Device Trust - Attack protection | Clerk Docs

Device Trust

Device Trust is Clerk's defense against credential stuffing⁠ attacks - a type of attack where bad actors use lists of stolen passwords to attempt to gain unauthorized access to user accounts.

When Device Trust is enabled, Clerk treats every new device as untrusted until the user has verified their identity with a second factor⁠.

How Device Trust works

Device Trust automatically requires a second factor⁠ when all of the following conditions are met:

  1. The user enters a valid password.
  2. The user hasn't enabled multi-factor authentication (MFA).
  3. The user is signing in from a new device.

When these conditions are met, Clerk uses an email code, SMS code, or email link based on your settings. The user must complete this verification to finish the sign-in process.

Note

If the user has already enabled MFA (such as an authenticator app or SMS verification), Device Trust will not trigger - their existing MFA method will be used instead.

How long a device remains trusted

Device Trust doesn't have a separate, configurable trust duration. On web applications, Clerk recognizes a browser through the client authentication cookie, so the browser remains trusted for as long as that cookie remains present and valid.

If the cookie expires, is deleted, or is unavailable - for example, after the user clears their browser data, switches browser profiles, or starts a private browsing session without the existing cookie - Clerk treats the browser as a new device and may require second-factor verification again.

You can't configure the Device Trust duration in the Clerk Dashboard or for an individual sign-in attempt. To access the expiration time of the current client's authentication cookie, use the Client.cookieExpiresAt property:

const expiresAt = clerk.client.cookieExpiresAt

For development instances, this property is always null. For production instances, it reports the cookie's current expiration time, but can also be null. Clerk can refresh the client cookie, so this value can change. A user can also delete the cookie before it expires. If you display the value, describe it as the current cookie expiration time rather than a guaranteed Device Trust expiration date.

Note

Device Trust is automatic and Clerk doesn't provide a supported per-sign-in option for changing how long a browser remains trusted. If you build a custom sign-in UI, use informational text to explain how long the browser can remain recognized instead of presenting a "Remember this device" checkbox as a Device Trust setting.

Enable Device Trust

Device Trust is automatically enabled for Clerk applications created after November 14, 2025. For applications created before this date, you can enable Device Trust in the Clerk Dashboard:

  1. In the Clerk Dashboard, navigate to the Rules⁠ page under Protect.
  2. In the Device Trust row, check the Status.

Note

Device Trust requires password-based sign-in to be enabled.

How Device Trust differs from traditional MFA

Aspect Device Trust Traditional MFA
Trigger Automatic on new devices User must enable it
Verification method Email code, SMS code, or email link TOTP, SMS code, backup codes
User setup required None User must configure their preferred method
When it applies Only for password sign-ins All sign-ins

Impact on custom sign-in flows

If you've built a custom sign-in flow⁠ that allows password-based sign-ins using the Clerk API or SDKs, you'll need to handle the needs_client_trust status that Device Trust can trigger.

Note

Device Trust was previously called "Client Trust." The feature was renamed, but its API values - including the needs_client_trust status - kept their original names so that existing integrations keep working.

If an older application has Device Trust enabled but your custom sign-in flow receives the legacy needs_second_factor status instead of needs_client_trust, opt in to the Device Trust Status update on the Updates⁠ page. This update doesn't enable Device Trust. It only changes the custom-flow response from needs_second_factor to needs_client_trust.

When Device Trust requires verification, the sign-in attempt will return a status of needs_client_trust with email_code, phone_code, or email_link in the supportedSecondFactors array. Your flow should:

  1. Check if the sign-in status is needs_client_trust.
  2. Check if email_code, phone_code, or email_link is in the supportedSecondFactors array.
  3. Call prepareSecondFactor() for the selected strategy.
  4. Complete the selected strategy's verification.
  5. If successful, set the session as active.

For a complete implementation example, see the email/password custom flow guide.

Tip

If your application supports both Device Trust and user-enabled MFA, make sure to handle both the needs_client_trust and needs_second_factor statuses. The needs_client_trust status is returned when Device Trust triggers on a new device, while needs_second_factor is returned when the user has MFA enabled on their account.

Limitations