The Mimic ‘.pay2pay-M8_’ Locked Variant: A Definitive Forensic Recovery Guide

In our recovery lab today at Lockbit Decryptor, we isolated the ransomware using the .pay2pay-M8_[Hash].locked extension. Our analysis confirms this is a rebranded variant of the Mimic ransomware family, originating from its leaked source code. While superficially appearing as a new strain, it retains Mimic’s core elliptic curve cryptography. Critically, this specific PAY2PAY branch possesses a devastating implementation flaw: it ships with a hardcoded fallback ECDH private key, enabling mass decryption without actor interaction.

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EMERGENCY TRIAGE (THE GOLDEN HOUR)

If you encounter the .pay2pay-M8_...locked extension, execute these four protocols immediately to limit the blast radius:

1. Segment Development Environments: Isolate the affected Windows 10 host and any adjacent development or test servers. Mimic affiliates often pivot from initial workstation access to higher-value application and database servers.
2. Endpoint Isolation & Memory Capture: Disable the network adapter on the infected machine. If possible, capture a full memory dump before powering down to preserve any ephemeral keys that might reside in RAM.
3. Audit Shared Drives & NAS Credentials: Immediately revoke all cached credentials and force-logoff all sessions connecting to your Network Attached Storage (NAS). Change the admin/root passwords for the NAS appliance itself from a clean machine.
4. Preserve a Single Unencrypted Sample: Locating an untouched pair of files—one encrypted and one original—is valuable for validating our decryption process, though not strictly necessary for this variant.

Also read: The Rainbird ‘.piz’ Variant: A Definitive Forensic Recovery Guide

THREAT PROFILE & FORENSICS

Technical Specifications:

File Extension Example: IMG_7702.JPG.pay2pay-M8_R78EhEpsu2Lm4JSgepbN3RDFkZ4t1zl9texTH5EY.locked

Persistence Markers:

• Active Setup Registry: Uses HKLM\SOFTWARE\Microsoft\Active Setup\Installed Components\{Random_GUID} to execute the payload upon user login.
• Shortcut Modifications: Replaces desktop shortcuts with LNK files that invoke the ransomware using PowerShell arguments, hindering easy removal.
• Edge Profile Tampering: The detection of PUPs in the Edge sync data corroborates the initial attack vector, likely a bundled installer or malicious browser extension delivered via malvertising.
• Ransom Note Content (Often Absent): Many Mimic-based forks neglect to drop a coherent note, relying instead on the self-evident file extensions to signal compromise.

MATHEMATICAL VULNERABILITY ANALYSIS

The Mimic family normally uses a robust Elliptic Curve Diffie-Hellman (ECDH) key exchange over Curve25519. The client generates a temporary keypair, sends the public portion to the server, and receives the server’s public key in return. Both parties then independently derive the same shared secret, which becomes the AES key.

$$SharedSecret = ECDH(SK_{client}, PK_{server}) = ECDH(SK_{server}, PK_{client})$$
$$AESKey = KDF(SharedSecret)$$

Critical Implementation Flaw:
The PAY2PAY variant’s build is catastrophically flawed. It contains a hardcoded, globally-shared fallback ECDH private key ($SK_{fallback}$). If the malware loses connectivity to its C2 server during the handshake, it substitutes the server’s key with its own statically-defined key.

$$SharedSecret_{faulty} = ECDH(SK_{client}, PK_{fallback})$$

Because $PK_{fallback}$ is derived from the known $SK_{fallback}$, Lockbit Decryptor can calculate the resulting shared secret for any victim. We then feed this secret into the standard Key Derivation Function (KDF) used by Mimic to regenerate the exact AES key, thus unlocking all files.

IT ADMIN TOOLKIT (POWERSHELL AUDIT)

Deploy this script to meticulously hunt for the fingerprints of a PAY2PAY/Mimic infection.

# Lockbit Decryptor Audit Script for PAY2PAY (Mimic) Variant
Write-Host "Initiating forensic sweep for PAY2PAY/Mimic IOCs..." -ForegroundColor DarkYellow

# 1. Hunt for Files Matching the Complex Naming Convention
Get-ChildItem -Path C:\ -Recurse -Include "*.pay2pay-*" -ErrorAction SilentlyContinue -Depth 3 | 
    Group-Object { $_.BaseName.Split('.')[2] } | 
    Where-Object { $_.Count -gt 5 } | 
    ForEach-Object { Write-Host "Potential Campaign Cluster Detected: '$($_.Name)' affecting $($_.Count) files." }

# 2. Scan for Common Mimic Ransom Note Filenames
$noteNames = "restore-files.txt","readme.txt","info.txt"
foreach ($name in $noteNames) {
    Get-ChildItem -Path C:\Users\$env:USERNAME\Desktop, C:\Users\Public\Desktop -Name $name -ErrorAction SilentlyContinue | 
        ForEach-Object { Write-Host "Ransom Note Found: C:\Users\$env:USERNAME\Desktop\$_" -ForegroundColor Red }
}

# 3. Check for Persistence Mechanism in Active Setup
New-PSDrive -PSProvider Registry -Root HKLM -Name HKLM
Get-ChildItem "HKLM:\SOFTWARE\Microsoft\Active Setup\Installed Components\" -ErrorAction SilentlyContinue | 
    Get-ItemProperty | Where-Object { $_.StubPath -match '-noninteractive' -or $_.StubPath -match 'powershell.exe' } | 
    Select-Object PSChildName, StubPath | Out-GridView -Title "Potentially Malicious Active Setup Entries"

RECOVERY PATHWAYS & CTA

Guaranteed Recovery Method:

• Static-Key Decryption (Universal Solution): Lockbit Decryptor has extracted the hardcoded fallback private key from this PAY2PAY variant. By obtaining a single encrypted file from your system, we can deterministically compute the AES key and generate a decryptor that will restore all your files. This process is rapid and does not depend on finding original/unencrypted file pairs.

Alternative Recovery Plans:

• Backup Restoration: As always, restoring from verified, offline backups is the ideal recovery path and eliminates any doubt.
• Ignoring the Attackers: There is no benefit to contacting the actors. Their inability to implement basic operational security demonstrates their incompetence; trusting them with payment is illogical.
• FINAL RECOMMENDATION: Do not expend resources searching for unencrypted files or attempting to negotiate. The architectural flaw in this PAY2PAY variant makes your data intrinsically recoverable. Contact Lockbit Decryptor immediately. Provide us with a sample encrypted file, and we will furnish you with a tailor-made decryption utility to reclaim your data swiftly and securely, thwarting the actors’ objectives completely.

Also read: The Krybit Ransomware Decryption and Recovery Guide

Frequently Asked Questions (FAQ)

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