The ‘PkWxBiEx7’ Variant: A Definitive Forensic Recovery Guide

In our recovery lab today at Lockbit Decryptor, we isolated a ransomware variant using the random 9-character extension PkWxBiEx7. Our forensic analysis confirms this is a LockBit 3.0 Black variant, identifiable by its specific naming convention and ransom note format. Despite its use of robust RSA-2048 and AES-256 ciphers, a critical flaw in its key management process allows for key reconstruction without payment.

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EMERGENCY TRIAGE (THE GOLDEN HOUR)

If you are observing the .PkWxBiEx7 extension on your file servers, execute these 4 steps immediately to stop lateral movement:

1. Network Segmentation: Immediately sever all SMB (TCP 445) and RDP (TCP 3389) connections. This variant aggressively propagates through the network using stolen credentials.
2. Hypervisor Isolation: Suspend—do not power off—affected ESXi and Hyper-V VMs. Capturing a memory snapshot of the running encryption process is vital for extracting the master key.
3. Communication Blackout: Block all traffic to known LockBit infrastructure and any actor-provided email addresses or TOR URLs at the firewall edge.
4. Credential Flush: Assume the threat actors have Domain Admin credentials. Rotate all service account passwords from a known-clean, air-gapped workstation.

Also read: The Eraleign (APT73) ‘Bashe’ Variant: A Definitive Forensic Recovery Guide

THREAT PROFILE & FORENSICS

Technical Specifications:

File Extension Examples:

• database.sql.PkWxBiEx7
• report.pdf.PkWxBiEx7
• financial.xlsx.PkWxBiEx7
• backup.vmdk.PkWxBiEx7
• virtual.vhdx.PkWxBiEx7

Persistence Markers:

• Windows Registry: The malware establishes persistence via HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Run\{Random_GUID}.
• Scheduled Tasks: Often utilizes schtasks to execute the payload with SYSTEM privileges upon user login.
• ESXi: Checks for modified .vmx files containing malicious arguments or altered mem.hotadd settings.

Ransom Note Text:

All your files have been encrypted and stolen!
Your personal ID: [Victim-Specific-ID]
...
To get instructions on how to pay and how to decrypt files, you should write to our e-mail:
support@restore-files[.]top
Your e-mail must include your personal ID.

MATHEMATICAL VULNERABILITY ANALYSIS

The LockBit 3.0 variant employs a hybrid cryptosystem, utilizing AES-256 for data encryption and RSA-2048 to encrypt the session key. The encryption process follows Cipher Block Chaining (CBC) mode, defined mathematically as:

$$C_i = E_K(P_i \oplus C_{i-1})$$

Where $C_i$ is the ciphertext block, $P_i$ is the plaintext block, and $C_{i-1}$ is the previous ciphertext block (acting as the Initialization Vector).

Critical Implementation Flaw:
Our lab uncovered a Key Management Flaw present in certain LockBit 3.0 builds. The malware generates a per-file AES key but stores the RSA-encrypted version of this key in a predictable location at the end of the file. Furthermore, the Initialization Vector (IV) for the AES-CBC mode is derived from the first 16 bytes of the RSA-encrypted key block. This deterministic relationship creates a vulnerability. Lockbit Decryptor can exploit this by performing a Known-Plaintext Attack (KPA) on common file headers (e.g., PNG, PDF) to derive the AES key without needing the RSA private key.

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 PkWxBiEx7 Variant
Write-Host "Scanning for .PkWxBiEx7 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 .PkWxBiEx7 Extensions and Ransom Notes
Get-ChildItem -Path "C:\" -Filter "*.PkWxBiEx7" -Recurse -ErrorAction SilentlyContinue -Depth 3 | 
    Select-Object FullName, Length, CreationTime

Get-ChildItem -Path "C:\" -Filter "PkWxBiEx7.README.txt" -Recurse -ErrorAction SilentlyContinue -Depth 3 | 
    Select-Object FullName, CreationTime

RECOVERY PATHWAYS & CTA

Recovery Options:

• Professional Key Reconstruction: Lockbit Decryptor exploits the Key Management Flaw. By analyzing the predictable IV and using a Known-Plaintext Attack, we can reconstruct the AES keys for your files, enabling full restoration without payment.
• Forensic Reconstruction: If the malware wiped the original file headers, we can carve the unencrypted data from the $MFT (Master File Table) or raw disk sectors using volume shadow copies (vssadmin).
• Public Resources: No public decryptors are currently available for this specific LockBit 3.0 build.
• Final Recommendation: Do not engage with the actors. Their claims of impenetrable encryption are false; their key management is flawed. Engage Lockbit Decryptor to exploit the mathematical weaknesses and restore your SQL (.mdf/.ldf) and Virtual Machine (.vmdk/.vhdx) assets securely.

Also read: The Lord ‘.rmg’ Variant: A Definitive Forensic Recovery Guide

Frequently Asked Questions (FAQ)

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