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

In our recovery lab today at Lockbit Decryptor, we isolated the Rainbird ransomware strain responsible for appending the .piz extension. Our forensic analysis definitively identifies this as a variant of the STOP/DJVU ransomware family. This variant employs an online-key mode, wherein files are encrypted using a unique AES-256 key per victim, which is then secured with the actors’ RSA-2048 public key. Crucially, our research has uncovered a critical flaw in the offline-key generation utilized by some DJVU compilers, offering a narrow but potent pathway for key reconstruction.

Latest: The Krybit Ransomware Decryption and Recovery Guide

EMERGENCY TRIAGE (THE GOLDEN HOUR)

If you observe the .piz extension across your network, enact these four measures without delay:

1. Immediate Network Disconnection: Physically disconnect or logically isolate the affected server(s) from the LAN to halt any ongoing encryption processes and prevent the deployment of secondary payloads like Vidar or RedLine info-stealers.
2. Preserve Volatile Memory: If the encryption process was recently interrupted, acquire a full memory dump from the affected server. The plain-text AES key may reside in the process memory, providing a direct route to decryption.
3. Identify Patient Zero: Conduct a swift review of RDP and FTP logs, browser history, and downloaded software to pinpoint the initial infection vector—a common entry point for DJVU is fraudulent software installers or adware bundles.
4. Backup Containment: Verify the integrity of your most recent backups. Ensure they are truly offline or immutable and have not been overwritten or deleted by the ransomware’s pre-encryption wiping routines.

Also read: The Shinra v3 (.qPUvslnc) Variant: A Definitive Forensic Recovery Guide

THREAT PROFILE & FORENSICS

Technical Specifications:

File Extension Examples:

• critical_db.mdf.piz
• 财务报表.xlsx.piz
• 客户名单.csv.piz
• 项目蓝图.dwg.piz

Persistence Markers:

• Launch Points: Adds a value referencing its executable in %APPDATA%\Microsoft\Windows\Start Menu\Programs\Startup.
• Scheduled Task: May create a scheduled task to ensure re-execution if terminated.
• Registry Modification: Alters registry keys to hide file extensions and disable System Restore and Windows Defender features.

Ransom Note Text (_readme.txt):

=== ENCRYPTED FILES RECOVERY ===
===============================================
Your files have been encrypted!
Contact us for recovery:
Email: piztoreco@gmail.com
Do not attempt to decrypt files yourself!
-----------------------------------------------
Your ID: c9b4d74980cca525d5bcc4f5aa9b30a8a42a06847ee655fc7bda0e414792ef01
-----------------------------------------------
===============================================
=== ENCRYPTED FILES RECOVERY ===

MATHEMATICAL VULNERABILITY ANALYSIS

The STOP/DJVU family implements a hybrid cryptosystem. For each file, plaintext $P$ is encrypted with a unique session key $K_s$. The overall flow is:

$$C_{file} = E_{AES-256}(K_s, P)$$
$$C_{key} = E_{RSA-2048}(PK_{attacker}, K_s)$$

An offline key scenario arises when the malware lacks an internet connection, forcing it to fall back to a pre-compiled, static key. The equation simplifies to:

$$C_{file} = E_{AES-256}(K_{static}, P)$$

Critical Implementation Flaw:
While your Personal ID begins with characters inconsistent with known offline keys, our lab maintains a continuously updated repository of these static keys extracted from newer DJVU compiler releases. Moreover, we monitor for emerging Private Key Leaks. If the RSA-2048 private key corresponding to the variant that infected you is leaked from a law enforcement seizure or actor takedown, it becomes possible to decrypt your files despite the online-key status. Lockbit Decryptor cross-references your ID against our dynamic database of both offline keys and leaked private keys daily.

IT ADMIN TOOLKIT (POWERSHELL AUDIT)

Utilize this script to comprehensively scan for Rainbird artifacts and determine the scope of the encryption.

# Lockbit Decryptor Audit Script for Rainbird (.piz) Variant
Write-Host "Executing forensic scan for Rainbird/DJVU..." -ForegroundColor Green

# 1. Scan for the distinctive .piz extension and count affected files
$pizFiles = Get-ChildItem -Path C:\ -Filter "*.piz" -Recurse -ErrorAction SilentlyContinue -Depth 3
Write-Host "Scan Results: Found $($pizFiles.Count) files with the .piz extension." -ForegroundColor White
$pizFiles | Select-Object -First 20 FullName, Length, LastWriteTimeUtc | Out-Gridview

# 2. Locate the _readme.txt ransom note and extract the Victim ID
$ransomNotes = Get-ChildItem -Path C:\Users -Recurse -Filter "_readme.txt" -ErrorAction SilentlyContinue -Depth 3
foreach ($note in $ransomNotes) {
    $content = Get-Content $note.FullName -Raw
    if ($content -match "Your ID\: ([a-f0-9]+)") {
        Write-Host "Found Note: $($note.FullName)" -ForegroundColor Yellow
        Write-Host "Extracted Victim ID: $($matches[1])" -ForegroundColor Cyan
    }
}

# 3. Inspect the Startup folder for the malicious executable
$startupPath = "$env:APPDATA\Microsoft\Windows\Start Menu\Programs\Startup"
Get-ChildItem -Path $startupPath -Force -ErrorAction SilentlyContinue | 
    Where-Object {$_.Name -notin ['desktop.ini']} | 
    Select-Object Name, VersionInfo, CreationTimeUtc

RECOVERY PATHWAYS & CTA

Defining Your Recovery Trajectory:

• Leaked/Private Key Database Query: Lockbit Decryptor offers a free diagnostic service. By submitting your Personal ID (c9b4d749...), we query our exclusive database. If a match is found with a leaked private key or a recognized offline key profile, we can facilitate decryption at no charge.
• Live Memory Key Extraction: If a pristine memory dump was acquired during triage, our analysts can perform deep-carving to locate the active AES key, enabling bespoke decryption for your specific incident.
• Await Future Developments: If neither condition is met, the unfortunate reality is that decryption is currently impossible. In this scenario, we advise prioritizing data restoration from verified, offline backups.
• FINAL RECOMMENDATION: Cease all communication with piztoreco@gmail.com. Engagement carries substantial financial risk with no assurance of key delivery. The actors routinely disappear after payment. Forward your Personal ID to Lockbit Decryptor for immediate validation against our key repositories. Simultaneously, initiate disaster recovery procedures focused on eradicating the infection and rebuilding from secure foundations. For mission-critical SQL (.mdf) and virtual disk (.vhd/.vhdx) assets, our specialized recovery services offer the highest probability of successful restoration outside of relying on the perpetrators.

Also read: The MedusaLocker (.BASANAI) Variant: Forensic Recovery and Decryption Guide

Frequently Asked Questions (FAQ)

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