Modern adversaries are moving beyond traditional infrastructure for command-and-control (C2) operations, increasingly hiding malicious traffic inside trusted cloud platforms.
A new proof-of-concept (PoC) tool, MeetC2, underscores how easily popular SaaS services like Google Calendar can be abused to create stealthy, encrypted backchannels that blend seamlessly with legitimate workplace traffic.
MeetC2, developed by Deriv Security, is a lightweight, cross‑platform framework that leverages Google’s Calendar API to demonstrate cloud-based covert communications.
While not designed for malicious use, the tool provides red and blue teams with a reproducible testbed for detection and defense exercises against cloud abuse tactics.
Turning Calendar Events into Covert Channels
Unlike conventional C2 frameworks that rely on attacker-controlled domains or IPs, MeetC2 hides in plain sight by routing traffic through Google’s legitimate APIs (oauth2.googleapis.com and www.googleapis.com).
Once authenticated, a compromised endpoint polls Google Calendar every 30 seconds for newly created events, parsing the organizer’s commands embedded in the event summary field.
For attackers (or red team operators), issuing commands requires nothing more than creating a new calendar event via the API.
A simple POST request to the Calendar endpoint introduces instructions exec whoami disguised as meeting details. Compromised hosts, running MeetC2’s “guest” binary, detect these events during their routine polling and execute the specified instruction.
The response loop is equally subtle: output from the infected host is written back into the same calendar event via a PUT request, encapsulated within designated [OUTPUT] [/OUTPUT] markers in the event’s description.
This bidirectional flow transforms Google Calendar into a serverless and trusted C2 infrastructure, essentially handing adversaries persistence within enterprise workflows where calendar integrations already thrive.
Hands-On Setup & Security Implications
To demonstrate this, MeetC2 requires only a standard GCP setup: enabling Google Calendar API, creating a service account with JSON key credentials, and securely sharing a test calendar with edit permissions.
Once configured, operators can interact with compromised endpoints through a simple CLI organizer tool that supports commands like exec, list, and clear.
For security teams, MeetC2 highlights the difficulty of differentiating benign API calls from malicious C2 traffic when adversaries use sanctioned SaaS domains. Blue-team defenders cannot simply block googleapis.com, as this would disrupt legitimate enterprise workloads.
Instead, organizations must enhance visibility into third-party OAuth permissions, API access patterns, and anomaly detection in cloud logs.
Acknowledging its inspiration from the earlier GC2-sheet project, Deriv Security recommends using MeetC2 exclusively in sandboxed environments.
The project highlights a broader challenge: as businesses adopt SaaS and serverless platforms, defenders must adjust their monitoring to identify when corporate calendar invites can also serve as attacker command channels.
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