Table of Contents
CLOP ransomware, also known as Cl0p, is a significant cyber threat that has impacted organizations globally. This ransomware strain, operated by the cybercriminal group TA505 (among other aliases), has evolved from encrypting files to primarily focusing on data exfiltration and extortion. This article provides a comprehensive analysis of CLOP, including its origins, tactics, targets, attack campaigns, and, most importantly, defense strategies for security professionals. Recent high-profile activity, particularly the exploitation of vulnerabilities in managed file transfer (MFT) solutions like MOVEit Transfer, GoAnywhere MFT, and Accellion FTA, underscores the urgent need for robust defenses against this persistent threat. You can also read about 5 challenges of cyber security.
Origins & Evolution
CLOP ransomware first emerged in February 2019 as a variant of the CryptoMix ransomware family. It is believed to be operated by a Russian-speaking cybercriminal group, often associated with the threat actor TA505 (also tracked as FIN11, and other aliases). This group operates a Ransomware-as-a-Service (RaaS) model, making CLOP available to affiliates on dark web forums.
Early Tactics (2019): Initially, CLOP employed digitally signed binaries to evade detection and targeted a wide range of industries. The ransomware encrypted files, appending the ".clop" extension (and variants like ".Cllp", ".Cl0p").
Shift to Double Extortion (2020): CLOP adopted the double extortion tactic, stealing sensitive data before encryption and threatening to publish it on a dedicated leak site ("CL0P^_- LEAKS") if the ransom was not paid.
Zero-Day Exploitation (2020-Present): A defining characteristic of CLOP's evolution has been its focus on exploiting zero-day vulnerabilities, particularly in file transfer software. This has allowed them to compromise numerous organizations simultaneously and exfiltrate large amounts of data. Key examples include:
Accellion FTA (2020-2021): Exploitation of multiple zero-days (CVE-2021-27101, CVE-2021-27102, CVE-2021-27103, CVE-2021-27104) led to breaches at numerous companies.
GoAnywhere MFT (January 2023): Exploitation of CVE-2023-0669 impacted over 130 organizations.
MOVEit Transfer (May 2023): Exploitation of a SQL injection vulnerability (CVE-2023-34362) resulted in a massive data theft campaign, affecting hundreds of organizations worldwide. Learn more about MOVEit breach.
Cleo Software (2024): Exploitation of zero-day (CVE-2024-50623) allowed for remote code execution and data theft.
Exploitation of vulnerabilities in Cleo's LexiCom, VLTrader, and Cleo Harmony products.
"Encryption-less Ransomware" (2023-Present): In many recent campaigns, CLOP has prioritized data exfiltration over encryption. This shift indicates a focus on maximizing financial gain through extortion, even if it means potentially impacting fewer victims.
CIS Exclusion: CLOP avoids targets in former Soviet countries and computers operating primarily in Russian.
Tactics & Techniques
CLOP's operations involve a multi-stage attack process, leveraging various tools and techniques. The group's TTPs are well-documented and mapped to the MITRE ATT&CK framework:
Initial Access:
Exploit Public-Facing Application (T1190): CLOP's primary method, exploiting vulnerabilities in software like MOVEit Transfer, GoAnywhere MFT, and Accellion FTA.
Phishing (T1566): Historically, CLOP used phishing campaigns with malicious attachments (macro-enabled documents) or links to downloaders like Get2, leading to the deployment of SDBOT, FlawedAmmyy, and Cobalt Strike. Learn more about types of phishing attacks.
Execution:
Command and Scripting Interpreter (T1059): CLOP uses PowerShell (T1059.001) and Windows Command Shell (T1059.003) for various tasks.
Shared Modules (T1129): Loading of malicious DLLs.
Persistence:
Web Shell (T1505.003): Installation of web shells like LEMURLOOT (MOVEit) and DEWMODE (Accellion) to maintain access.
Application Shimming (T1547.006): Used by SDBot for persistence.
Privilege Escalation:
Exploitation for Privilege Escalation (T1068): Leveraging vulnerabilities to gain higher privileges. More about privilege escalation attack.
Defense Evasion:
Process Injection (T1055): Used for injecting malicious code.
Indicator Removal (T1070): Deleting logs and other evidence.
