Potential Data Exfiltration via Rclone

This detection identifies the potential abuse of rclone, a legitimate command-line program used for managing files on cloud storage, for malicious data exfiltration. Attackers might rename rclone to masquerade it as a security or backup utility and blend it with administrative traffic. They can then use rclone's copy or sync functions with specific cloud backends (like S3) and filters to target and exfiltrate sensitive file types. The use of rclone with suspicious arguments and without legitimate configuration paths can be a strong indicator of malicious activity. This activity is observed on Windows systems. Defenders need to be aware of this technique as it allows attackers to exfiltrate data without using conventional malware.

Attack Chain

1. An attacker gains initial access to a Windows system (e.g., through compromised credentials or exploiting a vulnerability).
2. The attacker downloads rclone to the compromised system.
3. The attacker renames rclone.exe to a less suspicious name (e.g., TrendFileSecurityCheck.exe) to evade detection based on process name.
4. The attacker uses rclone's copy or sync command to initiate data transfer to a remote cloud storage service such as Amazon S3 or a web server accessible via HTTP.
5. The attacker uses the --include flag to specify the file types to be exfiltrated (e.g., documents, source code, or databases).
6. The attacker may use the --transfers flag to increase the number of parallel transfers, speeding up the exfiltration process.
7. The attacker sets up a cron job to run rclone periodically, ensuring continuous exfiltration of data.
8. The data is exfiltrated to the attacker's controlled cloud storage, completing the objective.

Impact

Successful exploitation can lead to the exfiltration of sensitive company data, including intellectual property, financial records, or customer data. This data breach can result in financial losses, reputational damage, legal liabilities, and loss of competitive advantage. While the number of victims and sectors are unknown, the consequences of a successful data exfiltration can be severe for any organization.

Recommendation

• Deploy the Sigma rule "Potential Data Exfiltration via Rclone" to your SIEM and tune for your environment to detect suspicious rclone activity based on process names and command-line arguments.
• Implement the Sigma rule "Rclone Process Without Standard Path" to alert when rclone is executed from non-standard directories, which could indicate a renamed or moved copy of the tool.
• Investigate any processes where process.pe.original_file_name is rclone.exe but the process name is different, indicating a possible attempt to evade detection as described in the Overview.
• Review rclone command-line arguments for usage of copy or sync commands in conjunction with --include or --exclude flags to identify potentially targeted data as noted in the Triage section.
• Monitor process creation events (Sysmon Event ID 1) for the execution of rclone.exe or renamed copies with unusual command-line arguments, using the provided log source details.