Incident Response Guide: Medusa Ransomware

Incident Triage Steps

Within the first 30 minutes of a suspected Medusa ransomware incident, your priority is to confirm the outbreak, assess its scope, and determine if data theft occurred. Medusa typically leaves a ransom note named !!!READ_ME_MEDUSA!!!.txt or similar in affected directories. Immediately search for this file across network shares and critical servers using a centralized logging or endpoint detection platform. Identify the initial compromised system by reviewing authentication logs for unusual remote desktop protocol (RDP) or virtual private network (VPN) connections, as Medusa often spreads via stolen credentials. Check for the creation of batch files (.bat) or PowerShell scripts in temporary directories, which Medusa uses for lateral movement. To determine if data exfiltration occurred-a common tactic before encryption-examine outbound network traffic logs for large, unusual transfers to unfamiliar external IP addresses or domains. Medusa operators may use cloud storage services or their own command and control servers for this. Quickly compile a list of affected systems by scanning for files with the .medusa extension or other new extensions appended by the ransomware. Isolate these systems logically from the network if possible without alerting the attacker, but prioritize evidence collection first.

Evidence Collection

Before initiating containment or eradication, preserve the following evidence for forensic analysis and potential legal proceedings. On a sample of affected systems-especially the initial entry point-capture a full memory dump using a trusted forensic tool. This may reveal encryption keys, command and control IP addresses, and malware binaries resident in memory. Export a detailed process list, noting any processes with suspicious names or high CPU usage associated with file encryption. Collect Medusa-specific artifacts: the ransom note files, any batch or script files in C:\Windows\Temp\ or user AppData folders, and registry modifications at HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Run or similar auto-start locations. Preserve logs from the host firewall, Windows Event Logs (particularly Event ID 4688 for process creation and 4624/4625 for logons), and any endpoint detection platform alerts. For network evidence, ensure full packet captures from border and internal network sensors are saved, focusing on traffic to known Medusa command and control IPs or domains identified in threat intelligence feeds. Retain backup snapshots from just before the encryption began, as they may contain unencrypted data and indicators of the initial compromise.

Containment Procedures

To stop Medusa’s spread without destroying evidence, first implement network segmentation. Disable any unnecessary network shares and remote access services like RDP and Server Message Block (SMB) on unaffected systems. Use network access control or firewall rules to isolate compromised subnets, blocking all traffic except that required for investigation. Reset credentials comprehensively: change passwords for all domain admin accounts, local admin accounts on critical servers, and any service accounts that may have been exposed. Focus on accounts that showed anomalous logins in the triage phase. Block Medusa’s command and control communication by updating firewall and proxy blocklists with indicators from your evidence collection, such as specific IP addresses and domains associated with Medusa’s infrastructure. If Medusa is using a living-off-the-land binary like wmic.exe or powershell.exe for lateral movement, consider temporarily restricting their execution via application whitelisting policies on unaffected systems, but ensure this does not hinder business-critical operations.

Eradication and Recovery

Complete eradication requires removing Medusa from all affected systems. Follow the detailed, step-by-step procedures in the Removal Guide for each endpoint. This typically involves killing malicious processes, deleting persisted registry keys and scheduled tasks, and removing the ransomware binary and associated scripts. Only after eradication should you begin recovery. Restore encrypted files from clean, offline backups that predate the infection. Verify the integrity of these backups by checking for malware artifacts before restoration. After restoring data, rebuild any systems that cannot be reliably cleaned, such as domain controllers or database servers, from known-good images. To verify a clean state, perform a full scan with an updated endpoint detection solution across all systems, monitor for recurrence of Medusa-related network indicators, and validate that no new files are being encrypted. Re-enable network access and services gradually, with close monitoring for any signs of re-infection.

Lessons Learned Checklist

After containment and recovery, conduct a post-incident review to improve defenses against future Medusa attacks. Answer these questions specifically:

• Initial Access: How did Medusa enter? Review VPN or RDP logs for brute-force attacks, phishing email analysis, or exploitation of unpatched vulnerabilities in public-facing services.
• Control Failures: Which controls failed? Consider multi-factor authentication (if absent for remote access), endpoint detection rules that missed malicious PowerShell execution, or inadequate network segmentation that allowed lateral movement.
• Detection Gaps: What detection gaps existed? Analyze if security monitoring missed the creation of ransom notes, large-scale file encryption events, or outbound data transfers to Medusa’s command and control servers.
• Improvements: What must be improved? Prioritize implementing multi-factor authentication on all remote access points, enhancing logging and alerting for suspicious RDP logins and mass file renames, and conducting regular backup restoration tests to ensure rapid recovery.
• Attack Chain Alignment: How did this incident align with typical Medusa tactics? Compare your findings to known behaviors documented in the Medusa Overview and update your Detection Guide accordingly.

Use this guide in conjunction with the linked resources to respond effectively and strengthen your resilience against Medusa ransomware.