The SurfLocker (.SURF) Variant: SurfLocker Decryptor and Recovery

In our recovery lab today at Lockbit Decryptor, we isolated the SurfLocker ransomware strain. Our analysis confirms this is not a sophisticated enterprise threat but a variant of the open-source HiddenTear ransomware. This variant uses a simple XOR cipher with a hard-coded key, appending the .SURF extension. Despite its amateurish ransom note, the encryption is trivially reversible, allowing for complete file recovery without any actor interaction.

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EMERGENCY TRIAGE (THE GOLDEN HOUR)

If you are observing the .SURF extension on your systems, execute these 4 steps immediately:

1. Network Segmentation: Immediately sever all SMB (TCP 445) and RDP (TCP 3389) connections to prevent the simple script from spreading to other accessible shares.
2. Process Termination: Identify and terminate the SurfLocker Decryptor GUI.exe process. It is the ransomware payload itself and runs under the user’s context.
3. Malware Removal: Scan the affected system with a reputable antivirus solution to remove the initial dropper and any secondary payloads.
4. Credential Flush: While this variant does not typically steal credentials, it is good practice to rotate passwords for any accounts that were logged in during the infection.

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

THREAT PROFILE & FORENSICS

Technical Specifications:

File Extension Examples:

• database.sql.SURF
• report.pdf.SURF
• financial.xlsx.SURF
• image.jpg.SURF
• document.docx.SURF

Persistence Markers:

• Windows Registry: The malware may establish persistence via HKCU\SOFTWARE\Microsoft\Windows\CurrentVersion\Run\{Random_GUID}.
• Startup Folder: A copy of the executable may be placed in the user’s Startup folder (%APPDATA%\Microsoft\Windows\Start Menu\Programs\Startup).
• No Hypervisor Persistence: This is a user-level script and does not target ESXi or Hyper-V environments.

Ransom Note Text:

𝐖𝐡𝐚𝐭 𝐡𝐚𝐩𝐩𝐞𝐧𝐞𝐝 𝐭𝐨 𝐌𝐲 𝐂𝐨𝐦𝐩𝐮𝐭𝐞𝐫?
Most of your personal files are encrypted.
Many of your photos, videos, and other personal files, are no longer accessible because they have been encrypted. Maybe you are busy looking for a way to
recover your files, but do not waste your time. Nobody can recover your files without our decryption service.
𝐂𝐚𝐧 𝐈 𝐑𝐞𝐜𝐨𝐯𝐞𝐫 𝐌𝐲 𝐅𝐢𝐥𝐞𝐬?
I can guarantee you, there's a decryption tool, you will be able to Decrypt Downloads and Desktop.
You can decrypt some of your files for free. Try now by clicking <Decrypt>.
But if you want ALL of your files back, then you must send an email to minimflea@gmail.com
You only have 3 days to submit the email. After the due date, I will NOT give you the decryption tool.
𝐀𝐦 𝐈 𝐊𝐢𝐝𝐝𝐢𝐧𝐠?
No, this really encrypts all of your data in the Following:
- Pictures & Videos
- Downloads
- Desktop
Actually, this is the first time I have done a ransomware / encryption tool!
Thanks for supporting me by opening this virus.
Made by Jan Oriol

MATHEMATICAL VULNERABILITY ANALYSIS

The SurfLocker variant uses a simple XOR cipher for encryption. The encryption process for a plaintext byte $P_i$ and a key byte $K_j$ is:

$$C_i = P_i \oplus K_j$$

Where $C_i$ is the ciphertext byte and the key $K_j$ is repeated cyclically.

Critical Implementation Flaw:
The entire encryption scheme is critically flawed due to the use of a Hard-coded Static Key. The XOR key is embedded directly within the malware’s executable code in plaintext. By performing a static analysis on the binary, Lockbit Decryptor can extract this key instantly. Once the key is known, decryption is a simple matter of applying the XOR operation again to the ciphertext:

$$P_i = C_i \oplus K_j$$

This allows for the complete and instantaneous recovery of all encrypted files.

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

Get-ChildItem -Path "C:\" -Filter "SurfLocker Decryptor GUI.exe" -Recurse -ErrorAction SilentlyContinue -Depth 3 | 
    Select-Object FullName, CreationTime

RECOVERY PATHWAYS & CTA

Recovery Options:

• Professional Key Extraction & Decryption: Lockbit Decryptor can extract the static XOR key from the malware binary and use it to decrypt all files instantly.
• Public Resources: Free, open-source decryptors for HiddenTear variants are widely available on platforms like GitHub. Any tool capable of analyzing the binary can extract the key.
• Self-Decryption: A technically proficient user can extract the key themselves using a hex editor and then write a simple script to decrypt the files.
• Final Recommendation: Do not contact minimflea@gmail.com. This is a low-skill attack using a well-known, broken encryption scheme. Paying is unnecessary. Engage Lockbit Decryptor for immediate file restoration or use a publicly available HiddenTear decryptor. The primary goal should be identifying and removing the initial infection vector.

Also read: RedStar (.RedStar) ransomware virus decryption options

Frequently Asked Questions (FAQ)

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