New HollowGraph malware uses Microsoft Graph for stealthy C2 comms

A malicious component called HollowGraph uses the calendar feature in compromised Microsoft 365 mailboxes as a command-and-control channel to receive attacker commands and exfiltrate stolen data. The malware leverages Microsoft Graph for stealthy communications, posing a significant security threat to organizations using Microsoft 365. Security teams are advised to monitor for unusual calendar activity.