Potential Data Exfiltration via Rclone

Attackers are leveraging Rclone, a legitimate command-line program to manage files on cloud storage, for malicious purposes. The primary abuse case involves renaming Rclone (e.g., to TrendFileSecurityCheck.exe) to evade detection based on process name. Once renamed, attackers use Rclone’s copy/sync functionalities with cloud backends like S3 or HTTP endpoints. They often employ --include filters to target specific sensitive file types for exfiltration. This activity is frequently blended with regular administrative traffic to further obfuscate the malicious intent. Defenders should be aware of this tactic, particularly when unusual processes are observed interacting with cloud storage services.

Attack Chain

1. The attacker gains initial access to the system through an undisclosed method.
2. Rclone is downloaded or transferred to the victim machine.
3. The rclone executable is renamed to a benign-sounding name (e.g., TrendFileSecurityCheck.exe) to masquerade as a legitimate system utility.
4. The attacker configures rclone to connect to a cloud storage backend (e.g., an S3 bucket or HTTP endpoint) controlled by the attacker.
5. A command is executed using the renamed rclone executable, specifying the copy or sync command.
6. The command includes --include flags to filter and select specific file types (e.g., documents, source code, databases) for exfiltration.
7. Rclone transfers the targeted files from the victim machine to the attacker’s cloud storage backend, potentially using the --transfers option for faster exfiltration.
8. The attacker accesses the exfiltrated data from their cloud storage.

Impact

Successful exploitation can lead to the exfiltration of sensitive data, including proprietary information, customer data, financial records, or intellectual property. The impact can range from reputational damage and financial losses to legal and regulatory repercussions. The scope of damage depends on the sensitivity and volume of the exfiltrated data, the number of affected systems, and the effectiveness of the attacker’s filtering criteria.

Recommendation

• Deploy the Sigma rule Suspicious Rclone Usage to detect renamed rclone executables executing copy/sync commands.
• Enable Sysmon process creation logging (Event ID 1) to collect the necessary process execution data for the Sigma rules.
• Investigate any process identified by the Sigma rule Suspicious Rclone Usage by examining command-line arguments for cloud backend destinations and --include filters.
• Monitor network connections for unusual outbound traffic to cloud storage providers (AWS S3, Azure Blob Storage, Google Cloud Storage) from processes other than approved backup solutions.
• Implement application control policies to restrict the execution of unauthorized or renamed executables.