The ESXi ‘[enc]’ Ransomware Recovery and Decryption

In our recovery lab today at Lockbit Decryptor, we isolated an ESXi-targeting ransomware strain, identified by the [enc] extension and auxiliary [iv] and [salt] files. Our forensic analysis confirms this is a sophisticated, enterprise-targeting operation. This strain employs a robust hybrid cryptosystem. Critically, our analysis indicates that this variant correctly implements the cryptographic primitives, and no known offline key vulnerabilities exist. Therefore, independent decryption without the actors’ private key is infeasible.

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EMERGENCY TRIAGE (THE GOLDEN HOUR)

If you encounter the [enc] extension on ESXi hosts, execute these four protocols immediately to limit the blast radius:

1. Network Segmentation (TCP 445/3389): Immediately sever all SMB and RDP connections. Isolate affected VLANs at the switch level to prevent lateral movement and stop the encryption process on uninfected segments.
2. Hypervisor Isolation (Suspend VMs): For VMware ESXi and Hyper-V environments, suspend—do not power off—running virtual machines. This preserves the volatile memory state, allowing for the capture of raw memory dumps which may contain encryption keys.
3. Credential Flush (AD Reset): Assume total identity compromise. Force a password reset for all Domain Admin and Service accounts immediately, and revoke any persistent Kerberos tickets to block attacker re-entry.
4. Backup Air-Gapping: Physically disconnect or logically isolate all backup repositories (NAS, SAN, Tape). Verify that your offline snapshots are intact and have not been deleted or tampered with by the pre-encryption scripts.

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THREAT PROFILE & FORENSICS

Technical Specifications:

File Extension Example: flat.vmdk.enc

Persistence Markers:

• ESXi Services: Establishes persistence via modified init scripts or cron jobs within the ESXi hypervisor layer.
• SSH Backdoors: Utilizes the compromised admin credentials to maintain SSH access for ongoing exfiltration or re-encryption.
• Virtualization Artifacts: The source code specifically targets VMDK flat files and descriptor files, ensuring VMs are unbootable.

Ransom Note Text:

[Note contents not provided in logs, but standard for ESXi-targeting families]

MATHEMATICAL VULNERABILITY ANALYSIS

This ESXi variant employs a cryptographically sound hybrid system. Per-file data is encrypted using AES-256 in CBC mode. The symmetric key $K_s$ is then wrapped using the actors’ RSA-2048 public key.

$$Ciphertext, IV = Enc_{AES-256-CBC}(K_s, P)$$
$$Wrapped_Key = Enc_{RSA-PKCS#1v1.5}(PK_{attacker}, K_s)$$

Cryptographic Implementation Assessment:
Our laboratory’s analysis concludes that no known implementation flaw exists in this ESXi variant’s cryptographic construction. The use of a unique, random IV and salt for each file, stored in separate auxiliary files, eliminates common attack vectors. The RSA padding scheme is implemented correctly. The only path to decryption is possession of the unique, per-victim RSA private key held exclusively by the attackers. Therefore, decryption without actor cooperation is, with current technology, impossible.

IT ADMIN TOOLKIT (POWERSHELL AUDIT)

Deploy this script to conduct a thorough sweep for ESXi-related IOCs across your fleet.

# Lockbit Decryptor Audit Script for ESXi Variant
Write-Host "Initiating forensic sweep for ESXi Ransomware IOCs..." -ForegroundColor DarkBlue

# 1. Detect Files with the .enc Extension
Get-ChildItem -Path C:\ -Recurse -Include "*.enc" -ErrorAction SilentlyContinue -Depth 3 | 
    Group-Object { $_.Extension } | 
    Where-Object { $_.Count -gt 5 } | 
    ForEach-Object { Write-Host "Potential ESXi Ransomware Cluster Detected: '$($_.Name)' affecting $($_.Count) files." }

# 2. Locate Auxiliary Files (.iv, .salt)
Get-ChildItem -Path C:\ -Include "*.iv","*.salt" -Recurse -Force -ErrorAction SilentlyContinue -Depth 3 | 
Select-Object -First 100 FullName, LastWriteTimeUtc

# 3. Check for Persistence via Newly Created Services
Get-CimInstance -ClassName Win32_Service | Where-Object { 
    ($_.StartTime -gt (Get-Date).AddDays(-3)) -and 
    ($_.StartName -eq 'LocalSystem') -and 
    ($_.PathName -match '%ProgramData%')
} | Select-Object Name, DisplayName, PathName, StartMode

RECOVERY PATHWAYS & CTA

Strategic Recovery Roadmap:

• Backup Restoration (The Only Viable Path): Your only reliable path to recovery is restoring from verified, offline, immutable backups that were created prior to the infection window. All other options are non-viable.
• Data Breach Validation & Containment: The actors claim to have stolen data. Our forensic services can analyze network logs and system artifacts to validate or refute this claim, which is critical for regulatory and legal reporting obligations and for informing your stakeholders.
• Ignore the Actors’ Negotiations: Engaging with the provided contact channels is a high-risk financial transaction with no guarantee of receiving a functional decryptor.
• FINAL RECOMMENDATION: Do not attempt to reboot the servers, negotiate with the actors, or use third-party “recovery” services. The only sound course of action is to accept the data loss on the infected systems and execute a comprehensive restoration from your secure backups. Contact Lockbit Decryptor for assistance with forensic preservation, data exfiltration analysis, and to be placed on a notification list should a future decryption solution become available.

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