In September 2025, cybersecurity researchers uncovered a sophisticated command-and-control (C2) framework named MeetC2, which exploits Google Calendar APIs to establish covert communication channels between attackers and compromised systems. This development signifies a concerning evolution in cyberattack methodologies, where threat actors leverage trusted cloud services to bypass traditional security controls and evade detection mechanisms.
Understanding MeetC2’s Operation
MeetC2 operates by disguising malicious traffic as routine business communications through Google’s widely trusted domains, specifically oauth2.googleapis.com and www.googleapis.com. This tactic allows malicious activities to blend seamlessly with normal organizational traffic, making detection significantly more challenging for security teams. The framework’s cross-platform compatibility across macOS and Linux systems further amplifies its potential impact on diverse enterprise environments.
Technical Implementation and Evasion Mechanisms
The technical architecture of MeetC2 reveals sophisticated evasion capabilities that exploit the ubiquity and trusted nature of Google services. The authentication process utilizes standard OAuth2 flows, requiring attackers to create legitimate Google Cloud Console projects and service accounts with calendar access permissions. This approach ensures all communications appear as authorized API interactions rather than suspicious network traffic.
The implementation requires minimal infrastructure, operating entirely through Google’s existing Calendar API infrastructure. Operators authenticate through service accounts configured with Make changes to events permissions on shared calendars. The polling mechanism employs a 30-second interval, balancing operational responsiveness and avoiding excessive API requests that might trigger rate limiting or suspicious activity alerts.
Code execution occurs through command extraction from calendar event summaries, with results uploaded back to the same event’s description field. This bidirectional communication model creates a complete command-and-control channel while maintaining the appearance of legitimate calendar synchronization activities. The framework supports targeted command execution using host-specific syntax like exec @host:command or broadcast commands across multiple compromised systems simultaneously.
Broader Implications and Historical Context
The discovery of MeetC2 is not an isolated incident but part of a broader trend where cybercriminals exploit legitimate services to conduct malicious activities. For instance, in late October 2024, the Chinese state-sponsored cyber espionage group APT41, also known as HOODOO, abused Google Calendar as a command-and-control tool. They used specialized malware that stored encrypted commands and exfiltrated data as calendar events, blending malicious activities with legitimate Google Calendar usage. ([cybernews.com](https://cybernews.com/security/chinese-hackers-abuse-google-calendar-for-malware-control/?utm_source=openai))
Similarly, in December 2024, an ongoing phishing scam was reported that abused Google Calendar invites and Google Drawings pages to steal credentials while bypassing spam filters. Attackers sent meeting invites containing links that led to Google Forms or Google Drawings, prompting users to click another link disguised as a reCAPTCHA or support button, ultimately leading to credential theft. ([bleepingcomputer.com](https://www.bleepingcomputer.com/news/security/ongoing-phishing-attack-abuses-google-calendar-to-bypass-spam-filters/?utm_source=openai))
Mitigation and Prevention Strategies
To defend against such sophisticated attacks, organizations and individuals should consider the following strategies:
1. Adjust Calendar Settings: Disable the automatic addition of events in Google Calendar. Navigate to Settings, under Event Settings, set Automatically add invitations to No, only show invitations to which I have responded. Uncheck Show declined events to avoid viewing unwanted invitations. ([cybersecsentinel.com](https://cybersecsentinel.com/google-calendar-vulnerability-exposes-users-to-phishing/?utm_source=openai))
2. User Education and Awareness: Inform users about the risk of unsolicited calendar invites. Encourage them to verify the sender before interacting with calendar events.
3. Security Software and Monitoring: Keep antivirus and anti-malware solutions updated. Regularly scan for malicious .ics files and suspicious calendar activity. Monitor logs and email activity for unusual patterns or unexpected calendar entries.
4. Two-Factor Authentication (2FA): Enable 2FA on Google accounts to add an extra layer of protection against credential theft. Even if credentials are stolen, 2FA can help prevent unauthorized account access.
5. Stay Updated: Ensure all software and browsers are up to date with the latest security patches. Apply any security enhancements offered by Google to reduce the likelihood of calendar abuse.
Conclusion
The emergence of the MeetC2 framework underscores the evolving tactics of cybercriminals who exploit trusted cloud services to conduct malicious activities. By leveraging Google Calendar APIs, attackers can establish covert communication channels that are difficult to detect. Organizations and individuals must remain vigilant, adopt robust security measures, and stay informed about emerging threats to protect against such sophisticated attacks.
