# Cl0p Ransomware Group
Cl0p is the threat actor responsible for the largest single data theft campaign in recorded history. In May 2023, they exploited a previously unknown SQL injection vulnerability in Progress Software's MOVEit Transfer platform, compromised more than 2,700 organizations before the vulnerability was publicly disclosed, exfiltrated sensitive data from all of them, and then demanded ransom payments from each victim under threat of publishing the stolen data. The MOVEit campaign affected more than 90 million individuals worldwide, including employees of federal government agencies, students at major universities, patients at healthcare systems, and customers of financial services firms. Estimated total impact exceeds $10 billion by some financial analyses.
The name Cl0p uses a zero in place of the letter O, a stylistic convention common in cybercriminal naming that also reflects the group's Eastern European, specifically Russian-speaking, operator base. The group has been active since approximately 2014 under various designations. Mandiant and Microsoft track overlapping activity through FIN11 and TA505, respectively. Microsoft's current naming convention designates the ransomware-deployment and extortion operations as Lace Tempest. The relationships between Cl0p the ransomware, TA505 the broader criminal organization, and FIN11 the Mandiant designation reflect genuine organizational overlap rather than simple renaming: Cl0p appears to be the extortion capability deployed by an actor cluster that also conducted banking malware operations, spam campaigns, and dridex distribution under the TA505 umbrella.
Cl0p's most significant innovation is not a technical capability but a business model. They identified that managed file transfer platforms occupy a uniquely valuable position in enterprise data flows: organizations use them specifically to transmit the most sensitive data, HR records, legal documents, financial reports, healthcare information, and compliance materials. A single zero-day in one of these platforms simultaneously exposes the crown jewel data of every organization running it. The ROI on developing or acquiring a single exploit is measured not in the data of one organization but in the extortion potential against hundreds or thousands of organizations simultaneously.
The attribution of Cl0p to Russian-speaking criminal operators rests on multiple independent lines of evidence. The malware code contains artifacts suggesting Russian-language development environments. The group avoids targeting organizations in Commonwealth of Independent States (CIS) countries, a characteristic pattern of Russian-speaking criminal groups who operate with implicit or explicit tolerance from Russian authorities on the condition that they do not create diplomatic problems by attacking Russian or allied targets. Law enforcement actions have produced arrests of Cl0p-affiliated individuals in Ukraine, confirming Eastern European operations, though the primary operators have not been arrested.
In June 2021, Ukrainian law enforcement, operating in coordination with South Korean authorities and the US FBI, arrested six individuals connected to Cl0p ransomware operations in Ukraine and seized approximately $185,000 in cash, computer equipment, and vehicles. The arrests disrupted some operations temporarily but did not eliminate the group, which resumed activity within months with increased operational security.
The TA505/FIN11 organizational context is important for understanding Cl0p's capabilities. TA505, active since at least 2014, operated as one of the largest spam and banking malware distribution networks in the world, sending hundreds of millions of malicious emails and distributing Dridex banking malware at industrial scale. The organization's infrastructure, financial resources, and operational experience provided the foundation for increasingly sophisticated targeted operations under the FIN11 designation, culminating in the Cl0p extortion campaigns that represent the current evolution of the group's capabilities.
CISA designated the Cl0p ransomware group a "Threat Actor of Particular Concern" following the MOVEit campaign in 2023, and the US State Department's Rewards for Justice program offered up to $10 million for information leading to the identification of individuals directing Cl0p operations against US critical infrastructure.
Cl0p's significance extends beyond the scale of individual campaigns. They represent the maturation of a threat model that exploits the architecture of enterprise software procurement and deployment: organizations deploy the same software products, those products contain vulnerabilities, and a single zero-day enables simultaneous access to every organization running a vulnerable version before any of them can patch.
The managed file transfer sector proved to be an exceptionally high-value target class. Accellion File Transfer Appliance, Fortra GoAnywhere MFT, and Progress MOVEit Transfer each represent the same data flow architecture: sensitive documents from multiple business units and external partners converge on a single managed transfer platform. Security teams patch external-facing web applications, but MFT platforms often fall into a governance gap, managed by IT operations rather than security, running on older configurations, and rarely subject to the continuous vulnerability scanning that customer-facing applications receive.
