Google has issued a warning about a threat involving a public proof-of-concept exploit named
Google Calendar RAT (GCR, remote access trojan). This tool utilizes Google Calendar Events for remote command-and-control (C2) purposes through a Gmail account. The exploit was published on GitHub in June 2023, creating a hidden channel by manipulating event descriptions in Google Calendar.
This has not been observed in active use, Mandiant threat intelligence unit has identified multiple threat actors sharing the proof-of-concept on various forums.
Methods
The Google Calendar RAT (GCR) operates on compromised machines. It is regularly checking the Calendar event description for new commands. It executes these commands on the targeted device and updates the event description with the command output. The tool's use of legitimate infrastructure poses a challenge for defenders as it makes detecting suspicious activity more difficult.
Recommendation
1. Users and organizations are advised to stay vigilant, update security measures, and be cautious of potential threats exploiting cloud services, as demonstrated by the GCR tool.
2. Security teams should be aware of the evolving tactics used by threat actors to abuse legitimate platforms for malicious activities.
3. Beware of any suspicious activities' in your google account for various services.
Conclusion and Security Impact
Attackers are using various, advanced and innovative techniques to abusing cloud services to operate within victim environments while avoiding detection. Notably, the GCR tool's use of Google Calendar for C2 activities makes it challenging for defenders to detect and respond to the threat.
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