Medusa Ransomware: Rapid Zero-Day Weaponization and Encryption Countermeasures

---
title: Medusa Ransomware Rclone Exfiltration Pattern
id: 9e8c7d1a-2b3f-4c5e-9a0b-1c2d3e4f5a6b
status: experimental
description: Detects the use of rclone.exe for data exfiltration, a common TTP for Medusa operators. Rclone is often used to sync large volumes of data to cloud storage rapidly.
references:
 - https://attack.mitre.org/techniques/T1041/
author: Security Arsenal
date: 2025/04/10
tags:
 - attack.exfiltration
 - attack.t1041
logsource:
 category: process_creation
 product: windows
detection:
  selection:
    Image|endswith:
      - '\rclone.exe'
    CommandLine|contains:
      - 'sync'
      - 'copy'
  condition: selection
falsepositives:
 - Legitimate administrator backup tasks using rclone
level: high
---
title: Medusa Ransomware Note Creation
id: b1a2c3d4-5e6f-7a8b-9c0d-1e2f3a4b5c6d
status: experimental
description: Detects the creation of Medusa ransom notes. Medusa typically drops a file named "README.txt" or variations containing "MEDUSA" in the root directories.
references:
 - https://attack.mitre.org/techniques/T1485/
author: Security Arsenal
date: 2025/04/10
tags:
 - attack.impact
 - attack.t1485
logsource:
 category: file_create
 product: windows
detection:
  selection:
    TargetFilename|contains:
      - '\README_MEDUSA'
      - '!!!README_MEDUSA!!!'
      - 'RECOVER-FILES'
    TargetFilename|endswith:
      - '.txt'
      - '.hta'
  condition: selection
falsepositives:
 - Rare (User creating readme files with specific ransomware keywords)
level: critical
---
title: Potential Medusa Anti-Forensic Deletion
id: c3d4e5f6-7a8b-9c0d-1e2f-3a4b5c6d7e8f
status: experimental
description: Detects commands used to delete VSS shadow copies and clear logs, often executed by Medusa prior to encryption.
references:
 - https://attack.mitre.org/techniques/T1490/
author: Security Arsenal
date: 2025/04/10
tags:
 - attack.defense_evasion
 - attack.t1490
logsource:
 category: process_creation
 product: windows
detection:
  selection:
    Image|endswith:
      - '\vssadmin.exe'
      - '\wbadmin.exe'
      - '\powershell.exe'
    CommandLine|contains:
      - 'delete shadows'
      - 'delete catalog'
      - 'Clear-EventLog'
  condition: selection
falsepositives:
 - System administrator maintenance
level: medium

let SuspiciousProcesses = dynamic(["cmd.exe", "powershell.exe", "pwsh.exe", "wscript.exe", "cscript.exe"]);
// Look for high volume egress from a single host shortly after process execution
DeviceNetworkEvents
| where ActionType == "ConnectionSuccess" and RemotePort in (443, 80)
| summarize TotalBytesSent = sum(SentBytes), CountOfConnections = count() by DeviceName, bin(Timestamp, 5m)
| where TotalBytesSent > 50000000 // Threshold: 50MB in 5 minutes
| join kind=inner (
    DeviceProcessEvents
    | where FileName in~ SuspiciousProcesses
    | project DeviceName, ProcessCreationTime = Timestamp, ProcessCommandLine, InitiatingProcessFileName
) on DeviceName
| where Timestamp between (ProcessCreationTime - 1h) and (ProcessCreationTime + 1h)
| project DeviceName, ProcessCreationTime, ProcessCommandLine, InitiatingProcessFileName, TotalBytesSent, Timestamp
| order by ProcessCreationTime desc

-- Hunt for Medusa Ransom Notes
SELECT FullPath, Size, Mtime, Mode
FROM glob(globs="\\\\?\\C:\\*\README*", root="/")
WHERE FullPath =~ "MEDUSA" OR FullPath =~ "RECOVER"
UNION ALL
SELECT FullPath, Size, Mtime, Mode
FROM glob(globs="\\\\?\\*\README*.txt", root="/")
WHERE FullPath =~ "MEDUSA"

# Medusa Ransomware Identification and Isolation Script
# Usage: .\Check-Medusa.ps1

Write-Host "[+] Starting Medusa Artifact Hunt..." -ForegroundColor Cyan

# 1. Check for common Medusa Ransom Note patterns
$drives = Get-PSDrive -PSProvider FileSystem | Select-Object -ExpandProperty Root
$foundNotes = @()

foreach ($drive in $drives) {
    Write-Host "[+] Scanning $drive for ransom notes..." -ForegroundColor Yellow
    $notes = Get-ChildItem -Path $drive -Filter "*README*" -Recurse -ErrorAction SilentlyContinue | 
             Where-Object { $_.Name -match "MEDUSA|RECOVER|FILES" -and $_.Extension -match "\.(txt|hta|html)" }
    if ($notes) {
        $foundNotes += $notes
    }
}

if ($foundNotes) {
    Write-Host "[!!!] CRITICAL: Medusa Ransom Notes Detected:" -ForegroundColor Red
    $foundNotes | ForEach-Object { Write-Host "    - $($_.FullName)" }
    # Recommended immediate action: Disconnect network
} else {
    Write-Host "[-] No standard Medusa notes found." -ForegroundColor Green
}

# 2. Check for Rclone execution (Indicative of exfil)
$rclonePath = "C:\Windows\Temp\rclone.exe"
if (Test-Path $rclonePath) {
    Write-Host "[!!!] WARNING: Rclone found in temp directory (Potential Exfil Tool)" -ForegroundColor Red
}

# 3. Review Security Event Logs for unusual mass file deletions (ID 4663)
Write-Host "[+] Checking Event Logs for mass file access patterns (Requires Admin)..." -ForegroundColor Yellow
# Note: Advanced Event Log parsing omitted for brevity, ensure Security Logs are forwarded to SIEM.