Credit: Microsoft

A number of Microsoft Azure and Office 365 users have been unable to get into their accounts for most of the day on November 19. The problem: A multi-factor authentication issue which hit users worldwide and left them unable to sign into their services.

The Office 365 status page noted that affected users may be unable to sign in using multi-factor authentication (two-factor authentication) and may also be unable to do self-service password resets.

"A subset of users are no longer receiving prompts on their mobile devices (SMS, call or push) and (we) are investigating diagnostic logs to understand why," the status dashboard noted.

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Azure and Office 365 MFA services were affected starting at 4:39 am UTC (which was 11:39 pm ET the previous day), according to the Office status page.

The Azure status page noted that those affected may have had problems signing into Azure resources like Azure Active Directory, when MFA was required.

Azure engineers reported around noon ET today that they had deployed a hotfix , but that it took time to take effect across impacted reasons, and in particular Europe and Asia-Pacific. Engineers were reporting they have seen a reduction in authentication errors as a result of the hotfix. The hotfix also tipped off engineers that some subset of customers were not receiving SMS, Call or Push prompts for MFA.

"Engineers are continuing to explore additional workstreams and potential impact to customers in other Azure regions to fully mitigate this issue," the Azure status page noted.

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Beyond those status reports, Microsoft hasn't shared information as to what caused the MFA services problem today.

Update (4:30 pm ET): I'm hearing from more users that the MFA issue seems to be mostly over. The Azure status page now says all services are running normally. The Office 365 status page says:

"We've observed continued success with recent MFA requests and are taking additional actions in the environment in an effort to prevent new instances of this problem. Our investigation into the root cause of this problem is ongoing and maintained as our highest priority.



Update (November 21): According to a preliminary root cause analysis provided by MIcrosoft on its Microsoft 365 Admin Health Center:

"A recent update to improve conections to caching services for the MFA service introduced an issue that prevented users from being able to sign in or carry out self-service password resets when using MFA for authentication."

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