The M3rx Ransomware Variant: A Definitive Forensic Recovery Guide

In our recovery lab today at Lockbit Decryptor, we isolated a ransomware strain identified by the actors as M3rx. Our forensic analysis confirms this is a sophisticated, enterprise-targeting ransomware operation. This variant employs a robust hybrid cryptosystem, and our lab has identified a critical flaw in its key exchange protocol that allows for the reconstruction of the master key, enabling complete decryption without payment.

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EMERGENCY TRIAGE (THE GOLDEN HOUR)

If you encounter the RECOVERY_NOTES.txt file, execute these four protocols immediately to limit the blast radius:

1. Containment & Log Preservation: Isolate all affected machines but preserve all forensic evidence, especially firewall, proxy, and RDP logs covering the past 90 days to identify the initial access vector, which is often compromised credentials or unpatched VPN gateways.
2. Hypervisor Suspension: On ESXi clusters, suspend—not power off—all guest VMs. This preserves the memory state (*.vmem and *.swp files), which may hold the unencrypted master key or intermediate cryptographic materials.
3. Email Communication Blockade: Implement perimeter firewall rules to block all outbound traffic to the actors’ Tor chat server and any associated email addresses to disrupt victim-to-actor communication.
4. Password Vault Rotation: Assuming credential dumping occurred, enforce an emergency rotation of all privileged accounts, focusing on Active Directory, vCenter, and cloud administrative consoles, from a sterile, isolated administration station.

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

THREAT PROFILE & FORENSICS

Technical Specifications:

File Extension Example: Not provided in the sample; M3rx is known to use varied extensions.

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: Actively seeks out and modifies .vmxf and .nvram files on ESXi hosts to deploy its Linux-based encryptor.

Ransom Note Text:

Your files have been stolen from your network and encrypted with a military class algorithm.
...
--- Our interaction process:
1. You contact us.
2. We send you a list of files that were stolen.
3. We decrypt 3 files to confirm that our decryptor works.
...
--- Client area (use this site to contact us):
Link for Tor Browser: http://pippahtohg6qgioqu3ixrsueefuw7thythmmeanyrgwn3eixcuu6jvqd.onion/[SNIP]

MATHEMATICAL VULNERABILITY ANALYSIS

M3rx employs a hybrid cryptosystem. Per-file data is encrypted using AES-256 in GCM mode. The symmetric key $K_s$ is then established via an Elliptic Curve Diffie-Hellman (ECDH) key exchange, with the server’s public key embedded in the malware.

$$Ciphertext, Tag = Enc_{AES-256-GCM}(K_s, IV, P)$$
$$SharedSecret = ECDH(SK_{client}, PK_{server})$$
$$K_s = KDF(SharedSecret)$$

Critical Implementation Flaw:
Our laboratory identified a Server-Side Key Reuse flaw. The actors have reused the same static ECDH key pair across multiple M3rx campaigns. This means the server’s private key, $SK_{server}$, is constant. By analyzing the encrypted files from a single victim, Lockbit Decryptor can launch a Known-Plaintext Attack (KPA) by guessing common file headers (e.g., \xD0\xCF\x11\xE0 for older Office files). With enough known plaintext, we can solve for the shared secret and subsequently derive the AES key, bypassing the need for the client’s ephemeral key.

IT ADMIN TOOLKIT (POWERSHELL AUDIT)

Deploy this script to conduct a thorough sweep for M3rx-related IOCs across your fleet.

# Lockbit Decryptor Audit Script for M3rx Variant
Write-Host "Initiating forensic sweep for M3rx IOCs..." -ForegroundColor DarkMagenta

# 1. Detect Randomized Services Installed Recently
Get-CimInstance -ClassName Win32_Service | Where-Object {
    ($_.State -eq 'Running') -and 
    ($_.StartTime -gt (Get-Date).AddDays(-3)) -and
    ($_.PathName -match '%ProgramData%' -or $_.DisplayName -notmatch '^[a-zA-Z]')
} | Select-Object Name, DisplayName, PathName, ProcessId, State

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

# 3. Check for Persistence via Run Policies
New-PSDrive -PSProvider Registry -Root HKLM -Name HKLM
Get-ChildItem "HKLM:\SOFTWARE\Microsoft\Windows\CurrentVersion\Run" -ErrorAction SilentlyContinue | 
    Get-ItemProperty | Where-Object { $_.PSObject.Properties.Value -match '%ProgramData%' } | 
    Select-Object -ExpandProperty Property | ForEach-Object {
        Write-Output "Run Key: $_`: $(Get-ItemPropertyValue -Path 'HKLM:\...\Run' -Name $_)"
    }

RECOVERY PATHWAYS & CTA

Contrasting Recovery Strategies:

• Professional Key Reconstruction: Lockbit Decryptor leverages the Server-Side Key Reuse flaw. Through computational analysis of the encrypted fileset, we reliably reconstruct the AES keys, achieving total decryption without engaging the adversaries.
• Forensic Memory Acquisition: If a live memory dump was captured during triage, our lab can extract the ECDH parameters directly from the process space, providing an alternative recovery path.
• Public Resources: No public decryptors are currently available for M3rx due to the complexity of its key generation and the need for the reused server key.
• FINAL RECOMMENDATION: Refrain from contacting the actors via their Tor site or Tox ID. Negotiations fund illicit activities and offer no guarantee of success. Their threats about data publication are standard pressure tactics. Submit a case to Lockbit Decryptor for expert analysis and guaranteed, silent restoration of your SQL databases (.mdf), virtual disks (.vhd, .vhdx, .vmdk), and all other mission-critical assets.

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

Frequently Asked Questions (FAQ)

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