H-ISAC TLP White Informational: Microsoft Defender Portal Outage

On December 2, 2025, Microsoft experienced a widespread outage in its Defender Portal that prevented many organizations from accessing critical security alerts and threat-hunting data. According to reports, the outage lasted for over 10 hours.

Microsoft initially acknowledged the issue at 06:10 UTC. Microsoft customers can view more information about the outage via their Admin Center Service Alert, under the Alert ID: DZ1191468

Mitigation measures have been implemented by Microsoft to address the impact and increase processing throughput, with telemetry indicating that availability has recovered for some affected customers, according to an 08:00 UTC update.

Health-ISAC is sharing this to increase situational awareness.

View the detailed report below.