Microsoft recently introduced Entra Private Access, an identity-centric Zero Trust Network Access (ZTNA) solution to provide secure remote access to on-premises resources. With Entra Private Access, administrators can leverage Entra Conditional Access to enforce policy-based access control for network access. However, Entra Private Access isn’t for everyone. It does not provide full feature parity with Always On VPN, and there are also licensing considerations. However, for those organizations using Always On VPN, the good news is that you can integrate Entra Conditional Access with Always On VPN today to gain some of the security benefits it provides.
Conditional Access
Microsoft Entra Conditional Access is a security feature that enables administrators to create and enforce policies that specify how users can access resources. In the specific case of Always On VPN, conditional access is critical to ensuring legitimate access to authenticated users on authorized devices.
Signals
Conditional access policies use a wide variety of signals for policy enforcement, such as:
User Identity: Who is making this access request?
User Properties: Is this user a member of a specific group?
Location: Where is this access request originating?
Device Management: Is this device joined to Entra ID?
Device State: Is this device compliant with security policies?
Device Platform: Is this a Windows device?
Risk Level: Is this login considered risky?
Access Control
Based on these signals, administrators can design a conditional access policy to enforce granular access control, such as:
Enforce specific authentication types (e.g., phishing-resistant credentials)
Allow access only from specific device platforms (e.g., Windows only)
Require Entra hybrid-joined device
Block access when a device is not compliant with security policies
Always On VPN
Entra Conditional Access works with Always On VPN by issuing a special, short-lived user authentication certificate once the user has been authorized. The Always On VPN infrastructure can be configured to use this certificate to grant access to the VPN. Integrating conditional access with Always On VPN can significantly improve the security posture of organizations using this feature.
Are you ready? In just a few short weeks(!) Microsoft will release the February 2025 security updates. This is a critical update because Microsoft plans to enable full enforcement of strong certificate mapping on Active Directory Domain Controllers (DCs) with this release. Administrators unprepared for this may incur outages for workloads using certificate-based authentication such as Always On VPN, Wi-Fi, and others.
Microsoft introduced strong certificate mapping with the May 2022 update KB5014754 to address vulnerabilities identified with certificate-based authentication. The update makes changes to Active Directory Certificate Services (AD CS) certification authorities (CAs) to embed the principal’s Security Identifier (SID) on issued certificates with a new certificate extension. The update also changes domain controller behavior to monitor and optionally enforce strong certificate mapping for authentication.
Enforcement Mode
When first introduced, the update is configured in compatibility mode. If a certificate that isn’t strongly mapped is presented for authentication, an event is recorded in the event log indicating that. Microsoft has been planning for years to enable full enforcement. After many delays, that time is now upon us. Specifically, full enforcement for strong certificate mapping will be enabled by default on DCs after applying the February 2025 security updates.
Note: Administrators can switch back to compatibility mode for now. See below for more details.
Limitations
Initially, the strong certificate mapping update was applied only to online certificate templates. Specifically, those templates are configured to build the subject name from Active Directory information. However, offline templates, where the subject name is supplied in the request, do not include this information by default. Crucially, any certificate issued with Microsoft Intune with PKCS or SCEP uses offline templates and is not strongly mapped. The lack of strong certificate mapping options for Intune-issued certificates forced Microsoft to delay its full enforcement deadline until these limitations were resolved.
Updates
In October 2024, Microsoft Intune announced support for strong certificate mapping for PKCS and SCEP certificates. Administrators can now configure these certificates to include strong certificate mapping. However, administrators must take action to affect this change.
PKCS
To enable strong certificate mapping for PKCS certificates, administrators must ensure that the certificate connector is running at least version 6.2406.0.1001. In addition, the following registry key must be configured on the connector server.
The Intune Certificate Connector server must be restarted for this change to take effect. No changes are required on the PKCS certificate policy in Intune.
SCEP
To enable strong certificate mapping for SCEP certificates, administrators must add the following attribute/value pair to the Subject alternative name settings on their existing Intune SCEP certificate policy.
Attribute: URI Value: {{OnPremisesSecurityIdentifier}}
Preparation
Administrators using certificate-based authentication against on-premises Active Directory should ensure all user and device authentication certificates include embedded SID information. For certificates issued on-premises, with Intune using PKCS or certificates issued by Entra Conditional Access, the certificate should now have the extension 1.3.6.1.4.1.311.25.2, including the principal’s SID.
SCEP certificates issued using Intune will include the following information in the Subject Alternative Name field.
URL=tag:microsoft.com,2022-09-24:sid:<sid>
Note: This applies to certificates issued using Cloud PKI for Microsoft Intune as those certificates are deployed using a SCEP device configuration policy.
Opt-Out
With the February 2025 security update, all domain controllers will be switched to full enforcement mode. Authentication requests using certificates without strong mapping will be denied in this configuration.
