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HOLLOWGRAPH Backdoor Turns Microsoft 365 Calendars Into a C2 Channel

📅 July 29, 2026 📰 www.picussecurity.com 🔍 0 CVE(s) referenced

HOLLOWGRAPH is a stealthy Windows backdoor that hijacks Microsoft 365 calendar events as an encrypted command-and-control channel, using hybrid cryptography and DNS tunneling to evade detection and maintain persistent access for espionage and data exfiltration.

unclassified

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