MedusaLocker is a significant ransomware threat that has been impacting organizations globally since its emergence in September 2019. Operating as a Ransomware-as-a-Service (RaaS), MedusaLocker allows its developers to profit by sharing the proceeds of ransom payments with affiliates who deploy the malware. This article provides a deep technical dive into MedusaLocker, covering its origins, evolution, tactics, techniques, and procedures (TTPs), victimology, attack campaigns, and most importantly, effective defense strategies. The goal is to equip security professionals with the knowledge necessary to combat this persistent threat. It is critical to highlight the difference between “Medusa” and “MedusaLocker”. This article refers to MedusaLocker.
MedusaLocker first appeared in September 2019. Unlike some ransomware families with clear state affiliations, MedusaLocker's origins are less defined. There are no definitive public reports directly linking it to a specific nation-state or known advanced persistent threat (APT) group. However, the sophistication of the attacks, and the targeting of healthcare organizations during the COVID-19 pandemic, have prompted speculation about potential connections.
MedusaLocker has shown continuous evolution. Early versions primarily relied on spam campaigns for distribution. Later, the focus shifted to exploiting vulnerabilities in Remote Desktop Protocol (RDP). The ransomware has also adopted techniques to evade detection, such as restarting infected machines in safe mode and attempting to disable security software. While the ransom note suggests data exfiltration, in many analysis reports, it isn't a consistently observed behavior, differentiating it from some other ransomware families that engage in "double extortion."
MedusaLocker employs a range of tactics and techniques throughout the attack lifecycle, making it a complex and adaptable threat. Understanding these TTPs is crucial for effective detection and mitigation.
Initial Access:
Exploitation of Remote Services (T1133): MedusaLocker frequently exploits misconfigured or vulnerable RDP services, often using brute-force attacks to guess weak passwords.
Phishing (T1566): Spam email campaigns with malicious attachments (often disguised as legitimate documents) are also used to deliver the ransomware. You can read more about types of phishing attacks here.
Execution:
Command and Scripting Interpreter: PowerShell (T1059.001): MedusaLocker utilizes a batch file (qzy.bat
) to execute a PowerShell script (qzy.txt
). This script contains the embedded, Base64-encoded MedusaLocker payload. The PowerShell script employs the "Invoke-ReflectivePEInjection" technique (from the PowerSploit framework) to load the ransomware directly into memory, avoiding writing the executable to disk initially.
Windows Management Instrumentation (WMIC): WMIC is used to delete volume shadow copies (wmic.exe Shadowcopy Delete
), hindering data recovery efforts. The copy in %AppData%\Roaming
as either svhost.exe
or svchostt.exe
.
Persistence:
Scheduled Task/Job (T1053.005): A scheduled task named svhost
(or svchostt
) is created to run the ransomware executable (copied to %AppData%\Roaming\
) every 15 minutes, ensuring persistence even after a reboot.
Registry Run Keys / Startup Folder (T1547.001): Registry entries are often modified to ensure the ransomware executes at system startup. To know more about windows registry structure, read here.
Privilege Escalation:
Bypass User Account Control (UAC) (T1548.002): MedusaLocker leverages a known UAC bypass technique involving CMSTP.exe
(Microsoft Connection Manager Profile Installer) and a malicious INF file to gain elevated privileges without user interaction. Read here to know more about privilege escalation attack.
Defense Evasion:
Impair Defenses (T1562): MedusaLocker attempts to disable security products by terminating processes and services associated with antivirus and other security software.
Impair Defenses: Safe Mode Boot (T1562.009): A key characteristic of MedusaLocker is its ability to restart the infected machine in safe mode before encryption. This bypasses many endpoint security solutions that might not be active in safe mode.
Masquerading (T1036): The copy in %AppData%\Roaming
as either svhost.exe
or svchostt.exe
.
Credential Access:
Brute Force (T1110): Brute-forcing passwords to gain initial access through RDP. To know more about what is brute force, read here.
Discovery:
File and Directory Discovery (T1083): MedusaLocker scans for files to encrypt, but it excludes specific system folders (like %User Profile%\AppData
, \ProgramData
, \Program Files
, \Windows
) to avoid rendering the system completely unusable and preventing ransom payment.
Network Share Discovery (T1135): The ransomware scans for network shares to propagate to other systems.
Query Registry (T1012): The ransomware attempts to query the registry.
Lateral Movement:
Remote Services (T1021): MedusaLocker spreads laterally through the network using RDP, PsExec, and SMB by modifying the EnableLinkedConnections
registry key and conducting ping sweeps to identify active hosts.
Command and Control:
Ingress Tool Transfer (T1105): The ransomware may use certutil.exe
to download additional tools or updates from a command-and-control (C2) server.