If your organization is not prepared to move to full enforcement mode, the February 2025 update allows administrators to opt out and switch back to compatibility mode by enabling the following registry key on all domain controllers.
Administrators are strongly encouraged to update all user and device authentication certificates before September 2025. With the September 2025 security update, Microsoft will no longer honor the opt-out registry settings and strictly enforce strong certificate mapping for all certificate-based authentication requests.
Troubleshooting
Certificate authentication is commonly used for Always On VPN and Wi-Fi authentication. If full enforcement mode is enabled on domain controllers and a certificate is presented for authentication that is not strongly mapped, administrators may see the following event log information recorded on the Network Policy Server (NPS).
Network Policy Server denied access to a user.
The details of the event include the following.
Reason Code: 16 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.
Obviously, the user does not enter their password when using certificates for authentication. However, the indication of a credential mismatch can be caused by missing strong certificate mapping information when the DC is in full enforcement mode.
Note: There are other causes for reason code 16 failures on NPS. Further investigation may be required to determine the root cause.
With the October 2024 Intune update, Microsoft introduced support for strong certificate mapping for certificates issued by Intune via the Intune Certificate Connector. Enabling strong certificate mapping support in Intune is an important change for those organizations using Microsoft Intune to issue and manage certificates for their users and devices, as it resolves a critical implementation blocker.
Note: This post was updated to clarify that adding the {{OnPremisesSecurityIdentifier}} for PKCS certificates is not required. This variable is only used for SCEP certificates.
Background
In May 2022, Microsoft released security update KB5014754, which added functionality to domain controllers and enterprise issuing certification authority (CA) servers, allowing the Kerberos Key Distribution Center (KDC) to enforce strong certificate mapping. Specifically, with KB5014754 installed, issuing CAs now add the requesting principal’s Security Identifier (SID) to the certificate in a new certificate extension. Domain controllers can be configured to reject authentication requests using certificates that do not include this information.
Today, DCs with KB5014754 installed will still allow authentication without strong certificate mapping. However, Microsoft has stated they will begin enforcing strong certificate mapping in February 2025, with an option to disable it via the registry. Starting in September 2025, full enforcement will be mandatory.
The initial changes in KB5014754 applied only to online certificate templates, meaning those that build the subject name from Active Directory. However, deploying certificates with Intune using either PKCS or SCEP requires using an offline certificate template that allows the requestor to supply the subject name in the request. When using offline templates, a certificate is issued but does not embed the SID in the certificate. Using offline templates presents unique challenges to organizations moving to modern management with Intune and Entra ID.
Intune Changes
The October 2024 Intune update addresses this limitation by providing a method to include SID information in certificates using either SCEP or PKCS.
SCEP
To include the SID information in SCEP certificates, create or edit an existing SCEP device configuration policy and define a URI Subject Alternative Name (SAN) attribute with the value {{OnPremisesSecurityIdentifier}} as shown here.
PKCS
To include SID information in PKCS certificates, administrators must ensure the Intune Certificate Connector is updated to at least version 6.2406.0.1001. In addition, a registry setting must be enabled on the Intune Certificate Connector server.
On the server where the Intune Certificate Connector is installed, open the registry editor, navigate to HKLM\Software\Microsoft\MicrosoftIntune\PFXCertificateConnector, and change the value of EnableSidSecurityExtension to 1.
Optionally, administrators can update this setting at the command line by running the following PowerShell command.
Once complete, restart the Intune Certificate Connector server for the changes to take effect.
Certificates
SID information is added to certificates differently depending on which Intune device configuration policy type is used.
PCKS
PKCS certificates have the SID embedded in the certificate extension 1.3.6.1.4.1.311.25.2, as shown here.
SCEP
SCEP certificates have the SID embedded in the Subject Alternative Name (SAN) field in the format “tag:microsoft.com,2022-09-14:sid:<SID>” as shown here.
Migration
When making these changes to embed the SID in Intune-issued certificates in an existing Intune PKCS or SCEP configuration policy, the change will only affect certificates issued after the change is made. To update all certificate holders, you must create and deploy a new device configuration policy to targeted users or devices. Deleting the old profile (or ensuring it no longer applies) will remove the old certificate from the endpoint. If you’ve configured your Intune Certificate Connector to support revocation, the old certificate will also be revoked.
Entra Conditional Access
Entra Conditional Access certificates have included SID information since July 2023. More details here.
Intune Cloud PKI
The changes above will also work with certificates issued by Cloud PKI for Intune.
Other Cloud PKI Providers
Many other Cloud PKI providers, such as SCEPman and KEYTOS, already include the embedded SID in their certificates. Other cloud PKI providers may also include embedded SID. Consult your provider to confirm.
