Watch for users being routed into non-phishing-resistant methods, unusual browser extension activity, unsupported browser prompts, and recovery events that re-authorise new devices. Those signals show that the enterprise is relying on the weakest branch of the sign-in flow rather than the intended passkey control.
How passkey assurance breaks down in the real sign-in flow
Passkey assurance is strongest when the passkey is the normal path to sign in, and it remains the path through enrollment, device binding, and recovery. Breakdown usually starts when the user is allowed to fall back to something weaker, or when the system quietly treats a non-passkey event as equivalent to a passkey-authenticated session.
One useful way to think about this is that the control is not just the cryptographic authenticator, it is the whole assurance chain around it. If the browser, device, identity provider, or help desk can steer the user around the passkey without a hard policy decision, the assurance level drops even though the interface may still look “modern.”
That is why support for phishing-resistant sign-in has to be read together with recovery, browser compatibility, and exception handling. NIST SP 800-63 Digital Identity Guidelines are useful here because they frame authenticator assurance as more than a single login event, they also cover the conditions under which the authenticator remains trustworthy.
What the warning signals usually mean
The clearest warning is a forced or frequent fallback to non-phishing-resistant methods such as password plus OTP, SMS, or push approval. That tells you the passkey is no longer the default control, so the organisation is depending on the least resistant branch of the flow whenever something goes wrong.
Browser extension prompts and unusual extension activity are another strong signal because extensions can change the integrity of the local sign-in experience, including how credentials are entered, intercepted, or redirected. Unsupported browser prompts matter for a different reason: they show that the user is being moved into a less controlled path where the passkey experience may be downgraded, bypassed, or replaced by a fallback method.
Recovery events are especially important because they often create a new trusted device, not just a new login. If recovery can re-authorise a device without strong proofing, then an attacker who reaches the recovery path may gain the same standing as a legitimate passkey holder. The Passwordless and Passkeys Guide and Workforce Identity Security Guide both reinforce that recovery and enrollment are part of the control, not side issues.
Where assurance usually fails first
The first failure point is often policy inconsistency. A system may advertise passkeys, but still permit legacy factors, device prompts, or account recovery paths that effectively outrank the passkey when friction appears. The second failure point is user experience pressure, where support teams or product teams quietly optimise for login success rather than assurance.
The third failure point is re-binding trust after a device change. If a new phone, new browser, or new authenticator can be approved too easily, then the organisation has not really preserved passkey assurance, it has only made the initial sign-in flow stronger. Recovery should be treated as an attack surface, not a convenience feature, because it is where many assurance downgrades become durable.
For broader context on how weaker authentication paths get abused in practice, the MFA Guide is a useful companion, and the Twilio 0ktapus breach 2022 shows why fallback methods and recovery paths remain attractive to attackers even when stronger sign-in options exist.
Risk and Threat Considerations
When passkey assurance breaks down, the main risk is not that passkeys stop working, it is that they stop being the effective gate to access. Once fallback paths, recovery flows, or browser-mediated exceptions become easier to reach than the passkey path, attackers will target those weaker branches because they offer a lower-friction way into the same account.
Failure mechanism: Assurance erodes when policy allows alternate sign-in or recovery routes to grant equivalent trust without matching verification strength, or when local browser and extension behaviour can alter the intended passkey flow.
Impact: The result is account takeover exposure, weaker authentication than the business assumes, and a false sense of phishing resistance that can persist until a recovery event, support interaction, or device change reveals the gap.
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 governance and control requirements practitioners need to meet.
| Framework | Control / Reference | Relevance |
|---|---|---|
| NIST SP 800-63 | Digital Identity Guidelines | Passkey assurance depends on authenticator strength and recovery rules. |
| Recommendation — Align sign-in and recovery flows to phishing-resistant assurance requirements. | ||
| NIST SP 800-53 Rev 5 | IA-2 — Identification and Authentication (Organizational Users) | User sign-in assurance breaks when weaker alternate authenticators are accepted. |
| IA-5 — Authenticator Management | Recovery, replacement, and lifecycle handling determine whether passkey assurance holds. | |
| Recommendation — Enforce strong authentication paths for workforce access. Tighten authenticator issuance, rotation, and revocation controls. | ||
| OWASP ASVS | V6 — Authentication | Passkey assurance breakdown is an authentication-flow problem involving fallback and recovery. |
| V10 — OAuth and OIDC | Federated login and token-based sign-in paths can undermine passkey assurance if misused. | |
| Recommendation — Verify phishing-resistant authentication and restrict weaker fallback options. Check federation flows for assurance downgrades and unsafe re-authentication. | ||
Practitioner Guidance
What to verify: Confirm that passkey enrollment, normal sign-in, step-up, and recovery all have explicit assurance rules. The question is not whether passkeys exist, it is whether any alternate path can create the same session authority with weaker proof.
Decision rule: If a user can regain access through support, browser fallback, or a legacy factor without a materially stronger verification step than normal sign-in, treat that path as an assurance downgrade, not as an acceptable convenience option.
What to measure: Track the rate of fallback authentications, recovery-assisted re-enrolments, unsupported-browser sign-ins, and new-device approvals after recovery. Rising volume in those events is often the earliest indicator that passkey assurance is being bypassed rather than enforced.
Practitioner takeaway: The right question is not “Are we using passkeys?” but “Can any recovery or fallback path confer the same access with less resistance?” If yes, the control is already degrading.
Related resources from NHI Mgmt Group
- What are the signs that security key lifecycle management is breaking down in an organisation?
- What are the signs that user access management is breaking down in a growing organisation?
- What are the signs that security questionnaire handling is breaking down?
- What signs show that CPRA consumer-rights handling is breaking down?
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Reviewed and updated by the NHIMG editorial team on October 8, 2026.
NHI Mgmt Group — the #1 independent authority on Non-Human Identity, IAM, and Agentic AI security. nhimg.org