HOLLOWGRAPH: Turning Microsoft 365 Calendars into Covert Command-and-Control Channels

Reported 20 Jul 2026 by otx · Severity: medium

A sophisticated espionage campaign has been identified leveraging malware that exploits Microsoft Graph API to transform compromised Microsoft 365 calendars into covert command-and-control infrastructure. The malware creates calendar events dated to 2050 with encrypted attachment