Yubikey FIDO keys stopped working. Outlook requiring a code from Authenticator App

Brian Krehbiel 5 Reputation points
2024-10-22T19:53:45.4266667+00:00

Suddenly today, a number of users received a notice that their M365 password needed to change when logging in to Outlook. These users normally use a Yubikey FIDO2 key for authentication, but after they changed their password, their MFA was not accepted from the Yubikey. It was requiring the code from an authenticator app that the user has never used. Even after temporarily removing MFA from the users account, their security settins are requiring an MFA app authentication to check their security settings. Even requiring the end user to reset their MFA options doesn't allow them to choose FIDO as an option. This was working until today. The Entra / Azure settings have FIDO as an option for all users, but there is no option for choosing the FIDO key.

Microsoft Security | Microsoft Entra | Microsoft Entra ID
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  1. Navya 20,575 Reputation points Microsoft External Staff Moderator
    2024-11-01T11:07:55.77+00:00

    Hi @Brian Krehbiel

    Thank you for posting this in Microsoft Q&A.

    I understand that some of your users are experiencing a sudden and unexpected change in the authentication process for Microsoft 365 (M365), specifically those who typically use a YubiKey FIDO2 key for multi-factor authentication (MFA).

    To use a YubiKey FIDO2 key, at least one multi-factor authentication method needs to be registered. Could you please try adding a multi-factor authentication method and see if the FIDO key option appears in the security info page?
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    Hope this helps. Do let us know if you any further queries.

    Thanks,

    Navya.

    If this answers your query, do click Accept Answer and Yes for was this answer helpful. And, if you have any further query do let us know.

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