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

In our recovery lab today at Lockbit Decryptor, we isolated multiple ransomware strains from the MedusaLocker family, collectively identified by the .bearXX extension pattern (where XX varies, e.g., .bear10, .bear20, .bear26, .bear35, .bear50, .bear60). These variants represent ongoing development cycles within the same criminal operation. Despite minor differences, they all employ a robust RSA-2048 and AES-128 hybrid encryption scheme. Our forensic analysis reveals that these variants inherit 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 any .bearXX 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 salamati.vip and amniyat.xyz at your mail gateway to prevent data exfiltration negotiation and further instruction from the actors.
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 Uragan (.uragan) Variant: A Definitive Forensic Recovery Guide

THREAT PROFILE & FORENSICS

Technical Specifications:

File Extension Examples:

• database.sql.bear10
• report.pdf.bear20
• financial.xlsx.bear35
• backup.vmdk.bear50
• virtual.vhdx.bear60

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:

Your personal ID:
-
YOUR COMPANY NETWORK HAS BEEN PENETRATED
Your files are safe! Only modified.(RSA+AES)
ANY ATTEMPT TO RESTORE YOUR FILES WITH THIRD-PARTY SOFTWARE WILL PERMANENTLY CORRUPT IT...
...We gathered highly confidential/personal data...
Contact us for price and get decryption software.
email:
recovery1@salamati.vip
recovery1@amniyat.xyz
IF YOU DON'T CONTACT US WITHIN 72 HOURS, PRICE WILL BE HIGHER.

MATHEMATICAL VULNERABILITY ANALYSIS

These .bearXX variants employ a consistent hybrid cryptosystem. Data is encrypted using AES-128 in CBC mode, and the AES key is then encrypted using the operator’s RSA-2048 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 present across multiple MedusaLocker builds. Several 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 multi-variant family.

# Lockbit Decryptor Audit Script for MedusaLocker .bearXX Variants
Write-Host "Scanning for .bearXX 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 .bearXX Extensions and Ransom Notes
Get-ChildItem -Path "C:\" -Filter "*.bear*" -Include *.bear10,*.bear20,*.bear26,*.bear35,*.bear50,*.bear60 -Recurse -ErrorAction SilentlyContinue -Depth 3 | 
    Select-Object FullName, Length, CreationTime

Get-ChildItem -Path "C:\" -Filter "READ_NOTE.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, regardless of the specific numeric extension, 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 any of the .bearXX variants.
• Final Recommendation: Do not engage with recovery1@salamati.vip or recovery1@amniyat.xyz. Their warnings about permanent file corruption are intended to deter third-party 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 ‘PkWxBiEx7’ Variant: A Definitive Forensic Recovery Guide

Frequently Asked Questions (FAQ)

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