DLL Side-Loading (T1574.002): Loading malicious DLLs by exploiting legitimate applications.
Discovery:
Remote System Discovery (T1018): Identifying other systems on the network.
Lateral Movement:
SMB/Windows Admin Shares (T1021.002): Moving laterally using shared folders.
Remote Desktop Protocol (T1021.001): Hijacking RDP sessions.
Collection:
Screen Capture (T1113): Taking screenshots.
Data Staged (T1074): Collecting and preparing data for exfiltration.
Command and Control:
Application Layer Protocol (T1071): Using standard protocols for communication.
Ingress Tool Transfer (T1105): Downloading additional tools.
Exfiltration:
Exfiltration Over C2 Channel (T1041): Stealing data using the established command and control channel.
Exfiltration Over Web Service (T1567): Often using cloud storage like megaupload.
Impact:
Data Encrypted for Impact (T1486): CLOP ransomware encrypts files.
Data Destruction(T1485): CLOP deletes the original files after encryption.
Malware Toolkit: TA505, associated with CLOP, utilizes a diverse toolkit:
FlawedAmmyy/FlawedGrace RAT: Information collection, C2 communication, downloads other malware.
SDBot RAT: Infection propagation, vulnerability exploitation, application shimming.
Truebot: First-stage downloader, system information collection, screenshot capture, downloads FlawedGrace or Cobalt Strike.
Cobalt Strike: Network access after Active Directory compromise.
DEWMODE: Web shell for Accellion FTA.
LEMURLOOT: Web shell for MOVEit Transfer (authenticates with a hardcoded password, steals data, manages users).
Torrents: CLOP utilizes torrents for leaking stolen data, making it more difficult for authorities to shut down their operations.
Targets or Victimology
CLOP's primary motivation is financial gain, targeting organizations with the ability to pay substantial ransoms. They have demonstrated a "big game hunting" approach, focusing on large enterprises, but have also impacted smaller organizations.
Industries: CLOP has targeted a wide range of industries, including:
Financial Services
Healthcare
Manufacturing
Education
Technology
Retail
Transportation
Energy
Government
Legal
Regions: CLOP operates globally, but recent campaigns have heavily impacted North America and Europe (particularly the United States).
Impact: CLOP attacks can lead to:
Data breaches (leak of sensitive customer, employee, and business data).
Operational disruption (downtime of critical systems and services).
Financial losses (ransom payments, recovery costs, legal fees, reputational damage).
Regulatory fines (for non-compliance with data protection regulations).
Attack Campaigns
Several significant attack campaigns highlight CLOP's impact and evolving tactics:
Accellion FTA Exploitation (2020-2021): CLOP exploited multiple zero-day vulnerabilities in Accellion's legacy File Transfer Appliance (FTA), affecting numerous organizations, including Kroger, Singtel, QIMR Berghofer Medical Research Institute, Reserve Bank of New Zealand, ASIC, and the Office of the Washington State Auditor. This campaign marked a shift towards data exfiltration and double extortion.
GoAnywhere MFT Exploitation (January 2023): CLOP exploited CVE-2023-0669, a remote code execution vulnerability in Fortra's GoAnywhere MFT, impacting approximately 130 victims.
MOVEit Transfer Exploitation (May 2023 - Present): This is CLOP's most significant campaign to date. They exploited CVE-2023-34362, a SQL injection vulnerability in Progress Software's MOVEit Transfer, leading to the mass exfiltration of data from hundreds of companies. Victims include BBC, British Airways, Estee Lauder companies, 1st Source, First National Bankers Bank (USA), Putnam Investments (USA), Landal Greenparks (Netherlands), Shell (UK), the New York City Department of Education, and Ernst & Young. This campaign is projected to have earned CLOP $75-100 million.
Cleo Software Exploitation (2024 - Present): CLOP exploited a zero-day vulnerability (CVE-2024-50623) in Cleo's LexiCom, VLTrader, and Harmony products, impacting dozens of organizations. This campaign demonstrated a continued focus on file transfer software and a shift towards data theft without encryption.
Other Notable Victims: Shell, Qualys, Kroger, University of Colorado, University of Miami, Stanford Medicine, University of Maryland Baltimore (UMB), University of California.
