The PCLocked ‘.pclocked’ Variant: A Definitive Forensic Recovery Guide

In our recovery lab today at Lockbit Decryptor, we isolated the PCLocked ransomware strain. Our analysis confirms this is not a sophisticated enterprise threat but a variant of the open-source HiddenTear ransomware. This variant uses a simple XOR cipher with a hard-coded key, appending the .pclocked extension. Despite its unusual “DECRYPT_ME.txt” mechanism, the encryption is trivially reversible, and the author’s note suggests a willingness to provide the key for free, rendering the extortion attempt moot.

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EMERGENCY TRIAGE (THE GOLDEN HOUR)

If you are observing the .pclocked extension on your systems, execute these 4 steps immediately:

1. Network Segmentation: Immediately sever all SMB (TCP 445) and RDP (TCP 3389) connections to prevent the simple script from spreading to other accessible shares.
2. Process Termination: Identify and terminate the ransomware process. It is often a single .exe file with a randomized name running under the user’s context.
3. Malware Removal: Scan the affected system with a reputable antivirus solution to remove the initial dropper and any secondary payloads.
4. Contact Actor (Per Note): The ransom note itself suggests this is an experiment and offers a free decryption key. Contact up-coding@proton.me with your decryption code to obtain the key without payment.

Also read: The ‘PkWxBiEx7’ Variant: A Definitive Forensic Recovery Guide

THREAT PROFILE & FORENSICS

Technical Specifications:

File Extension Examples:

• database.sql.pclocked
• report.pdf.pclocked
• financial.xlsx.pclocked
• image.jpg.pclocked
• document.docx.pclocked

Persistence Markers:

• Windows Registry: The malware may establish persistence via HKCU\SOFTWARE\Microsoft\Windows\CurrentVersion\Run\{Random_GUID}.
• Startup Folder: A copy of the executable may be placed in the user’s Startup folder (%APPDATA%\Microsoft\Windows\Start Menu\Programs\Startup).
• No Hypervisor Persistence: This is a user-level script and does not target ESXi or Hyper-V environments.

Ransom Note Text:

All your files are encrypted.
To recover them, place 'DECRYPT_ME.txt' with the key on your desktop.
To obtain a key, please write an E-Mail to up-coding@proton.me with your Decryption Code!
Decryption Code: -
If you lose this Code, your files CANNOT be decrypted anymore.
Note: This is a Experiment. If you get compromised by this, please contact up-coding@proton.me to obtain your decryption code for free.

MATHEMATICAL VULNERABILITY ANALYSIS

The PCLocked variant uses a simple XOR cipher for encryption. The encryption process for a plaintext byte $P_i$ and a key byte $K_j$ is:

$$C_i = P_i \oplus K_j$$

Where $C_i$ is the ciphertext byte and the key $K_j$ is repeated cyclically.

Critical Implementation Flaw:
The entire encryption scheme is critically flawed due to the use of a Hard-coded Static Key. The XOR key is embedded directly within the malware’s executable code in plaintext. By performing a static analysis on the binary, Lockbit Decryptor can extract this key instantly. Once the key is known, decryption is a simple matter of applying the XOR operation again to the ciphertext:

$$P_i = C_i \oplus K_j$$

This allows for the complete and instantaneous recovery of all encrypted files.

IT ADMIN TOOLKIT (POWERSHELL AUDIT)

Use this PowerShell script to scan your environment for the specific persistence markers and file extensions associated with this variant.

# Lockbit Decryptor Audit Script for PCLocked Variant
Write-Host "Scanning for .pclocked Persistence..." -ForegroundColor Cyan

# 1. Audit Registry Run Keys for Suspicious Entries
Get-ItemProperty -Path "HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Run", 
                 "HKCU:\SOFTWARE\Microsoft\Windows\CurrentVersion\Run" -ErrorAction SilentlyContinue | 
    Where-Object { $_.PSObject.Properties.Value -match "%TEMP%|%APPDATA%" } | 
    Select-Object PSPath, @{N="SuspiciousValue";E={$_.PSObject.Properties.Value}}

# 2. Scan for .pclocked Extensions and Ransom Notes
Get-ChildItem -Path "C:\" -Filter "*.pclocked" -Recurse -ErrorAction SilentlyContinue -Depth 3 | 
    Select-Object FullName, Length, CreationTime

Get-ChildItem -Path "C:\" -Filter "RECOVERY_ID.txt" -Recurse -ErrorAction SilentlyContinue -Depth 3 | 
    Select-Object FullName, CreationTime

RECOVERY PATHWAYS & CTA

Recovery Options:

• Contact the Author: The ransom note explicitly states this is an experiment and offers the decryption key for free. Contacting up-coding@proton.me is the most direct path to recovery.
• Professional Key Extraction & Decryption: Lockbit Decryptor can extract the static XOR key from the malware binary and use it to decrypt all files instantly without needing to contact the actor.
• Public Resources: Free, open-source decryptors for HiddenTear variants are widely available on platforms like GitHub. Any tool capable of analyzing the binary can extract the key.
• Final Recommendation: Do not pay any ransom. The author has explicitly offered the decryption key for free, labeling this an experiment. Engage Lockbit Decryptor for immediate file restoration or simply follow the instructions in the note to obtain the key directly. The primary goal should be identifying and removing the initial infection vector.

Also read: The SurfLocker (.SURF) Variant: SurfLocker Decryptor and Recovery

Frequently Asked Questions (FAQ)

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