Block New PassKey Registrations: Real Security Gap or IT Policy Overreaction?

When an organization blocks new PassKey registrations, it is preventing future credentials from being added. It is not revoking the ones already registered.

That distinction sounds minor. In practice it is the reason some IT teams wake up to an incident they did not expect.

Why organizations block new PassKey registrations

The logic is straightforward. PassKeys are phishing-resistant and do not rely on shared secrets the way passwords do. When a user registers a PassKey, that credential is scoped to a specific device and a specific domain. A PassKey registered to google.com will not authenticate against paypal.com.

Organizations that want to limit authentication to managed, known devices use the blocking policy to prevent users from adding personal devices or unregistered security keys to their corporate accounts. It is a hardening measure that treats new credential additions as a risk event rather than normal user behavior.

What the policy actually does

Blocking new PassKey registrations stops a user from adding a new credential to their account through the normal registration flow. It does not affect any PassKey already registered.

This means the following scenario is not prevented by the blocking policy:

• Employee registers a PassKey on their personal laptop during a work-from-home period
• IT team enables the blocking policy
• The personal laptop remains registered and the PassKey on it stays active
• If the laptop is lost, stolen, or the employee leaves under bad terms, that credential is still functional

The credential lifecycle problem is what the blocking policy ignores. It was designed to prevent new risk, not to address risk that already exists in the form of registered credentials on devices the organization does not control.

When blocking creates a false sense of security

The policy becomes a liability when IT teams treat it as equivalent to credential control. The actual risk surface looks like this.

Orphaned credentials are registered PassKeys on devices no longer under corporate control. A personal laptop that a user formatted and sold with a work PassKey still registered. A former contractor's phone that was not deprovisioned. These credentials remain active unless someone explicitly revokes them.

The blocking policy does not touch any of this. It just stops new ones from being added to the pile.

Phishing resistance regression is another overlooked consequence. Organizations that block PassKey registrations without providing an approved alternative sometimes push users toward password-based authentication. Passwords are more susceptible to phishing. The hardening policy can end up weakening the overall authentication posture if the user journey is not designed carefully.

Entitlement drift happens when an employee moves to a new role or leaves the company. Their registered PassKeys typically remain active unless the offboarding process explicitly includes credential revocation. Blocking new registrations does nothing to close this gap.

How to handle orphaned credentials properly

Revocation is the control. Registration blocking is just the guard at the door.

For lost or stolen devices, the registered PassKey must be revoked in the admin console. In Microsoft 365, this is available through the Azure Active Directory portal or the My Sign-ins security info page. In Google Workspace, the Admin console provides a security key management interface.

For MDM-enrolled devices, remote wipe removes the credential along with everything else on the device. For personal devices that are not MDM-managed, explicit revocation in the admin console is the only way to deactivate the credential.

For offboarding, credential revocation must be part of the standard offboarding checklist, not an afterthought. Revoke the account access, revoke the session tokens, and revoke the registered PassKeys. These are three separate actions.

For inventory, most organizations do not have a continuous picture of what PassKeys are registered across their user base. This is the most practical gap to address. A quarterly review of registered credentials per user account, cross-referenced against the active employee roster, surfaces orphaned entries that can then be revoked.

When the blocking policy makes sense

The blocking policy is appropriate in specific environments.

Organizations that have completed a passwordless transition in Microsoft Entra ID and want to enforce that all authentication happens through managed credentials only. In this case, the blocking policy reinforces an existing control rather than compensating for a gap.

High-security environments where hardware security keys are the only permitted authenticator. Blocking registration enforces the constraint rather than relying on user compliance.

Controlled rollout scenarios where PassKey adoption is being managed in phases. The policy prevents users from registering devices outside the approved deployment.

The blocking policy makes less sense when there is no inventory of what is currently registered, when offboarding does not include credential revocation, or when the main goal is reducing IT tickets rather than reducing authentication risk.

Email authentication as a complementary security layer

PassKeys protect authentication at the identity provider level. They do not protect against phishing emails that impersonate a brand or that try to direct users to look-alike login pages.

Email authentication protocols like DMARC address a different attack surface. DMARC reports surface attempts to send email from domains you control but from servers you did not authorize. These reports reveal who is trying to impersonate your domain and whether their messages are reaching recipients.

This matters for organizations running PassKeys because phishing campaigns targeting your users will not be stopped by your PassKey policy. A phishing email that spoofs your brand and points to a fake login page will reach inboxes regardless of whether your users have registered PassKeys. DMARC monitoring detects these campaigns and tells you whether they are succeeding.

Organizations that have deployed PassKeys often have stronger authentication but the same email domain protection gaps they had before. Adding DMARC monitoring to the security stack closes that gap in a way that PassKey deployment alone does not. DMARC reports are lightweight, require no user action, and do not interfere with PassKey or any other authentication mechanism.

Bottom line

Blocking new PassKey registrations is not a security gap. It is a hardening policy with a credential lifecycle visibility gap built into its design.

The organizations that get this right combine the blocking policy with three practices: an active inventory of registered credentials, a revocation process that fires on device loss and employee offboarding, and a user journey that does not push users back toward passwords.

The organizations that run into trouble treat the blocking policy as the control. It is not. It is a prevention mechanism that works only when paired with the actual control: revocation with inventory.

FAQ

Does blocking PassKey registrations create a security gap?

It creates a credential lifecycle visibility gap. Blocking new registrations stops new credentials from being added. It does not deactivate credentials that are already registered on devices you do not control. If a lost or stolen device has an active PassKey, that credential can still be used regardless of the blocking policy.

What is the difference between registration and authentication for PassKeys?

Registration is the act of adding a new PassKey to an account. Authentication is the act of using an already-registered PassKey to sign in. Blocking registration prevents new credentials from being added. It has no effect on credentials already registered.

Can a PassKey be used by someone who is not the registered user?

Only with physical access to the registered device. PassKeys are bound to the device and require the device unlock factor to activate. If the device is secured with a strong unlock factor, the PassKey on it is not accessible to someone who does not own or control that device.

Can IT administrators revoke a registered PassKey?

Yes. Both Microsoft 365 and Google Workspace provide admin interfaces for revoking registered security keys. The credential is invalidated immediately upon revocation and can no longer be used for authentication.

What happens when a device with a registered PassKey is lost or stolen?

The PassKey on that device remains active until explicitly revoked. If the device is MDM-managed, remote wipe removes the credential. For personal devices, explicit revocation in the admin console is the only way to deactivate the credential.