The scale of downstream harm in the MOVEit campaign illustrates the amplification effect of third-party software exploitation. The US Department of Energy, the US Department of Health and Human Services, the Louisiana Office of Motor Vehicles (exposing 6 million residents' records), the Oregon Department of Transportation (exposing 3.5 million records), Shell, British Airways, the BBC, PricewaterhouseCoopers, Ernst and Young, Siemens Energy, Sony, and hundreds of other organizations were compromised not because their own security programs failed but because a vendor they trusted had a critical vulnerability in widely deployed software. The Orbital Alliance Framework (OAF) threat scenario is precisely this: a trusted software vendor becomes the entry point for an adversary that none of the affected organizations ever directly faced.
The extortion model without encryption also eliminated a traditional defensive option. Organizations that maintain comprehensive, air-gapped backups can recover from ransomware encryption without paying. They cannot unilaterally prevent publication of stolen data. Cl0p's pivot to data-theft extortion in the file transfer campaigns reflects awareness that backup discipline has improved enough to reduce the leverage of encryption-based ransomware against well-prepared organizations.
Cl0p's technical approach in the file transfer campaigns differs substantially from conventional ransomware operations, which typically involve credential compromise, lateral movement, and network-wide encryption. The file transfer zero-day model is more surgical and more scalable.
T1190: Exploit Public-Facing Application. All three major Cl0p file transfer campaigns began with exploitation of a known but unreported vulnerability in the target application. CVE-2021-27101 through CVE-2021-27104 in Accellion FTA were SQL injection and OS command injection vulnerabilities. CVE-2023-0669 in Fortra GoAnywhere MFT was a remote code execution vulnerability in the administrative interface. CVE-2023-34362 in Progress MOVEit Transfer was a SQL injection vulnerability in the web application that enabled unauthorized database access and file retrieval. In each case, Cl0p developed or acquired the exploit prior to public disclosure, confirmed by the timeline of compromises beginning before vendors issued patches.
T1505.003: Server Software Component (Web Shell). Following initial exploitation, Cl0p deployed web shells on compromised servers. In the MOVEit campaign, the web shell LEMURLOOT was installed on victim MOVEit Transfer servers. LEMURLOOT authenticated with a hardcoded password, enumerated the victim's MOVEit database structure, retrieved stored files, and reported system configuration information back to Cl0p infrastructure. The web shell enabled persistent access even if the underlying SQL injection vulnerability was subsequently patched.
T1119: Automated Collection. The simultaneous compromise of thousands of organizations required automated data collection processes rather than manual interaction with each victim. Cl0p's tooling automated the connection to each compromised MFT server, enumerated stored files, identified high-value data categories, and staged files for exfiltration without operator intervention for each individual victim. This automation is what made the simultaneous compromise of 2,700 organizations operationally feasible.
T1567: Exfiltration Over Web Service. Stolen data was exfiltrated through standard HTTPS connections, blending with normal MFT platform traffic. The timing of exfiltration, shortly after each compromise was established, preceded vendor notification and patch issuance in most cases, meaning that data was already exfiltrated before organizations received any public warning about the vulnerability.
T1486: Data Encrypted for Impact. In earlier Cl0p operations predating the file transfer pivot (2020 and prior), the group deployed conventional file-encrypting ransomware on victim networks following lateral movement. The healthcare sector attacks in 2020 and 2021 used encryption alongside data theft. The transition to data-theft-only extortion in the Accellion, GoAnywhere, and MOVEit campaigns reflects operational efficiency: encryption requires broad network access and extended dwell time, while web shell-based MFT exploitation achieves the data theft objective in hours without the detection risk of lateral movement.
Victim Extortion Process. Following each campaign, Cl0p publishes a portion of stolen data on their Tor-hosted leak site as proof of possession, then contacts victim organizations directly with ransom demands. In the MOVEit campaign, demands ranged from hundreds of thousands to millions of dollars per victim depending on organization size and data sensitivity. Chainalysis estimated that approximately $75 million in ransom payments were made in connection with the MOVEit campaign as of late 2023, representing only a fraction of the affected organizations but a substantial criminal revenue event.
Timeline Precision in the MOVEit Campaign. Cl0p began exploiting CVE-2023-34362 on or around May 27, 2023, the Saturday of Memorial Day weekend in the United States. The timing choice reflects deliberate operational planning: IT and security teams are understaffed on holiday weekends, incident detection is slower, and the window between initial exploitation and incident response is wider. By the time Progress Software disclosed the vulnerability and released a patch on May 31, Cl0p had already completed mass exploitation of the vulnerable population.
Cl0p's attack model maps directly across four PDM domains, and each domain provides a different layer of the defensive response.
