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SUMMARY

Note: this joint Cybersecurity Advisory (CSA) is part of an ongoing #StopRansomware effort to publish advisories for network defenders that detail various ransomware variants and ransomware threat actors. These #StopRansomware advisories include recently and historically observed tactics, techniques, and procedures (TTPs) and indicators of compromise (IOCs) to help organizations protect against ransomware. Visit stopransomware.gov to see all #StopRansomware advisories and to learn more about other ransomware threats and no-cost resources.

Actions to take today to mitigate cyber threats from CL0P ransomware: 

• Take an inventory of assets and data, identifying authorized and unauthorized devices and software.


• Grant admin privileges and access only when necessary, establishing a software allow list that only executes legitimate applications.


• Monitor network ports, protocols, and services, activating security configurations on network infrastructure devices such as firewalls and routers.


• Regularly patch and update software and applications to their latest versions, and conduct regular vulnerability assessments.

The Federal Bureau of Investigation (FBI) and the Cybersecurity and Infrastructure Security Agency (CISA) are releasing this joint CSA to disseminate known CL0P ransomware IOCs and TTPs identified through FBI investigations as recently as June 2023.

According to open source information, beginning on May 27, 2023, CL0P Ransomware Gang, also known as TA505, began exploiting a previously unknown SQL injection vulnerability (CVE-2023-34362) in Progress Software's managed file transfer (MFT) solution known as MOVEit Transfer. Internet-facing MOVEit Transfer web applications were infected with a web shell named LEMURLOOT, which was then used to steal data from underlying MOVEit Transfer databases. In similar spates of activity, TA505 conducted zero-day-exploit-driven campaigns against Accellion File Transfer Appliance (FTA) devices in 2020 and 2021, and Fortra/Linoma GoAnywhere MFT servers in early 2023.

FBI and CISA encourage organizations to implement the recommendations in the Mitigations section of this CSA to reduce the likelihood and impact of CL0P ransomware and other ransomware incidents.

Download the PDF version or the STIX file of this report:

TECHNICAL DETAILS

Note: This advisory uses the MITRE ATT&CK® for Enterprise framework, version 13. See MITRE ATT&CK for Enterprise for all referenced tactics and techniques.

Appearing in February 2019, and evolving from the CryptoMix ransomware variant, CL0P was leveraged as a Ransomware as a Service (RaaS) in large-scale spear-phishing campaigns that used a verified and digitally signed binary to bypass system defenses. CL0P was previously known for its use of the "double extortion" tactic of stealing and encrypting victim data, refusing to restore victim access and publishing exfiltrated data on Tor via the CL0P^_-LEAKS website. In 2019, TA505 actors leveraged CL0P ransomware as the final payload of a phishing campaign involving a macro-enabled document that used a Get2 malware dropper for downloading SDBot and FlawedGrace. In recent campaigns beginning 2021, CL0P preferred to rely mostly on data exfiltration over encryption.

Beyond CL0P ransomware, TA505 is known for frequently changing malware and driving global trends in criminal malware distribution. Considered to be one of the largest phishing and malspam distributors worldwide, TA505 is estimated to have compromised more than 3,000 U.S.-based organizations and 8,000 global organizations.

TA505 has operated:

• A RaaS and has acted as an affiliate of other RaaS operations,


• As an initial access broker (IAB), selling access to compromised corporate networks,


• As a customer of other IABs,


• And as a large botnet operator specializing in financial fraud and phishing attacks.

In a campaign from 2020 to 2021, TA505 used several zero-day exploits to install a web shell named DEWMODE on internet-facing Accellion FTA servers. Similarly, the recent exploitation of MOVEit Transfer, a SQL injection vulnerability was used to install the web shell, which enabled TA505 to execute operating system commands on the infected server and steal data.

In late January 2023, the CL0P ransomware group launched a campaign using a zero-day vulnerability, now catalogued as CVE-2023-0669, to target the GoAnywhere MFT platform. The group claimed to have exfiltrated data from the GoAnywhere MFT platform that impacted approximately 130 victims over the course of 10 days. Lateral movement into the victim networks from the GoAnywhere MFT was not identified, suggesting the breach was limited to the GoAnywhere platform itself. Over the next several weeks, as the exfiltrated data was parsed by the group, ransom notes were sent to upper-level executives of the victim companies, likely identified through open source research. The ransom notes threatened to publish the stolen files on the CL0P data leak site if victims did not pay the ransom amount.

CL0P's toolkit contains several malware types to collect information, including the following:

• FlawedAmmyy/FlawedGrace remote access trojan (RAT) collects information and attempts to communicate with the Command and Control (C2) server to enable the download of additional malware components [T1071], [T1105].