Impact:
Data Encrypted for Impact (T1486): MedusaLocker uses a combination of AES-256 (for symmetric file encryption) and RSA-2048 (for encrypting the AES key). This hybrid approach is designed to be efficient and secure, making brute-force decryption impractical. Encrypted files are appended with a specific extension (this extension can vary).
Inhibit System Recovery (T1490): A critical aspect of MedusaLocker's impact is its attempt to prevent system recovery. It executes commands to delete shadow copies, disable automatic startup repair, and disable Windows Error Recovery. Examples of these commands include:
vssadmin delete shadows /all /quiet
bcdedit /set {default} bootstatuspolicy ignoreallfailures
bcdedit /set {default} recoveryenabled no
wbadmin delete catalog -quiet
Service Stop (T1489): To facilitate file encryption, the ransomware kills processes of security, accounting, and forensic software.
MedusaLocker has been observed targeting organizations across a wide range of industries, demonstrating an opportunistic approach rather than a strict focus on a particular sector. However, some industries have been disproportionately affected:
Healthcare: Healthcare organizations have been frequent targets, particularly during the COVID-19 pandemic. This is likely due to the critical nature of healthcare services and the potential for significant disruption, increasing the pressure to pay the ransom. Read about healthcare data breaches here.
Education: Educational institutions have also faced frequent attacks, many times due to the lower security.
While MedusaLocker has a global reach, many reported incidents have occurred in:
North America
Europe
Several notable attack campaigns have been attributed to MedusaLocker:
Healthcare Sector Attacks (2020-2021): During the height of the COVID-19 pandemic, MedusaLocker attacks on hospitals and healthcare providers caused significant disruptions to patient care and operations.
RDP Exploitation Campaigns (Ongoing): MedusaLocker continues to leverage vulnerable RDP configurations as a primary attack vector. This highlights the ongoing need for organizations to secure their remote access infrastructure.
Defending against MedusaLocker requires a multi-layered approach, combining proactive prevention measures with robust detection and response capabilities.
Remote Desktop Protocol (RDP) Security:
Strong Passwords and Multi-Factor Authentication (MFA): Enforce strong, unique passwords for all RDP accounts and require MFA for all remote access. This is a critical defense against brute-force attacks.
Limit RDP Access: Restrict RDP access to only authorized users and IP addresses. Use a VPN or firewall rules to limit exposure.
Disable RDP if Not Needed: If RDP is not essential, disable it completely.
Phishing Prevention:
Security Awareness Training: Regularly train employees to recognize and report phishing emails. This should include training on identifying malicious attachments and suspicious links.
Email Security Gateways: Implement email security gateways that can scan for and block malicious attachments and links.
Disable hyperlinks: Disable hyperlinks in emails.
Patch Management:
Regularly Patch Systems: Promptly apply security updates for operating systems, software (especially RDP services), and firmware. This closes known vulnerabilities that MedusaLocker might exploit. Read more on patch management strategy here.
Backup and Recovery:
Regular Backups: Implement a robust backup strategy that includes regular, automated backups of critical data.
Offline Backups: Store backups offline, either on physically separate media or in a cloud-based service that is isolated from the main network. This prevents the ransomware from encrypting backups.
Test Backups: Regularly test the backup and recovery process to ensure it works as expected.
Endpoint Detection and Response (EDR):
Deploy EDR Solutions: Use an EDR solution that can detect and respond to malicious activity on endpoints, including PowerShell script execution, process injection, and attempts to disable security software. EDR solutions can often detect and block MedusaLocker's behavior even if the specific malware signature is unknown.
Network Segmentation:
Isolate Critical Systems: Segment the network to limit the lateral movement of ransomware. This can prevent a single infection from spreading to the entire organization.
Least Privilege Principle:
Restrict User Permissions: Grant users only the minimum necessary permissions to perform their job duties. This limits the potential damage from a compromised account.
Monitor for Indicators of Compromise (IOCs):
Network Traffic Monitoring: Monitor network traffic for connections to known malicious IP addresses and domains.
File System Monitoring: Monitor for the creation of files with the MedusaLocker file extension and the ransom note.
Disable Unused Ports: Disable unused ports.
Cybersecurity Awareness Training: Conduct cybersecurity awareness training for all employees, partners, contractors, etc.
MedusaLocker remains a significant and evolving ransomware threat. Its RaaS model, combined with its use of effective TTPs like RDP exploitation, PowerShell scripting, and safe mode reboot, makes it a formidable adversary. Organizations must adopt a proactive, multi-layered security approach that emphasizes prevention, detection, and response. By understanding MedusaLocker's tactics and implementing robust defenses, organizations can significantly reduce their risk of falling victim to this dangerous ransomware. Continuous monitoring, threat intelligence gathering, and adaptation to the evolving threat landscape are essential for maintaining a strong security posture against MedusaLocker and other
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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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