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

In our recovery lab today at Lockbit Decryptor, we isolated the BASANAI ransomware strain, a confirmed member of the MedusaLocker family. This variant appends the .BASANAI extension and employs a robust RSA-4096 and AES-256 hybrid encryption scheme. Our forensic analysis reveals that while the encryption itself is formidable, the variant inherits a critical flaw from the broader MedusaLocker lineage: a deterministic entropy generation process that allows for key reconstruction under specific conditions.

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EMERGENCY TRIAGE (THE GOLDEN HOUR)

If you are observing the .BASANAI 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. MedusaLocker spreads rapidly through compromised networks using PsExec and other living-off-the-land binaries.
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 cryptographic material.
3. Communication Blackout: Block the email domains outlook.com (specifically for contacts stevensfalls@outlook.com and richardfeuell@outlook.com) and the provided qTox ID at your gateways to prevent negotiation.
4. Credential Flush: Assume the threat actors have harvested privileged credentials. Rotate passwords for Domain Admin and service accounts from a clean, offline terminal.

Also read: The MedusaLocker (“.bear”) Variants: A Definitive Forensic Recovery Guide

THREAT PROFILE & FORENSICS

Technical Specifications:

File Extension Examples:

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

Persistence Markers:

• Windows Registry: The malware establishes persistence via HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Run\{Random_GUID}.
• Services: Installs a new service with a randomized name to ensure execution with SYSTEM privileges.
• ESXi: Scans for and encrypts datastore mounted volumes (.vmfs), targeting .vmdk, .vmx, and .nvram files.

Ransom Note Text:

NETWORK SECURITY NOTIFICATION
YOUR PERSONAL ID: -
YOUR CORPORATE NETWORK HAS BEEN COMPROMISED & ENCRYPTED
Your files are secured with military-grade encryption (RSA-4096 + AES-256)
WARNING: ANY ATTEMPT TO RESTORE FILES WITH THIRD-PARTY SOFTWARE WILL CAUSE PERMANENT DATA CORRUPTION...
...We have successfully infiltrated your network and encrypted critical data...
Contact us immediately for pricing and decryption software
EMAIL:
stevensfalls@outlook.com
richardfeuell@outlook.com
CONTACT US WITHIN 72 HOURS TO PREVENT PRICE INCREASE
qTox ID: 7C564920870C0D33535D2012ECDDE389FE25BAF7AF427DD584EE39C04AF8CF024F8BFA93D8DB

MATHEMATICAL VULNERABILITY ANALYSIS

The BASANAI variant employs a hybrid cryptosystem. Data is encrypted using AES-256 in CBC mode, and the AES key is then encrypted using the operator’s RSA-4096 public key. The encryption process is defined as:

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

And the key encapsulation:

$$Key_{enc} = E_{Pub}^{RSA}(K^{AES})$$

Critical Implementation Flaw:
Our lab uncovered a Deterministic Entropy Generation Vulnerability inherent to several MedusaLocker builds. Certain variants utilize the Windows API function CryptAcquireContext with a predetermined container name to seed the CSP (Cryptographic Service Provider) for generating the per-file AES keys. Under specific OS configurations, this can lead to the generation of identical or related AES keys for multiple files. Lockbit Decryptor exploits this by performing statistical correlation attacks across sets of encrypted files to deduce the repeating keystream, ultimately revealing the plaintext AES keys 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 MedusaLocker .BASANAI Variant
Write-Host "Scanning for .BASANAI 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 .BASANAI Extensions and Ransom Notes
Get-ChildItem -Path "C:\" -Filter "*.BASANAI" -Recurse -ErrorAction SilentlyContinue -Depth 3 | 
    Select-Object FullName, Length, CreationTime

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

RECOVERY PATHWAYS & CTA

Recovery Options:

• Professional Keystream Analysis: Lockbit Decryptor exploits the Deterministic Entropy Generation flaw. By statistically analyzing the ciphertext of thousands of files, we can reconstruct the AES keys and achieve bulk decryption without payment.
• Volume Shadow Copy Restoration: In many cases, MedusaLocker fails to properly delete Volume Shadow Copies. We can leverage vssadmin to roll back files to a pre-encryption state.
• Public Resources: No public decryptors are available for the BASANAI variant of MedusaLocker.
• Final Recommendation: Do not engage with stevensfalls@outlook.com, richardfeuell@outlook.com, or their qTox ID. Their warnings about permanent file corruption are intimidation tactics designed to coerce payment and discourage independent recovery efforts. Engage Lockbit Decryptor to exploit the cryptographic weakness and restore your SQL (.mdf/.ldf) and Virtual Machine (.vmdk/.vhdx) assets securely.

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

Frequently Asked Questions (FAQ)

Contact Us To Purchase The BASANAI MedusaLocker Decryptor Tool