Duplicate accounts, incorrect subject matching, and account takeover through weak linking logic are the main failure modes. Passwordless authentication can verify the login event while still leaving the organisation unsure which managed account the event should update. The control failure is not the passkey itself, but the absence of explicit binding and re-verification around the account record.
Why passkeys alone do not establish the right account record
Adding passkeys to Auth0 changes how a user proves they are authentic, but it does not by itself answer which internal account that authentication event should be attached to. If the tenant already has duplicate profiles, stale identities, or weak recovery paths, the sign-in can succeed while the platform still updates the wrong subject or creates another account instead of binding the event to the intended one.
The practical issue is that authentication and account resolution are separate decisions. A passkey can confirm possession of a phishing-resistant credential, yet the application still needs deterministic rules for subject matching, merge logic, and re-verification before it treats the login as belonging to a specific managed account.
That is why passkey rollouts often fail at the identity-record layer rather than the authenticator layer. The control gap is usually in linking logic, account recovery, and lifecycle governance, not in WebAuthn or FIDO2 itself. Passwordless and Passkeys Guide covers the rollout decisions that matter when you are binding passwordless sign-in to a stable account record.
Where incorrect subject matching comes from
Incorrect subject matching usually appears when an organisation allows more than one identifier path to point at the same human, such as email changes, legacy usernames, social logins, or a migrated directory record. If the account-linking step is loose, the platform may treat a fresh passkey login as evidence for the wrong profile, or may let a new profile inherit the wrong entitlements.
That failure becomes more likely when account creation, login, and recovery are not tightly separated. A sign-in can be successful from an authentication standpoint while the application still cannot prove that the credential belongs to the record being updated. In practice, this is the point where duplicate accounts, orphaned accounts, and silent merges begin.
Strong account binding needs re-verification of the existing account, not just a completed authentication ceremony. NIST SP 800-63 Digital Identity Guidelines is useful here because it separates authentication strength from identity proofing and account lifecycle decisions. Workforce Identity Security Guide is a good companion for the broader account binding and recovery pattern.
Why weak linking logic can become account takeover
Weak linking logic turns a convenience feature into an attack surface when an adversary can control the account-matching inputs, recover an account through a lower-assurance path, or persuade support staff to connect a passkey to the wrong profile. The attacker does not need to defeat the passkey itself if they can exploit the workflow that decides which account the passkey is allowed to update.
That means the highest-risk cases are not just duplicate accounts, but bad recovery and bad exception handling. A privileged or high-value account that can be relinked without strong re-verification can be taken over even when the passkey authentication step is functioning exactly as designed.
Break-Glass and Emergency Access Account Guide is relevant because exceptional access paths often become the place where account-linking discipline breaks down. MFA Guide reinforces the broader point that strong sign-in does not remove the need for careful recovery and step-up controls. For authoritative control mapping, NIST SP 800-53 Rev 5 Security and Privacy Controls provides the access-control and identity-control structure that should govern those binding decisions.
Risk and Threat Considerations
The main risk is that passkey adoption creates a false sense of closure: authentication looks stronger, but account binding remains ambiguous. That gap can produce duplicate identities, privilege drift, and unauthorized updates to the wrong user record, especially during migration, recovery, or help desk intervention.
Failure mechanism: The attacker or mistake path exploits the separation between successful authentication and correct subject resolution, then uses weak merge, recovery, or support workflows to bind the credential to the wrong account.
Impact: The organisation may end up with silent account takeover, cross-account entitlement contamination, or a managed account that is authenticated but not correctly owned.
Standards & Framework Alignment
This section maps relevant standards and security frameworks to the operational risks and controls described in this guidance.
NIST SP 800-63, NIST SP 800-53 Rev 5 and OWASP ASVS set the technical controls, while ISO/IEC 27001:2022 defines the regulatory obligations.
| Framework | Control / Reference | Relevance |
|---|---|---|
| NIST SP 800-63 | Digital Identity Guidelines | Separates authentication strength from identity proofing and account binding. |
| Recommendation — Use identity proofing and re-verification before linking a passkey to an existing account. | ||
| NIST SP 800-53 Rev 5 | IA-5 — Authenticator Management | Passkey enrollment and lifecycle require controlled authenticator binding and rotation. |
| IA-2 — Identification and Authentication (Organizational Users) | The subject concerns user authentication to managed accounts and correct subject association. | |
| AC-2 — Account Management | Duplicate accounts and linking logic are account-management failures, not just login issues. | |
| Recommendation — Govern passkey enrollment, reassignment, and revocation under authenticated lifecycle controls. Require strong user authentication before account updates or linking actions are accepted. Maintain authoritative account records and block silent merges or duplicate profile creation. | ||
| ISO/IEC 27001:2022 | A.5.16 — Identity management | Binding passkeys to the right subject depends on controlled identity lifecycle management. |
| Recommendation — Define ownership and lifecycle rules for account linking, recovery, and deprovisioning. | ||
| OWASP ASVS | V6 — Authentication | Passkey login security must be paired with correct authentication and recovery handling. |
| Recommendation — Verify enrollment and step-up flows preserve the intended user-to-account binding. | ||
Practitioner Guidance
What to verify: Treat account linking as a controlled security function, not a convenience feature. Verify that every passkey enrollment, merge, and recovery path requires the same identity checks that would be expected for a privileged account change, and that the system cannot silently link on email alone or on a weak historical identifier.
Decision rule: If the user already has an existing record, require explicit re-verification before linking the new passkey, and block automatic merges unless the account owner and the authoritative directory record are both confirmed.
Common mistake: Teams often assume that phishing-resistant sign-in means the account is now safely bound. In reality, the binding decision is only trustworthy when the application, directory, and recovery workflow all resolve to the same subject.
Practitioner takeaway: A passkey can harden authentication, but it cannot compensate for ambiguous account identity. If the binding logic is weak, the control problem simply moves from password theft to subject confusion.
Related resources from NHI Mgmt Group
- What breaks when passkeys are synced without strong account recovery controls?
- What breaks when account takeover controls focus only on login security?
- What breaks when shared accounts move to passkeys without lifecycle controls?
- What breaks when AI agents are added to an IAM programme without new controls?