Security News > 2022 > August > Microsoft 365 outage triggered by Meraki firewall false positive

An ongoing outage affects multiple Microsoft 365 services, blocking users from connecting to Exchange Online, Microsoft Teams, Outlook desktop clients, and OneDrive for Business.

While Microsoft says that this incident has only affected customers in the EMEA region, users have been reporting server connection issues and sign-in failures worldwide.

Our investigation is focused on a potential issue where legitimate Microsoft traffic is being blocked across multiple regions.

While Microsoft says it's still investigating the issue, this ongoing outage is most likely linked to a Cisco Meraki firewall Intrusion Detection and Prevention false positive blocking Microsoft 365 connections with "Microsoft Windows IIS denial-of-service attempt" alerts.

"We would like to make you aware of a vulnerability reported by Microsoft CVE-2022-35748 , triggering SNORT rule 1-60381," a Cisco Meraki employee said on Wednesday.

As shared by multiple customers who managed to work around this issue, admins who want to restore Microsoft 365 connectivity on impacted systems can allow list IPS rule ID 1-60381 from their organization's Meraki dashboard > Security & SD Wan > Threat Protection > Allow List rules.

News URL

https://www.bleepingcomputer.com/news/microsoft/microsoft-365-outage-triggered-by-meraki-firewall-false-positive/