Google has recently issued a warning about a new threat known as GCR (Google Calendar RAT). This threat utilizes the Google Calendar service for covert command and control operations, allowing cybercriminals to transmit data without detection. While it has not been used in actual cyberattacks [4], the public proof of concept (PoC) has raised concerns among security experts [4]. This trend highlights the growing exploitation of cloud services by threat actors for stealthy operations.


GCR operates by creating a hidden channel through event descriptions in Google Calendar. This enables cybercriminals to transmit data without being detected. The use of legitimate infrastructure makes it challenging to identify suspicious activity, making this approach particularly concerning. Google has taken proactive measures to address this threat, including implementing a fix to block the tool and disabling attacker-controlled Gmail accounts associated with the malware. This demonstrates the ongoing trend of threat actors abusing cloud services [1] [2] [3], such as Gmail and Google Calendar, to blend in with victim environments [1] [2] [3].

It is worth noting that a previous instance involved an Iranian nation-state actor exploiting Gmail as their command and control infrastructure. This further emphasizes the need for proactive measures to counter these threats. Google has also identified other instances of threat actors exploiting cloud services [4], such as using macro-laced documents to compromise users with a .NET backdoor [4]. The exclusive use of legitimate infrastructure by these threats makes it difficult for defenders to detect suspicious activity. This highlights the continued interest of threat actors in abusing cloud services to blend in with victim environments and avoid detection [1] [2].


The GCR threat and its exploitation of Google Calendar for covert operations have significant implications. The ability to transmit data without detection poses a serious risk to users’ privacy and security. Google’s proactive actions in addressing this threat demonstrate the ongoing need for vigilance and measures to counter such attacks. As threat actors continue to exploit cloud services, it is crucial for organizations and individuals to remain aware and take necessary precautions to protect themselves.