Storm-1175 and Medusa Ransomware: Defending Against Rapid Exploitation of New Vulnerabilities

---
title: Medusa Ransomware - VSS Shadow Copy Deletion
id: 92e1d2a3-4b5c-6d7e-8f9a-1b2c3d4e5f6a
status: experimental
description: Detects the deletion of Volume Shadow Copies which is a common step for Medusa and other ransomware to prevent recovery.
references:
 - https://attack.mitre.org/techniques/T1490/
author: Security Arsenal
date: 2025/04/16
tags:
 - attack.impact
 - attack.t1490
logsource:
 category: process_creation
 product: windows
detection:
 selection:
   Image|endswith: '\vssadmin.exe'
   CommandLine|contains: 'delete shadows'
 condition: selection
falsepositives:
 - System administrators performing maintenance (rare)
level: high
---
title: Medusa Ransomware - Note File Creation
id: 1a2b3c4d-5e6f-7g8h-9i0j-1k2l3m4n5o6p
status: experimental
description: Detects the creation of README.txt files which Medusa uses as ransom notes. Highly indicative when found in user directories or network shares.
references:
 - Internal Threat Research
author: Security Arsenal
date: 2025/04/16
tags:
 - attack.impact
 - attack.t1486
logsource:
 category: file_create
 product: windows
detection:
 selection:
   TargetFilename|contains: '\README'
   TargetFilename|endswith: '.txt'
 condition: selection
falsepositives:
 - Legitimate software installation or documentation creation
level: medium
---
title: Medusa Ransomware - Suspicious Process Execution
id: 7g8h9i0j-1k2l-3m4n-5o6p-7q8r9s0t1u2v
status: experimental
description: Detects execution of typical Medusa ransomware process names or binaries spawned from unusual locations.
references:
 - https://www.mandiant.com/resources/blog/medusa-ransomware
author: Security Arsenal
date: 2025/04/16
tags:
 - attack.execution
 - attack.t1059
logsource:
 category: process_creation
 product: windows
detection:
 selection:
   Image|endswith:
     - '\medusa.exe'
     - '\rundll32.exe' # Often used for DLL side-loading
   CommandLine|contains:
     - '-encrypt'
     - '-lock'
 condition: selection
falsepositives:
 - None expected for 'medusa.exe'
level: critical

// Hunt for Medusa Ransomware Indicators
// 1. VSS Deletion
let VSSDeletion =
DeviceProcessEvents
| where Timestamp > ago(7d)
| where FileName =~ "vssadmin.exe"
| where ProcessCommandLine contains "delete" and ProcessCommandLine contains "shadows"
| project Timestamp, DeviceName, AccountName, ProcessCommandLine, FolderPath;
// 2. Ransom Note Creation
let RansomNote =
DeviceFileEvents
| where Timestamp > ago(7d)
| where FileName startswith "README" and FileName endswith ".txt"
| project Timestamp, DeviceName, InitiatingProcessAccountName, FileName, FolderPath;
// 3. High volume file changes (potential encryption)
let FileEncryption =
DeviceFileEvents
| where Timestamp > ago(1h)
| where ActionType == "FileCreated"
| where FileName endswith ".medusa" // Known extension used sometimes
| summarize count() by DeviceName, bin(Timestamp, 5m)
| where count_ > 50;
// Union results
union VSSDeletion, RansomNote

-- Hunt for Medusa Ransomware Notes and VSS Deletion Artifacts
SELECT 
  FullPath, 
  Size, 
  Mtime, 
  Mode.String as Mode,
  Data.Data as ContentPreview
FROM glob(globs="/*RE*.txt", root="/")
WHERE Mtime > now() - 7d

-- Check for vssadmin execution in recent process logs
SELECT Pid, Name, CommandLine, Exe
FROM pslist()
WHERE Name =~ "vssadmin.exe" 
   AND CommandLine =~ "delete"
   AND Exe =~ "vssadmin.exe"

# Medusa / Storm-1175 Response Script
# Run as Administrator on potentially affected endpoints

Write-Host "[+] Starting Medusa Ransomware Hunt and Hardening..." -ForegroundColor Cyan

# 1. Scan for Ransom Notes in User Profiles
Write-Host "[!] Scanning for README*.txt ransom notes..." -ForegroundColor Yellow
$notes = Get-ChildItem -Path C:\Users\ -Recurse -Filter "README*.txt" -ErrorAction SilentlyContinue
if ($notes) {
    foreach ($note in $notes) {
        Write-Host "[!!] FOUND RANSOM NOTE: $($note.FullName)" -ForegroundColor Red
        # Log to event log for SIEM correlation
        Write-EventLog -LogName Application -Source "SecurityArsenal" -EntryType Error -EventId 9999 -Message "Medusa Ransom Note Found: $($note.FullName)"
    }
} else {
    Write-Host "[+] No ransom notes found." -ForegroundColor Green
}

# 2. Verify VSS Service Status (Often disabled by Medusa)
Write-Host "[!] Checking Volume Shadow Copy Service..." -ForegroundColor Yellow
$vssService = Get-Service -Name VSS -ErrorAction SilentlyContinue
if ($vssService.Status -ne "Running") {
    Write-Host "[!!] WARNING: VSS Service is not running. Attempting to start..." -ForegroundColor Red
    try {
        Start-Service -Name VSS -ErrorAction Stop
        Write-Host "[+] VSS Service started successfully." -ForegroundColor Green
    } catch {
        Write-Host "[!!] Failed to start VSS Service." -ForegroundColor Red
    }
} else {
    Write-Host "[+] VSS Service is running." -ForegroundColor Green
}

# 3. Network Hardening - Block RDP from Internet (Firewall Rule Check)
Write-Host "[!] Checking for open RDP rules..." -ForegroundColor Yellow
$rdpRules = Get-NetFirewallRule | Where-Object { $_.Enabled -eq $true -and $_.Direction -eq "Inbound" -and ($_.DisplayName -like "*Remote Desktop*" -or $_.DisplayGroup -like "*Remote Desktop*") }
if ($rdpRules) {
    Write-Host "[!!] Active RDP Firewall Rules found. Review scope:" -ForegroundColor Red
    $rdpRules | Select-Object DisplayName, Profile, Direction, Action | Format-Table
} else {
    Write-Host "[+] No standard RDP rules found or enabled." -ForegroundColor Green
}

Write-Host "[+] Script complete. Review logs for findings." -ForegroundColor Cyan