Defenses
Protecting against CLOP ransomware requires a multi-layered approach, combining proactive security measures, robust detection capabilities, and a well-defined incident response plan. Generic defense strategies, combined with CLOP-specific mitigations, are essential:
Vulnerability Management & Patching: This is crucial given CLOP's reliance on exploiting vulnerabilities. Prioritize patching internet-facing systems, especially file transfer software (MOVEit, GoAnywhere, Accellion, etc.). Implement a robust vulnerability assessments program with regular scanning and rapid patching.
Software Updates: Keep all software, OS, and server software up-to-date with the latest security patches (especially VPN solutions). Automate updates.
Network Segmentation: Isolate critical systems and data from less critical networks to prevent lateral movement. This limits the impact of a successful breach.
Endpoint Detection and Response (EDR): Deploy EDR solutions on all endpoints to detect and respond to malicious activity. Look for EDR tools with strong behavioral analysis capabilities.
Security Awareness Training: Educate employees about phishing attacks, social engineering tactics, and safe browsing habits. Regular training and simulated phishing exercises are vital. More about phishing simulation.
Multi-Factor Authentication (MFA): Enforce MFA for all user accounts, especially for remote access and privileged accounts.
Data Backup and Recovery: Implement a robust backup and recovery strategy. Maintain offline backups (encrypted and immutable) and regularly test the restoration process.
Least Privilege Principle: Restrict user access to only the resources they need to perform their job duties. This limits the potential damage from compromised accounts.
Web Application Firewalls (WAFs): Deploy WAFs to protect web applications from attacks, including SQL injection (crucial for preventing MOVEit-style exploits).
Threat Intelligence: Stay informed about the latest CLOP TTPs, IOCs, and vulnerabilities. Use threat intelligence feeds to enhance detection and prevention capabilities. What is threat intelligence?
Incident Response Plan: Develop and regularly test a comprehensive incident response plan that includes procedures for containing, eradicating, and recovering from a ransomware attack.
Network Monitoring: Implement continuous network monitoring to detect suspicious activity, including unusual data transfers, communication with known malicious IP addresses, and attempts to disable security controls. Utilize tools to detect abnormal activity and lateral movement.
Email Security: Employ robust email security gateways to filter out phishing emails, block malicious attachments, and scan for malicious links. Implement email banners to identify external emails. More about email authentication.
YARA Rules: Utilize YARA rules, such as those provided by CISA, to detect CLOP-related malware samples. Keep YARA rules updated.
Disable Unused Ports.
Antivirus: Install, update, and enable real-time detection with antivirus software.
Specific to MOVEit Transfer (CVE-2023-34362):
Apply the official patch from Progress Software.
Monitor for the presence of the LEMURLOOT web shell (using YARA rules or file integrity monitoring).
Audit administrative accounts in the MOVEit database (using the SQL query provided by CISA).
Review logs for suspicious activity.
Specific to GoAnywhere MFT (CVE-2023-0669):
Apply the official patch from Fortra.
Monitor for indicators of compromise related to this vulnerability.
Specific to Cleo Software Vulnerability (CVE-2024-50623, CVE-2024-55956):
Apply updates (Version 5.8.0.21)
Monitor for exploitation attempts.
Conclusion
CLOP ransomware remains a significant and evolving threat, demonstrating a clear shift towards data exfiltration and extortion over traditional encryption. The group's exploitation of zero-day vulnerabilities in widely used file transfer software has resulted in massive data breaches and significant financial losses for organizations worldwide. To effectively combat CLOP, organizations must prioritize vulnerability management, implement robust security controls, and maintain a proactive security posture. Staying informed about CLOP's latest tactics and leveraging threat intelligence are crucial for minimizing risk and mitigating the potential impact of this persistent cyber threat. The emphasis on data exfiltration highlights the critical need for strong data loss prevention (DLP) strategies and robust access controls to protect sensitive information. Stay up-to-date on the latest cybersecurity news to remain secure.
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Arun KL
Arun KL is a cybersecurity professional with 15+ years of experience in IT infrastructure, cloud security, vulnerability management, Penetration Testing, security operations, and incident response. He is adept at designing and implementing robust security solutions to safeguard systems and data. Arun holds multiple industry certifications including CCNA, CCNA Security, RHCE, CEH, and AWS Security.
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