Microsoft 365 outage takes down Office web apps, admin center

Microsoft is investigating a widespread and ongoing Microsoft 365 outage impacting Office web apps and the Microsoft 365 admin center.

Since this incident started hours ago, Downdetector has received user reports complaining about problems connecting to Outlook, OneDrive, and other Office 365 apps and services.

Affected customers see "We're experiencing a service outage. All of your open files have been saved. It may be some time before the outage is resolved." messages when trying to view or access their Microsoft 365 apps using a web browser.

"We're focussing our investigation on token generation within our authentication infrastructure. In parallel, we're reviewing recent changes to determine the root cause," Microsoft said in an incident alert published in the admin center.

"Impact is specific to some users, who are served through the affected infrastructure, attempting to access apps in Microsoft 365 for the web."

Microsoft advises affected users to access their Microsoft 365 apps and documents using the desktop applications (if they have the required licenses) as a workaround.

At the moment, Microsoft's service status, service health status, and Microsoft 365 network health status pages currently show no issues affecting the Microsoft 365 admin center, the company's network health status, internet service provider availability, and customer network infrastructure.

A worldwide Microsoft 365 outage also impacted multiple services and features two weeks ago, including Microsoft Teams, Exchange Online, SharePoint Online, OneDrive, Purview, Copilot, and Outlook Web and Desktop.

The incident was resolved after more than 24 hours, with the company saying it was still "addressing lingering issues with Outlook on the web" and "investigating mail queuing delays causing longer delivery times."

In July, another massive outage took down multiple Azure and Microsoft 365 services, like the admin center, Intune, Entra, Power BI, and Power Platform services.

One day later, Redmond admitted that the nine-hour outage was triggered by a distributed denial-of-service (DDoS) attack amplified by an error in its DDoS protection mechanisms.

Update December 10, 07:55 EST: Microsoft is currently testing a potential fix that is expected to resolve these ongoing issues.

"While we continue to investigate the root cause, we've identified a token generation issue which may be contributing towards the impact. We're testing a fix to revert to an alternate token generation flow, which we believe will resolve the issue," the company said.