Why do passkeys not solve session takeover and fraud by themselves?

Why passkeys improve login security but not post-login abuse

Passkeys change how a user proves they are legitimate at sign-in. They are strong against phishing, password reuse, and many credential-theft paths, but they do not by themselves stop an attacker who is already inside an active session, has stolen a session token, or can abuse a trusted device after login.

That is why passkeys should be treated as a sign-in control, not a complete fraud-control strategy. The security boundary moves from secret capture at authentication to what happens after authentication, where session handling, device trust, and step-up policy become decisive.

What remains exposed after the passkey ceremony

Once authentication succeeds, the application usually relies on cookies, tokens, device state, or remembered trust to keep the user signed in. If an attacker steals that runtime state, hijacks a browser session, or compromises the endpoint, the fact that the original login used a passkey does not invalidate the already-issued session.

That is the core limitation: passkeys protect the authentication event, not every subsequent action. Fraud often happens after the login gate, through account changes, payment abuse, data export, contact-detail edits, beneficiary changes, or privilege escalation within the authenticated workflow.

For teams hardening sign-in flows, the practical lesson is to pair passkeys with controls that understand session age, device posture, location shifts, unusual transaction patterns, and reauthentication triggers. Guidance on Passwordless and Passkeys and Workforce Identity Security both reinforce that phishing-resistant login is only one layer of the overall trust model.

Why fraud controls still need context, step-up, and session-aware policy

Fraud prevention depends on runtime decisions, not just a stronger authenticator. A passkey can confirm possession of a registered credential and device at the moment of login, but it cannot on its own determine whether the current action is normal, whether the session should still be trusted, or whether the user’s behaviour now differs from their baseline.

That is why mature programs combine passkeys with step-up authentication for high-risk actions, short-lived sessions for sensitive workflows, token binding or sender-constrained designs where appropriate, and policy engines that can interrupt suspicious activity mid-session. Session and token controls are especially important when the abuse path involves replay, cookie theft, or a compromised browser context.

Passkeys also do not remove the need to secure recovery, help-desk reset, federation, or identity-provider administration. If an attacker can reset the account, take over the device, abuse recovery, or steal an active session from the IdP side, they may bypass the passkey protection entirely. For that reason, Identity Provider and SSO Security remains highly relevant even in passkey-first environments.

Risk and Threat Considerations

Fraud and takeover risk shifts, it does not disappear. Once attackers stop targeting passwords and start targeting sessions, devices, recovery paths, and trusted workflows, the main exposure becomes post-authentication abuse that looks legitimate to the application.

Failure mechanism: An attacker reuses a valid session, steals a session token or cookie, compromises the endpoint, or exploits a recovery path and then performs sensitive actions inside an already-authenticated context.

Impact: The organisation can still see account takeover, payment fraud, data exfiltration, or privilege abuse even when passkeys are deployed correctly, because the compromise happens after the sign-in control has already succeeded.

Practitioner Guidance

What to prioritise: Treat passkeys as the front door, then decide which post-login actions deserve additional checks. High-risk actions such as payout changes, new device enrollment, recovery changes, and API/token issuance should not inherit the same trust as a routine page view.

What to verify: Confirm that your session controls actually expire, revalidate, or step up when risk changes. If a stolen cookie or browser session can survive long enough to complete a fraud path, the passkey rollout is incomplete from a defence standpoint.

What good looks like: A strong deployment uses passkeys for phishing-resistant sign-in, then layers continuous session evaluation, device-bound trust where feasible, and targeted reauthentication for sensitive operations. The objective is bounded runtime trust, not just stronger login.

Practitioner takeaway: Passkeys reduce credential theft, but they do not remove the need to govern the session that follows; most real abuse now hinges on whether you can still trust the authenticated context after login.

Related resources from NHI Mgmt Group

• Why do passkeys and phishing-resistant MFA not solve fraud on their own?
• How should security teams use passkeys to reduce account takeover fraud?
• Why do passkeys alone not fully solve account takeover risk in high-assurance journeys?
• What are the signs that a mobile app is exposed to on-device fraud and session takeover?