VSD: Vulnerability and Surface Defense (Primary Prevention Domain). The Continuous Surface Reduction (CSR) methodology, "Every surface you expose is a surface we eliminate," treats external-facing applications as an attack surface that must be inventoried, continuously scanned, and prioritized for patching. Managed file transfer platforms are external-facing by design: they accept connections from external partners and deliver files from internal systems to external recipients. Any MFT deployment represents an external surface, and the vulnerability management program must treat it as such. VSD-V01 (external attack surface discovery and continuous scanning) is the foundational mission response. Organizations that conduct continuous web application scanning against their MFT deployments would detect known CVEs before Cl0p exploits them and reduce their exposure window even for zero-days by detecting anomalous activity on the platform.
The network segmentation dimension of VSD is equally critical. MFT platforms, by their function, have access to sensitive data repositories across multiple business units. Network segmentation that limits the blast radius of MFT compromise, preventing a compromised MFT server from accessing data stores beyond its operational scope, is a required architectural control. VSD-V03 (network segmentation validation) applies directly.
DPS: Data Protection and Sovereignty. The Sovereign Data Protocol (SDP) principle, "Your data lives where you decide. Period," confronts the Cl0p model directly. Organizations that store sensitive data on MFT platforms without encryption at the application layer expose that data to any actor who achieves access to the MFT server. Files transferred through MFT platforms should be encrypted with keys that the MFT platform itself does not hold. When Cl0p deployed LEMURLOOT and automated data collection, they retrieved files in whatever state they existed on the MFT server: unencrypted and accessible. Application-layer encryption using customer-held keys would have reduced the value of every exfiltrated file to ciphertext without a key. DPS-S02 (data classification and encryption-at-rest standards) is the directly applicable mission.
TID: Threat Intelligence and Defense. The Cl0p campaigns all followed a detectable pattern before the vulnerability was publicly disclosed. Web shell deployment produces server-side file system artifacts. Automated data collection produces anomalous query patterns in database logs. Unusual file access patterns on MFT servers, particularly bulk file reads initiated by unexpected process identifiers, are detectable through MFT server logging if that logging is enabled, collected, and monitored. The LEMURLOOT web shell used in the MOVEit campaign authenticated with a hardcoded string that could have been detected by web application firewall rules or file integrity monitoring on the MOVEit application directory. TID-R02 (TTP-based detection rule development) should include Cl0p-specific indicators across all three MFT platforms they have targeted, because the web shell deployment pattern and automated collection behavior are consistent across campaigns.
RGA: Risk Governance and Assurance. The downstream regulatory and legal consequences of Cl0p compromise are severe and frequently underestimated. The MOVEit campaign triggered breach notification obligations under HIPAA for healthcare entities, GLBA for financial institutions, state consumer protection laws across nearly every US state, and GDPR for organizations processing EU personal data. The Louisiana OMV disclosure, affecting 6 million state residents' driver's license data, triggered a state-level emergency response. Organizations that use third-party MFT vendors are not relieved of breach notification obligations because the vendor was compromised: the data was theirs, and the notification obligation attaches to the data. The Perpetual Compliance Assurance (PCA) methodology requires that incident response plans include vendor compromise scenarios with pre-established notification workflows, legal review processes, and regulatory filing templates. RGA-C01 (breach notification compliance program) is the directly applicable mission. Organizations should complete this preparation before they need it, not after Cl0p's extortion notice arrives.
Cl0p industrialized mass exploitation of enterprise software vulnerabilities and demonstrated that the managed file transfer sector was an unguarded high-value target class. The MOVEit campaign compromised more than 2,700 organizations and affected more than 90 million individuals from a single zero-day. No individual victim organization could have prevented the vulnerability in the vendor's product.
What organizations can control is the attack surface, the data sensitivity of what the MFT platform can access, the monitoring depth applied to MFT server behavior, and the incident response readiness for a third-party compromise scenario. Organizations that completed these controls before May 2023 would have detected anomalous web shell activity, limited the data available for exfiltration through application-layer encryption, and entered the incident response phase with established notification playbooks rather than building them under active extortion pressure.
The data-theft extortion model eliminates the backup-based recovery option that reduced ransomware leverage for well-prepared organizations. There is no technical control that reverses data exfiltration after it occurs. Prevention, through vulnerability management and access control, and detection, through MFT server behavioral monitoring, are the only effective response windows.
Cl0p continues to operate. Their demonstrated willingness to invest in zero-day development or acquisition for high-ROI target platforms means that future campaigns against other widely deployed enterprise software are probable. Any organization running software that handles sensitive data transfers at scale should treat Cl0p's targeting model as a persistent threat to their vendor's attack surface.