On VPN Authentication Failure After February 2025 Security Update

Microsoft introduced changes to Windows domain controllers in the February 2025 security update that may result in authentication failures for Always On VPN user tunnel connections. If you suddenly find that all your Always On VPN user tunnel connections fail, additional changes may be required to resolve the issue.

Authentication Failure

Administrators may find that Always On VPN connections fail after applying the February 2025 Microsoft security updates. Specifically, users may receive the following warning message.

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

Error 853

Administrators will also find a corresponding event log entry with event ID 20227 from the RasClient source with the following error message.

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

NPS Events

The event log on the NPS server will also record event ID 6273 from the Microsoft Windows security auditing source with the following error message.

“Network Policy Server denied access to a user.”

The authentication details of the event include Reason Code 16 with the following reason.

“Authentication failed due to a user credentials mismatch. Either the user name provided does not map to an existing user account or the password was incorrect.”

DC Events

If the issue is related to changes implemented to domain controllers in the February 2025 security update, administrators will also find a corresponding event log entry on a domain controller with event ID 39 from the Kerberos-Key-Distribution-Center source with the following error message.

“The Key Distribution Center (KDC) encountered a user certificate that was valid but could not be mapped to a user in a secure way (such as via explicit mapping, key trust mapping, or a SID). Such certificates should either be replaced or mapped directly to the user via explicit mapping.”

Root Cause

The above conditions indicate that a user attempted to authenticate to the VPN with a certificate that was not strongly mapped. Most likely, the certificate was issued using Microsoft Intune with SCEP or PKCS. This results from changes made to domain controllers in the February 2025 security update that requires certificates used for Active Directory authentication to be strongly mapped. Until now, domain controllers allowed access and only logged an event in the event log when a certificate did not include strong certificate mapping. The February 2025 security update now enforces strong certificate mapping, and authentication requests will fail without it.

Resolution

Administrators must issue new certificates that are strongly mapped to resolve this issue. For certificates issued with PKCS, changes are required on the Intune Certificate Connector server before re-issuing. For certificates issued with SCEP, changes to the device configuration policy are required. See the post Strong Certificate Mapping for Intune PKCS and SCEP Certificates for more details.

Workaround

Re-issuing certificates takes time. To restore connectivity immediately, administrators can implement the following registry settings on all domain controllers to switch back to audit mode and allow authentication without strong certificate mapping.

Key: HKLM:\SYSTEM\CurrentControlSet\Services\Kdc
Name: StrongCertificateBindingEnforcement
Type: DWORD
Value: 1

I recommend deploying this setting via GPO assigned to the Domain Controllers OU. However, you can also implement this change using PowerShell if necessary.

New-ItemProperty -Path ‘HKLM:\SYSTEM\CurrentControlSet\Services\Kdc’ -Name ‘StrongCertificateBindingEnforcement’ -PropertyType DWORD -Value 1 -Force

Additional Information

Strong Certificate Mapping for Intune PKCS and SCEP Certificates

Strong Certificate Mapping Enforcement February 2025

Certificate-Based Authentication Changes and Always On VPN

Intune Strong Certificate Mapping Error

Strong Certificate Mapping Error with PKCS

2 Comments

by Richard M. Hicks on February 14, 2025 • Permalink

Posted in Active Directory, Active Directory Certificate Services, AD CS, ADCS, administration, Always On VPN, AOVPN, authentication, Azure VPN, Certificate Authentication, Certificate Authority, Certificate Connector for Intune, Certificate Services, Certificate-Based Authentication, certificates, Cloud PKI, Deployment, Device Management, Enterprise, enterprise mobility, Infrastructure, InTune, Intune Certificate Connector, Intune PFX Connector, Kerberos, MDM, MEM, Microsoft, Microsoft Endpoint Manager, Microsoft Intune, Mobile Device Management, Mobility, Network Device Enrollment Service, Network Device Enrollment Services, network policy server, NPS, Operational Support, PEAP, PFX Connector, PKCS, PKI, PowerShell, Protected EAP, public key infrastructure, Remote Access, SCEP, Security, Simple Certificate Enrollment Protocol, systems management, troubleshooting, Update, user tunnel, VPN, Windows 10, Windows 11

Posted by Richard M. Hicks on February 14, 2025

https://directaccess.richardhicks.com/2025/02/14/always-on-vpn-authentication-failure-after-february-2025-security-update/

Richard M. Hicks Consulting, Inc.

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All posts tagged NDES

Windows Server 2016 End of Life January 2027: Plan Your AD CS Migration Now