• SDBot RAT propagates the infection, exploiting vulnerabilities and dropping copies of itself in removable drives and network shares [T1105]. It is also capable of propagating when shared though peer-to-peer (P2P) networks. SDBot is used as a backdoor [T1059.001] to enable other commands and functions to be executed in the compromised computer. This malware uses application shimming for persistence and to avoid detection [T1546.011].


• Truebot is a first-stage downloader module that can collect system information and take screenshots [T1113], developed and attributed to the Silence hacking group. After connecting to the C2 infrastructure, Truebot can be instructed to load shell code [T1055] or DLLs [T1574.002], download additional modules [T1129], run them, or delete itself [T1070]. In the case of TA505, Truebot has been used to download FlawedGrace or Cobalt Strike beacons.


• Cobalt Strike is used to expand network access after gaining access to the Active Directory (AD) server [T1018].


• DEWMODE is a web shell written in PHP designed to target Accellion FTA devices and interact with the underlying MySQL database and is used to steal data from the compromised device [1505.003].


• LEMURLOOT is a web shell written in C# designed to target the MOVEit Transfer platform. The web shell authenticates incoming http requests via a hard-coded password and can run commands that will download files from the MOVEit Transfer system, extract its Azure system settings, retrieve detailed record information, and create, insert, or delete a particular user. When responding to the request, the web shell returns data in a gzip compressed format.

CVE-2023-34362 MOVEIT TRANSFER VULNERABILITY

MOVEit is typically used to manage an organization's file transfer operations and has a web application that supports MySQL, Microsoft SQL Server, and Azure SQL database engines. In May 2023, the CL0P ransomware group exploited a SQL injection zero-day vulnerability CVE-2023-34362 to install a web shell named LEMURLOOT on MOVEit Transfer web applications [T1190] [1]. The web shell was initially observed with the name human2.aspx in an effort to masquerade as the legitimate human.aspx file present as part of MOVEit Transfer software. Upon installation, the web shell creates a random 36 character password to be used for authentication. The web shell interacts with its operators by awaiting HTTP requests containing a header field named X-siLock-Comment, which must have a value assigned equal to the password established upon the installation of the web shell. After authenticating with the web shell, operators pass commands to the web shell that can:

• Retrieve Microsoft Azure system settings and enumerate the underlying SQL database.


• Store a string sent by the operator and then retrieve a file with a name matching the string from the MOVEit Transfer system.


• Create a new administrator privileged account with a randomly generated username and LoginName and RealName values set to "Health Check Service."


• Delete an account with LoginName and RealName values set to 'Health Check Service.'

Progress Software announced the discovery of CVE-2023-34362 MOVEit Transfer vulnerability and issued guidance on known affected versions, software upgrades, and patching. Based on evidence of active exploitation, CISA added this vulnerability to the Known Exploited Vulnerabilities (KEVs) Catalog on June 2, 2023. This MOVEit Transfer critical vulnerability exploit impacts the following versions of the software [2]:

• MOVEit Transfer 2023.0.0


• MOVEit Transfer 2022.1.x


• MOVEit Transfer 2022.0.x


• MOVEit Transfer 2021.1.x


• MOVEit Transfer 2021.0.x


• MOVEit Transfer 2020.1.x


• MOVEit Transfer 2020.0.x

Due to the speed and ease TA505 has exploited this vulnerability, and based on their past campaigns, FBI and CISA expect to see widespread exploitation of unpatched software services in both private and public networks. For IOCs related to the MOVEit campaign, see table 2.

DETECTION METHODS

Below, are open source deployable YARA rules that may be used to detect malicious activity of the MOVEit Transfer Zero Day Vulnerability. For more information, visit GitHub or the resource section of this CSA. [1] [3]:

If a victim rebuilds the web server but leaves the database intact, the CL0P user accounts will still exist and can be used for persistent access to the system.

Victims can use the following SQL query to audit for active administrative accounts, and should validate that only intended accounts are present.

SELECT * FROM [].[dbo].[users] WHERE Permission=30 AND Status='active' and Deleted='0'

MOVEit Campaign Indicators of Compromise

GoAnywhere Campaign Indicators of Compromise

MITRE ATT&CK TECHNIQUES

See tables below for referenced CL0P tactics and techniques used in this advisory.

