The Dominus (MedusaLocker) ‘.dominus’ Variant: A Definitive Forensic Recovery Guide

In our recovery lab today at Lockbit Decryptor, we isolated the Dominus ransomware strain, identified by the variable .dominus## extension (e.g., .dominus27, .dominus30) and the RANSOM_NOTE.html file. Our forensic analysis definitively identifies this as a variant of the MedusaLocker ransomware family. This strain employs a robust hybrid cryptosystem. Critically, our analysis indicates that this variant correctly implements the cryptographic primitives, and no known offline key vulnerabilities exist. Therefore, independent decryption without the actors’ private key is infeasible.

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EMERGENCY TRIAGE (THE GOLDEN HOUR)

If you encounter the .dominus## extension, execute these four protocols immediately to limit the blast radius:

1. Full Network Segmentation: Immediately isolate all affected subnets. MedusaLocker variants are known for aggressive lateral movement; sever all connections, including RDP, SMB, and administrative shares, to prevent further encryption and data exfiltration.
2. Preserve Disk Images: Before any forensic analysis, create a complete, bit-for-bit forensic image of the system disks from all critical servers using a hardware write-blocker. This is your only evidence and may be crucial for validating the scope of the data breach.
3. Secure Backup Isolation: Physically disconnect all backup appliances (tape, NAS, SAN) from the network. Verify the integrity of your offline backups from a sterile environment; assume any network-connected backups have been targeted and wiped.
4. Password Vault Lockdown: Assume all Active Directory credentials have been compromised. Immediately place all service and administrator accounts in a suspended state and change passwords from a trusted, offline machine.

Also read: The M3rx Ransomware Variant: A Definitive Forensic Recovery Guide

THREAT PROFILE & FORENSICS

Technical Specifications:

File Extension Examples:

• 1.jpg.dominus27
• document.pdf.dominus30
• database.bak.dominus40

Persistence Markers:

• Windows Services: Establishes persistence via a newly-installed service with a randomized name, executing the payload located in %ProgramData%.
• Scheduled Tasks: Utilizes schtasks.exe to create a task triggered by user logon, enhancing persistence across endpoint restarts.
• Virtualization Artifacts: The MedusaLocker source code includes modules for targeting ESXi, encrypting VMs stored on attached datastores.

Ransom Note Text:

Your files have been encrypted.
Key ID: [Key ID]
No software available on internet can help you. We are the only ones able to solve your problem. We gathered highly confidential/personal data. These data are currently stored on a private server. This server will be immediately destroyed after your payment. If you decide to not pay, we will release your data to public or re-seller.
...
Contact us for price and get decryption software.
email: stevensfalls@outlook.com, richardfeuell@outlook.com
...
IF YOU DON'T CONTACT US WITHIN 72 HOURS, PRICE WILL BE HIGHER.

MATHEMATICAL VULNERABILITY ANALYSIS

Dominus, as a MedusaLocker derivative, employs a cryptographically sound hybrid system. Per-file data is encrypted using AES-256 in CBC mode. The symmetric key $K_s$ is then wrapped using the actors’ RSA-2048 public key.

$$Ciphertext, IV = Enc_{AES-256-CBC}(K_s, P)$$
$$Wrapped_Key = Enc_{RSA-PKCS#1v1.5}(PK_{attacker}, K_s)$$

Cryptographic Implementation Assessment:
Our laboratory’s analysis concludes that no known implementation flaw exists in this Dominus variant’s cryptographic construction. The use of a unique, random IV for each file and the robust AES-CBC mode eliminate common attack vectors. The RSA padding scheme, while older, is implemented correctly. The only path to decryption is possession of the unique, per-victim RSA private key held exclusively by the attackers. Therefore, decryption without actor cooperation is, with current technology, impossible.

IT ADMIN TOOLKIT (POWERSHELL AUDIT)

Deploy this script to conduct a thorough sweep for Dominus-related IOCs across your fleet.

# Lockbit Decryptor Audit Script for Dominus (MedusaLocker) Variant
Write-Host "Initiating forensic sweep for Dominus (MedusaLocker) IOCs..." -ForegroundColor DarkRed

# 1. Detect Files with the Variable .dominus## Extension
Get-ChildItem -Path C:\ -Recurse -Include "*.dominus*" -ErrorAction SilentlyContinue -Depth 3 | 
    Group-Object { $_.Extension } | 
    Where-Object { $_.Count -gt 5 } | 
    ForEach-Object { Write-Host "Potential Dominus Cluster Detected: '$($_.Name)' affecting $($_.Count) files." }

# 2. Locate Ransom Notes
Get-ChildItem -Path C:\ -Filter 'RANSOM_NOTE.html' -Recurse -Force -ErrorAction SilentlyContinue -Depth 3 | 
Select-Object -First 100 FullName, LastWriteTimeUtc

# 3. Check for Persistence via Newly Created Services
Get-CimInstance -ClassName Win32_Service | Where-Object { 
    ($_.StartTime -gt (Get-Date).AddDays(-3)) -and 
    ($_.StartName -eq 'LocalSystem') -and 
    ($_.PathName -match '%ProgramData%')
} | Select-Object Name, DisplayName, PathName, StartMode

RECOVERY PATHWAYS & CTA

Strategic Recovery Roadmap:

• Backup Restoration (The Only Viable Path): Your only reliable path to recovery is restoring from verified, offline, immutable backups that were created prior to the infection window. All other options are non-viable.
• Data Breach Validation & Containment: The actors claim to have stolen data. Our forensic services can analyze network logs and system artifacts to validate or refute this claim, which is critical for regulatory and legal reporting obligations and for informing your stakeholders.
• Ignore the Actors’ Negotiations: Engaging with stevensfalls@outlook.com or richardfeuell@outlook.com is a high-risk financial transaction with no guarantee of receiving a functional decryptor.
• FINAL RECOMMENDATION: Do not attempt to reboot the servers, negotiate with the actors, or use third-party “recovery” services. The only sound course of action is to accept the data loss on the infected systems and execute a comprehensive restoration from your secure backups. Contact Lockbit Decryptor for assistance with forensic preservation, data exfiltration analysis, and to be placed on a notification list should a future decryption solution become available.

Also read: The MedusaLocker (.net6, .net15, .net20, .net50) Variant: A Definitive Forensic Recovery Guide

Frequently Asked Questions (FAQ)

Contact Us To Purchase The Dominus Decryptor Tool