Medusa Ransomware Removal Guide

Signs of Infection

A system infected with Medusa ransomware will display several distinct indicators. Immediate signs include widespread file encryption with the .medusa extension appended to original filenames. A ransom note named !!!READ_ME_MEDUSA!!!.txt or similar will appear in affected directories, containing payment instructions and a unique victim ID.

File system artifacts include the creation of malicious executables in temporary directories (%TEMP%, %APPDATA%, %LOCALAPPDATA%) with random alphanumeric names. Look for new, suspicious processes in memory, often with names mimicking legitimate system processes but with slight misspellings or random characters. Medusa may attempt to delete Volume Shadow Copies using commands like vssadmin delete shadows /all /quiet and disable Windows recovery features.

Network signs involve outbound connections to command-and-control (C2) servers over HTTPS or specific ports. These communications often occur shortly before encryption begins. The malware may also attempt to spread via Server Message Block (SMB) if credentials are compromised. Unusual spikes in network traffic to unfamiliar external IP addresses or domains are a critical warning sign.

Immediate Containment Steps

Within the first 15 minutes of detection, take these steps to prevent further damage.

1. Isolate the Affected System(s): Immediately disconnect the infected machine from the network-both wired and wireless. If the infection is suspected on multiple systems, consider isolating the entire network segment.
2. Identify the Scope: Determine if the infection is isolated to a single endpoint or has spread to network shares, servers, or other connected systems. Check critical servers and backup systems first.
3. Terminate Malicious Processes: Using a dedicated endpoint security tool or command-line utilities, identify and kill any processes associated with Medusa. Look for processes with high CPU or disk activity related to file encryption.
4. Disable Compromised Accounts: If there is any indication of lateral movement, immediately rotate credentials for any potentially compromised local or domain administrator accounts. Enforce strong, unique passwords.
5. Preserve Evidence: Before any removal or cleanup, take forensic images of memory and disk from a sample of affected systems if possible. Secure copies of the ransom note and encrypted files for later analysis. Do not delete or modify files yet.

Manual Removal Process

Warning: Manual removal is complex and carries risk. It is recommended only if professional tools are unavailable. Have a known-clean backup of the system ready before proceeding.

1. Enter Safe Mode: Restart the infected computer and boot into Safe Mode with Networking to prevent Medusa from loading its components.
2. Terminate Malware Processes:
   • Open the Task Manager and go to the Details tab.
   • Look for suspicious processes with random names or those consuming significant resources. Common locations include %TEMP%\random.exe or %APPDATA%\Microsoft\random.exe.
   • Right-click and select “End task” for each identified malicious process.
3. Delete Malicious Files:
   • Open File Explorer and enable viewing of hidden files and protected operating system files.
   • Navigate to and delete files from these directories:
     • %TEMP%
     • %APPDATA%
     • %LOCALAPPDATA%
     • C:\Windows\Temp
   • Search for and delete any files created around the time of infection with random names and .exe or .dll extensions. Do not delete the encrypted user files or the ransom note at this stage if recovery is a possibility.
4. Remove Persistence Mechanisms:
   • Open the Registry Editor (regedit).
   • Navigate to and carefully check these keys for suspicious entries pointing to the malware file paths:
     • HKCU\Software\Microsoft\Windows\CurrentVersion\Run
     • HKLM\Software\Microsoft\Windows\CurrentVersion\Run
     • HKLM\Software\Microsoft\Windows\CurrentVersion\RunOnce
   • Delete any keys or values that reference the malicious files identified in Step 3.
5. Clean Scheduled Tasks:
   • Open Task Scheduler.
   • Review the task library for any recently created or suspicious tasks that may be configured to run the malware. Delete any tasks linked to Medusa.

Verifying Removal

After completing the removal steps, verify the system is clean.

1. Conduct Full System Scans: Perform deep, full-system scans using a modern endpoint detection and response (EDR) tool and a dedicated anti-malware scanner. Ensure they are updated with the latest signatures.
2. Monitor System Activity: Use process monitoring tools to watch for the return of any malicious processes or the creation of files in temporary directories. Monitor for unexpected network connections.
3. Check System Logs: Review Windows Event Logs (especially Security, System, and Application logs) for any residual malicious activity, failed attempts to create persistence, or unexpected service installations around the time of your cleanup.
4. Validate Network Traffic: Use a network monitoring tool or SIEM platform to confirm no further outbound communication to known Medusa C2 servers (refer to the Current Medusa IOCs for specific indicators).
5. Test System Functionality: Ensure critical operating system functions work, and no legitimate services were disabled by the malware.

Post-Removal Security Hardening

To prevent reinfection and strengthen defenses against similar threats:

1. Restore from Clean Backups: If files were encrypted, restore data from known-clean, offline backups. Verify the integrity of backups before restoration.
2. Patch and Update: Aggressively patch all operating systems, software, and firmware. Medusa often exploits known vulnerabilities for initial access.
3. Harden Endpoint Configurations:
   • Implement application allowlisting to prevent execution of unauthorized software from %TEMP% and %APPDATA%.
   • Disable unnecessary macros in office documents and restrict script execution (e.g., PowerShell Constrained Language Mode).
   • Enable controlled folder access or similar features to block unauthorized changes to files in key directories.
4. Strengthen Access Controls: Enforce the principle of least privilege. Use multi-factor authentication (MFA) for all remote access and administrative accounts. Regularly audit user and service account permissions.
5. Enhance Monitoring:
   • Deploy and tune an EDR solution across all endpoints.
   • Create specific SIEM alerts for the creation of files with the .medusa extension, commands used to delete shadow copies (vssadmin, bcdedit), and network connections to IPs/domains on the IOC list.
   • Monitor for unusual file share access patterns and lateral movement attempts.
6. Review and Test Backups: Ensure backups follow the 3-2-1 rule (three copies, two media, one offline). Regularly test backup restoration procedures.
7. Conduct User Training: Educate users on phishing tactics, safe browsing, and the importance of reporting suspicious emails or system behavior immediately.

For more information on Medusa’s behavior, see the Medusa Overview. For the latest detection metrics, check the Detection Rate page.