Understanding Medusa Ransomware: Tactics, Threats, and Defenses

The recent joint cybersecurity advisory on Medusa ransomware shines a harsh light on an evolving threat that continues to keep network defenders on their toes. This advisory—released under the #StopRansomware banner by the FBI, CISA, and the MS-ISAC—provides a detailed breakdown of the tactics, techniques, and procedures (TTPs) employed by Medusa actors. As ransomware attacks surge globally, this report is an essential read for Windows administrators, IT professionals, and cybersecurity enthusiasts dedicated to protecting critical infrastructure.

A Quick Rundown on Medusa Ransomware​

Medusa ransomware first emerged in June 2021 as a ransomware-as-a-service (RaaS) model. Originally managed by a tight-knit group of cybercriminals, the ransomware has shifted to an affiliate model. However, its core operations—such as ransom negotiations—remain under centralized control, a combination that makes tracking and countering the threat especially challenging.
The advisory, which reflects insights gathered as recently as February 2025, underscores that Medusa has impacted over 300 victims across sectors like healthcare, education, legal, insurance, technology, and manufacturing. In an era when defensive measures must continually evolve to match offensive ingenuity, organizations are urged to review and implement the mitigation recommendations outlined by federal agencies.

Breaking Down the Attack​

Initial Access: How It All Begins​

Medusa’s entry into a victim’s network is often initiated through the help of initial access brokers (IABs).

• Recruitment in Cybercriminal Forums: Medusa developers offer payments ranging from $100 to $1 million USD to brokers who can provide initial network footholds.
• Phishing Campaigns: The primary mode for credential theft, phishing remains a favored tool in the Medusa playbook.
• Software Vulnerabilities: Exploiting unpatched vulnerabilities is a key tactic. Notable examples include:
  • CVE-2024-1709: An exploitation of a ScreenConnect vulnerability.
  • CVE-2023-48788: A Fortinet EMS SQL injection vulnerability, showcasing the attackers' flexibility in leveraging existing software loopholes.

In this phase, the adversaries prioritize stealth. Recruitment of IABs allows them to focus on covert initial access, using common techniques while paying a premium for exclusivity.

Discovery: Mapping the Victim’s Environment​

Once inside a network, Medusa actors shift their strategies to mapping and reconnaissance. Their approach is rooted in using legitimate tools to avoid detection.

• Living Off the Land Techniques (LOTL): The threat actors rely on tools like Advanced IP Scanner and SoftPerfect Network Scanner for enumeration.
• Commonly Scanned Ports: Attackers routinely scan ports associated with network services:
  • FTP (21), SSH (22), Telnet (23)
  • HTTP (80), SFTP (115), HTTPS (443)
  • SQL databases (1433, 3306), Firebird (3050), web proxies (3128)
  • RDP (3389)

By using everyday tools for reconnaissance, these criminals blend in with legitimate network traffic, making detection all the more challenging.

Defense Evasion: Staying in the Shadows​

Medusa actors prove to be quite sophisticated in avoiding detection throughout the compromise. Some notable techniques include:

• Obfuscated PowerShell Usage: Attackers often use PowerShell scripts with base64 encryption to conceal malicious commands. For instance:
  powershell -exec bypass -enc <base64 encrypted command string>
  This command is a familiar trick in the cybercriminal handbook, designed to evade traditional detection methods and mask true intentions.
• Slicing and Dicing Commands: In another clever variation, components of the command string are divided and obfuscated through concatenation and variable references. Such techniques make static analysis and detection significantly harder.
• Covering Their Tracks: Deleting PowerShell history (via command modifications) is another method employed to eliminate forensic evidence, complementing techniques to disable or delete EDR tools.

The sophistication in these evasion tactics reflects an ongoing arms race between threat actors and defenders. IT teams are advised to closely monitor system logs, especially those related to PowerShell and Windows Command Prompt activity, to catch subtle anomalies.

Lateral Movement and Execution: Spreading the Infection​

After gaining initial access and mapping the target network, Medusa actors move laterally to compromise additional systems.

• Remote Access Tools: A variety of legitimate remote access software are used, including:
  • AnyDesk, Atera, ConnectWise, eHorus, N-able, PDQ Deploy, PDQ Inventory, SimpleHelp, Splashtop.
  These applications, often already present within the target environment, minimize suspicion.
• Use of RDP and PsExec: The lateral movement often involves the use of RDP (Remote Desktop Protocol) and tools like PsExec:
  • Batch Scripts (openrdp.bat): These scripts facilitate the opening of RDP ports by modifying the firewall settings (e.g., creating inbound rules on TCP port 3389 and enabling WMI connectivity).
  • Registry Modifications: Commands to alter registry settings (such as allowing Remote Desktop connections) are executed to ensure persistent access.

A critical takeaway here is that the attackers use legitimate tools in combination with administrative commands to both fortify their presence and expand their reach within the network.

Exfiltration and Encryption: The Crux of the Attack​

In the heart of the Medusa operation lies the dual-purpose strategy of exfiltration and encryption.

