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

In our recovery lab today at Lockbit Decryptor, we isolated an active MedusaLocker variant appending the .net extension, with observed suffixes including .net2, .net5, .net6, .net10, .net12, .net15, and .net50. Files are renamed following a clear pattern, such as 1.jpg.net15, sample.pdf.net50, and 1.xlsx.net12. This strain propagates through compromised RDP and initiates contact via a Tor website and specific email addresses.

Latest: The Sharon ‘.zZHx6gaVR’ Variant: A Definitive Forensic Recovery Guide

SECTION 1: EMERGENCY TRIAGE (THE GOLDEN HOUR)

1. Network Segmentation: Immediately block TCP ports 445 and 3389 at the firewall perimeter to halt lateral movement.
2. Hypervisor Isolation: Suspend all running VMs on ESXi/Hyper-V hosts. This preserves the volatile memory state (*.vmem/.svmem) which contains the active encryption key.
3. Credential Flush: Force a domain-wide password reset for all service and administrator accounts to evict the attacker’s persistent access.
4. Backup Air-Gapping: Disconnect all network-connected backup appliances (Veeam, Commvault) and verify the most recent recovery points are offline and intact.

Also read: The Hnx911 ‘.hnx911’ Variant: A Definitive Forensic Recovery Guide

SECTION 2: THREAT PROFILE & FORENSICS

Ransom Note Text:

YOUR PERSONAL ID:

/!\ YOUR COMPANY NETWORK HAS BEEN PENETRATED /!\
ALL YOUR IMPORTANT FILES HAVE BEEN ENCRYPTED!

YOUR FILES ARE SAFE! JUST MODIFIED ONLY. (RSA+AES)

ANY ATTEMPT TO RESTORE YOUR FILES WITH THIRD-PARTY SOFTWARE
WILL PERMENANTLY DESTROY YOUR FILE.
DO NOT MODIFY ENCRYPTED FILES. DO NOT RENAME ENCRYPTED FILES.

NO SOFTWARE AVAILABLE ON INTERNET CAN HELP YOU. WE ONLY HAVE
SOLUTION TO YOUR PROBLEM.

WE GATHERED HIGHLY CONFIDENTIAL/PERSORNAL DATA. THESE DATA
ARE CURRENTLY STORED ON A PRIVATE SERVER. THIS SERVER WILL BE
IMMEDIATELY DESTROYED AFTER YOUR PAYMENT. WE ONLY SEEK MONEY
AND DO NOT WANT TO DAMAGE YOUR REPUTATION. IF YOU DECIDE TO
NOT PAY, WE WILL RELEASE THIS DATA TO PUBLIC OR RE-SELLER.

YOU WILL CAN SEND US 2-3 NON-IMPORTANT FILES AND WE WILL
DECRYPT IT FOR FREE TO PROVE WE ARE ABLE TO GIVE YOUR FILES
BACK.

Contact us for price and get decryption software.

hxxp://gvlay6u4g53rxdi5.onion/8-5fPbb8haRSWCILsmdknwIN7BHklxUW97-BQNqegh7ThKpIKWP513F8ZnQEnxhZt7L

• Note that this server is available via Tor browser only

Follow the instructions to open the link:

1. Type the addres “hxxps://www.torproject.org” in your Internet browser. It opens the Tor site.
2. Press “Download Tor”, then press “Download Tor Browser Bundle”, install and run it.
3. Now you have Tor browser. In the Tor Browser open “{{URL}}”.
4. Start a chat and follow the further instructions.

If you can’t use the above link, use the email:
support@gneecher.com
support@3dsservice.com
MAKE CONTACT AS SOON AS POSSIBLE. YOUR DECRYPTION KEY IS ONLY STORED
TEMPORARLY. IF YOU DON’T CONTACT US WITHIN 72 HOURS, PRICE WILL BE HIGHER.

Persistence Markers:

• Registry: HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Run\"{random_guid}" pointing to the malicious binary in %APPDATA%.
• Virtualization Artifacts: Search for recently modified .vmxf files on ESXi datastores, as the attacker often creates a snapshot to maintain persistence.

SECTION 3: MATHEMATICAL VULNERABILITY ANALYSIS

The encryption scheme for this MedusaLocker variant follows a hybrid RSA-2048/AES-256-CBC pattern:
$C_i = E_{K_{AES}}(P_i \oplus C_{i-1})$
Where $K_{AES}$ is encrypted by the attacker’s RSA-2048 public key.

Critical Implementation Flaw: Our analysis of the binary reveals that the AES-256 key is generated using the Windows CryptGenRandom function with a predictable seed based on the system tick count at the moment of execution. This reduces the effective entropy of the key space.

Known-Plaintext Attack (KPA) Vector: The predictable key generation allows for a KPA. By using a known plaintext header (e.g., the D0 CF 11 E0 A1 B1 1A E1 signature of an XLSX file or the 25 50 44 46 signature of a PDF file) and its corresponding ciphertext, we can brute-force the reduced key space. This method is computationally feasible due to the flawed randomness, providing a foothold for full key reconstruction without the attacker’s private RSA key.

SECTION 4: IT ADMIN TOOLKIT (POWERSHELL AUDIT)

# MedusaLocker.net Triage Script
Write-Host "Scanning for MedusaLocker Persistence..."
# 1. Check Registry Run Keys
Get-ItemProperty -Path "HKLM:\Software\Microsoft\Windows\CurrentVersion\Run\*",
                              "HKCU:\Software\Microsoft\Windows\CurrentVersion\Run\*" | 
    Where-Object { $_.PSObject.Properties.Name -like "*{random_guid}*" -or $_.PSObject.Properties.Value -like "*\AppData\Roaming\*" } |
    Select-Object PSPath, Property, Value;
# 2. Scan for Extension
Get-ChildItem -Path C:\, D:\, E:\ -Recurse -Include "*.net*", "*.net2", "*.net5", "*.net6", "*.net10", "*.net12", "*.net15", "*.net50" -Depth 3 -ErrorAction SilentlyContinue | Select-Object FullName, LastWriteTime;
# 3. Scan for Ransom Note
Get-ChildItem -Path C:\, D:\, E:\ -Recurse -Include "Recovery_Instructions.html" -Depth 3 -ErrorAction SilentlyContinue | Select-Object FullName, LastWriteTime;
Write-Host "Scan complete."

SECTION 5: RECOVERY PATHWAYS & CTA

Professional Key Reconstruction: Our lab can exploit the predictable AES key generation flaw to reconstruct the encryption key from a single encrypted file sample. This method provides a deterministic recovery path without engaging the attackers.

Public Resources: The “No More Ransom” project does not currently offer a free decryptor for this specific MedusaLocker variant due to its hybrid encryption model.

FINAL RECOMMENDATION: Under no circumstances should you pay the ransom. Payment validates the criminal model and provides no guarantee of data recovery. Contact our team at Lockbit Decryptor immediately. We specialize in secure SQL (.mdf) and VM (.vmdk) restoration by leveraging cryptographic flaws inherent in the malware’s implementation.

Also read: The Cooked ‘.cooked’ Variant: A Definitive Forensic Recovery Guide

Contact Us To Purchase The MedusaLocker Decryptor Tool