MITIGATIONS

The authoring agencies recommend organizations implement the mitigations below to improve their organization's security posture in response to threat actors' activity. These mitigations align with the Cross-Sector Cybersecurity Performance Goals (CPGs) developed by CISA and the National Institute of Standards and Technology (NIST). The CPGs provide a minimum set of practices and protections that CISA and NIST recommend all organizations implement. CISA and NIST based the CPGs on existing cybersecurity frameworks and guidance to protect against the most common and impactful threats and TTPs. Visit CISA's Cross-Sector Cybersecurity Performance Goals for more information on the CPGs, including additional recommended baseline protections to reduce the risk of compromise by CL0P ransomware.

• Reduce threat of malicious actors using remote access tools by:
  
  • Auditing remote access tools on your network to identify currently used and/or authorized software.
  
  
  • Reviewing logs for execution of remote access software to detect abnormal use of programs running as a portable executable [CPG 2.T].
  
  
  • Using security software to detect instances of remote access software only being loaded in memory.
  
  
  • Requiring authorized remote access solutions only be used from within your network over approved remote access solutions, such as virtual private networks (VPNs) or virtual desktop interfaces (VDIs).
  
  
  • Blocking both inbound and outbound connections on common remote access software ports and protocols at the network perimeter.
  
  


• Implement application controls to manage and control execution of software, including allowlisting remote access programs.
  
  • Application controls should prevent installation and execution of portable versions of unauthorized remote access and other software. A properly configured application allowlisting solution will block any unlisted application execution. Allowlisting is important because antivirus solutions may fail to detect the execution of malicious portable executables when the files use any combination of compression, encryption, or obfuscation.
  
  


• Strictly limit the use of RDP and other remote desktop services. If RDP is necessary, rigorously apply best practices, for example [CPG 2.W]:
  
  • Audit the network for systems using RDP.
  
  
  • Close unused RDP ports.
  
  
  • Enforce account lockouts after a specified number of attempts.
  
  
  • Apply phishing-resistant multifactor authentication (MFA).
  
  
  • Log RDP login attempts.
  
  


• Disable command-line and scripting activities and permissions [CPG 2.N].


• Restrict the use of PowerShell, using Group Policy, and only grant to specific users on a case-by-case basis. Typically, only those users or administrators who manage the network or Windows operating systems (OSs) should be permitted to use PowerShell [CPG 2.E].


• Update Windows PowerShell or PowerShell Core to the latest version and uninstall all earlier PowerShell versions. Logs from Windows PowerShell prior to version 5.0 are either non-existent or do not record enough detail to aid in enterprise monitoring and incident response activities [CPG 1.E, 2.S, 2.T].


• Review domain controllers, servers, workstations, and active directories for new and/or unrecognized accounts [CPG 4.C].


• Audit user accounts with administrative privileges and configure access controls according to the principle of least privilege [CPG 2.E].


• Reduce the threat of credential compromise via the following:
  
  • Place domain admin accounts in the protected users' group to prevent caching of password hashes locally.
  
  
  • Refrain from storing plaintext credentials in scripts.
  
  


• Implement time-based access for accounts set at the admin level and higher [CPG 2.A, 2.E].

In addition, the authoring authorities of this CSA recommend network defenders apply the following mitigations to limit potential adversarial use of common system and network discovery techniques and to reduce the impact and risk of compromise by ransomware or data extortion actors: 

• Implement a recovery plan to maintain and retain multiple copies of sensitive or proprietary data and servers in a physically separate, segmented, and secure location (i.e., hard drive, storage device, the cloud).


• Maintain offline backups of data and regularly maintain backup and restoration (daily or weekly at minimum). By instituting this practice, an organization limits the severity of disruption to its business practices [CPG 2.R].


• Require all accounts with password logins (e.g., service account, admin accounts, and domain admin accounts) to comply with National Institute for Standards and Technology (NIST) standards for developing and managing password policies.
  
  • Use longer passwords consisting of at least eight characters and no more than 64 characters in length [CPG 2.B].
  
  
  • Store passwords in hashed format using industry-recognized password managers.
  
  
  • Add password user "salts" to shared login credentials.
  
  
  • Avoid reusing passwords [CPG 2.C].
  
  
  • Implement multiple failed login attempt account lockouts [CPG 2.G].
  
  
  • Disable password "hints."
  
  
  • Refrain from requiring password changes more frequently than once per year. Note: NIST guidance suggests favoring longer passwords instead of requiring regular and frequent password resets. Frequent password resets are more likely to result in users developing password "patterns" cyber criminals can easily decipher.
  
  
  • Require administrator credentials to install software.
  
  


• Require multifactor authentication for all services to the extent possible, particularly for webmail, virtual private networks, and accounts that access critical systems [<