• Data Exfiltration: Tools like Rclone are deployed to siphon data back to the attackers’ Command and Control (C2) servers. This step is essential for the subsequent extortion process.
• Encryption with Double Extortion Model: After data exfiltration, Medusa encrypts files with AES-256 using a proprietary encryptor, typically named “gaze.exe.” Key elements include:
  • Disabling Security Services: The ransomware often terminates services including Windows Defender, diminishing the victim's defense.
  • Shadow Copy Deletion: By removing shadow copies, the malware ensures that recovery options are limited.
  • File Extension Marking: Encrypted files receive the ".medusa" extension, a clear indicator of the attack.

The Price of Non-Compliance: Extortion Schemes Unveiled​

Unlike traditional ransomware which solely encrypts data and demands ransom for decryption, Medusa incorporates a double extortion strategy. Here's how it works:

• Dual Threat: Not only must victims pay to recover encrypted data, but the attackers also threaten to expose sensitive, exfiltrated information on their .onion data leak site.
• Negotiation Channels: Victims are instructed to contact attackers via Tor-based live chats or encrypted messaging platforms like Tox. Failure to respond triggers direct outreach via phone or email.
• Increased Pressure with Countdown Timers: The ransomware’s interface includes a countdown to data release. Victims can even pay an extra fee (e.g., $10,000 USD) to extend the timer. Disturbingly, there are reports of triple extortion—where even after an initial ransom is paid, further demands are issued, claiming that the "true decryptor" was withheld due to internal theft of the funds.

This multi-layered extortion strategy not only heightens the risk but also amplifies the financial and reputational damage inflicted upon the victim.

Technical Indicators: IOCs and Email Addresses​

To assist organizations in quickly identifying and mitigating attacks, the advisory includes thorough lists of Indicators of Compromise (IOCs). Two notable tables are:

• Table of Malicious Files: This includes filenames and their associated MD5 hashes—for instance:
  • openrdp.bat: With the hash 44370f5c977e415981febf7dbb87a85c. This script is critical as it opens the gateway for RDP connections.
  • pu.exe: A reverse shell component used in lateral movement.
• Table of Medusa Email Addresses: These addresses (such as key.medusa.serviceteam@protonmail.com and medusa.support@onionmail.org) are central to ransom negotiations. Notably, these email addresses are reserved exclusively for extortion communications, not for phishing efforts.

These detailed technical indicators provide a roadmap for defenders to monitor network traffic and identify malicious artifacts on compromised systems.

Mapping to the MITRE ATT&CK Framework​

The advisory leverages the MITRE ATT&CK® Matrix for Enterprise (version 16) to correlate the threat actor’s behavior with known adversary tactics. Key mappings include:

• Initial Access (TA0001) and Phishing (T1566): Illustrating the methods for network infiltration.
• Defense Evasion (TA0005): Highlighting techniques like command obfuscation and deletion of logs to foil detection.
• Lateral Movement (TA0008) and Exfiltration (TA0010): Outlining methods such as leveraging remote execution tools and transferring data covertly.
• Impact (T1486): Focusing on the encryption of data and shutting down backup systems.

The use of the MITRE framework serves as a valuable cross-reference for security teams looking to map their existing defenses against the comprehensive list of tactics presented in this advisory.

Strategic Mitigations: What You Can Do​

For Windows administrators and network defenders eager to bolster their security posture against evolving ransomware threats such as Medusa, here are some key recommendations:

• Regular Patching: Ensure that all systems are promptly updated to mitigate vulnerabilities like CVE-2024-1709 and CVE-2023-48788.
• Enhanced Monitoring: Keep a close watch on PowerShell activities, remote desktop sessions, and the use of tools typically associated with administrative tasks (e.g., PsExec).
• Network Segmentation: Restrict lateral movement by segmenting critical infrastructure and limiting access to sensitive ports.
• Incident Response Preparedness: Establish and routinely update an incident response plan that includes steps to counter ransomware-specific tactics, such as disabling remote access or isolating affected machines.
• User Education: Regularly train employees on against phishing and social engineering tactics—a common initial entry point for many ransomware attacks.

Implementing these mitigations not only minimizes the impact of an attack but also strengthens your overall security framework against future ransomware incursions.

Wrapping It All Up​

The Medusa ransomware advisory is a stark reminder of how dynamic and multifaceted modern ransomware threats have become. With a blend of traditional ransomware tactics and innovative extortion methods, Medusa forces IT teams to be more vigilant than ever. The detailed technical insights provided in the advisory—ranging from the exploitation of vulnerabilities and illicit use of legitimate tools to rapid lateral movement and devious extortion schemes—offer a critical playbook for defense.
For Windows professionals focused on maintaining robust security measures, this advisory reinforces the necessity of a holistic defense strategy. Not only should organizations aim to patch vulnerabilities and monitor network anomalies, but they must also be prepared to adapt rapidly to emerging threats. As ransomware continues to evolve, so too must the methods and techniques used to counter it.
In a world where one misstep can lead to an all-out cyberattack, defenders must stay informed and always be one step ahead. This comprehensive advisory on Medusa is not just a technical manual—it is a call to action for robust cybersecurity practices in every organization. Stay alert, stay secure, and remember: in the evolving landscape of cyber threats, preparedness is the best defense.
Whether you’re managing a Windows enterprise environment or simply keen on current cybersecurity trends, integrating the lessons from this advisory into your security strategy is vital for safeguarding your digital assets.

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Source: CISA #StopRansomware: Medusa Ransomware | CISA