Detecting Rclone Execution with Network Activity for Data Exfiltration

This threat brief focuses on detecting the malicious use of rclone, a legitimate command-line tool designed for syncing files to and from various cloud storage providers. While rclone serves a valid purpose in many IT environments, it has been widely co-opted by threat actors as a versatile tool for data exfiltration and cloud abuse. This detection specifically targets the execution of rclone.exe combined with command-line arguments that strongly suggest malicious intent, such as operations involving suspicious remote targets (e.g., remote:, mega:, ftp:) and flags that facilitate stealthy or automated transfers (--transfers, --ignore-existing, --auto-confirm). The detection leverages network visibility module logs, particularly flow data from Cisco Network Visibility Module, to identify processes initiating network connections with these characteristics. The widespread abuse of rclone by various ransomware and extortion groups, including affiliates of Sodinokibi/REvil and BazarLoader campaigns, underscores the critical need for robust detection at the endpoint and network layers.

Attack Chain

1. Initial Compromise: A threat actor gains unauthorized access to an endpoint within the target network through various means, such as exploitation of vulnerabilities, phishing, or credential theft.
2. Tool Deployment: The threat actor deploys the rclone utility onto the compromised system, either by directly downloading it from a public repository or transferring it laterally from another compromised host.
3. Configuration for Remote Transfer: The attacker configures rclone or executes it with command-line arguments that specify an attacker-controlled remote cloud storage service (e.g., remote:, mega:, ftp:, ftp1:).
4. Initiate Data Exfiltration: rclone.exe is executed with specific arguments to initiate data transfer, such as copy, combined with a local path and the previously configured remote target.
5. Automated/Stealthy Transfer: The attacker may include flags like --transfers, --ignore-existing, and --auto-confirm to speed up the transfer, bypass existing files, and reduce interactive prompts, facilitating stealthier and automated exfiltration.
6. Network Connection for Exfiltration: rclone establishes outbound network connections to the specified cloud storage provider, utilizing standard protocols like HTTP/S or FTP, which might blend in with legitimate network traffic.
7. Data Transfer and Completion: The utility successfully transfers sensitive data from the compromised system to the attacker-controlled cloud storage, achieving the exfiltration objective.

Impact

Successful exploitation involving rclone results in the unauthorized exfiltration of sensitive organizational data to attacker-controlled cloud storage. This can lead to severe consequences, including intellectual property theft, exposure of personally identifiable information (PII) or protected health information (PHI), regulatory non-compliance fines, reputational damage, and financial losses due to extortion attempts or competitive disadvantage. The use of legitimate tools like rclone makes detection challenging, allowing attackers to remain undetected for longer periods, potentially exfiltrating larger volumes of critical data. Organizations across all sectors are at risk, with specific targeting often driven by the value of their data.

Recommendation

• Deploy the Sigma rule provided in this brief to your SIEM and tune for your environment to detect suspicious rclone activity.
• Ensure Cisco Network Visibility Module logs, specifically flow data, are properly ingested and configured in your SIEM environment, as indicated in the logsource of the detection rule.
• Review legitimate uses of rclone within your organization and create baselines or allowlists for known-good operational usage to reduce falsepositives.
• Monitor network_connection logs for outbound connections initiated by rclone.exe or other processes exhibiting similar command-line arguments as detailed in the detection section.
• Implement strong egress filtering to restrict outbound connections to only necessary and approved destinations, especially for cloud storage services.