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Backdoor.Win64.SILENTLYNX.THBOFBE

April 17, 2025
 Analysis by: Leidryn Saludez
 ALIASES:

Gen:Variant.Zusy.570685 (BITDEFENDER)

 PLATFORM:

Windows

 OVERALL RISK RATING:
 DAMAGE POTENTIAL:
 DISTRIBUTION POTENTIAL:
 REPORTED INFECTION:
 INFORMATION EXPOSURE:

  • Threat Type: Backdoor

  • Destructiveness: No

  • Encrypted: No

  • In the wild: Yes

  OVERVIEW

Infection Channel:

Downloaded from the Internet, Dropped by other malware

This Backdoor arrives on a system as a file dropped by other malware or as a file downloaded unknowingly by users when visiting malicious sites.

  TECHNICAL DETAILS

File Size:

122,368 bytes

File Type:

EXE

Initial Samples Received Date:

06 Feb 2025

Payload:

Drops files

Arrival Details

This Backdoor arrives on a system as a file dropped by other malware or as a file downloaded unknowingly by users when visiting malicious sites.

Installation

This Backdoor drops the following files:

  • %Pictures%\ESET.txt → contains current date (YYYY-MM-DD)
  • %Pictures%\Test
  • %Pictures%\{Computer Name}_C_{Current Date}.zip
  • %Pictures%\{Computer Name}_D_{Current Date}.zip

It adds the following processes:

  • %System%\cmd.exe /c "powershell.exe -NoProfile -ExecutionPolicy Bypass -e {Base64 Encoded Command}"

(Note: %System% is the Windows system folder, where it usually is C:\Windows\System32 on all Windows operating system versions.)

  SOLUTION

Minimum Scan Engine:

9.800

FIRST VSAPI PATTERN FILE:

19.886.03

FIRST VSAPI PATTERN DATE:

07 Feb 2025

VSAPI OPR PATTERN File:

19.887.00

VSAPI OPR PATTERN Date:

08 Feb 2025

Step 1

Trend Micro Predictive Machine Learning detects and blocks malware at the first sign of its existence, before it executes on your system. When enabled, your Trend Micro product detects this malware under the following machine learning name:

     TROJ.Win32.TRX.XXPE50FFF090

Step 2

Before doing any scans, Windows 7, Windows 8, Windows 8.1, and Windows 10 users must disable System Restore to allow full scanning of their computers.

Step 3

Note that not all files, folders, and registry keys and entries are installed on your computer during this malware's/spyware's/grayware's execution. This may be due to incomplete installation or other operating system conditions. If you do not find the same files/folders/registry information, please proceed to the next step.

Step 4

Search and delete this file

[ Learn More ]
There may be some files that are hidden. Please make sure you check the Search Hidden Files and Folders checkbox in the "More advanced options" option to include all hidden files and folders in the search result.  
  • %Pictures%\ESET.txt → contains current date (YYYY-MM-DD)
  • %Pictures%\Test
  • %Pictures%\{Computer Name}_C_{Current Date}.zip
  • %Pictures%\{Computer Name}_D_{Current Date}.zip

Step 5

Scan your computer with your Trend Micro product to delete files detected as Backdoor.Win64.SILENTLYNX.THBOFBE. If the detected files have already been cleaned, deleted, or quarantined by your Trend Micro product, no further step is required. You may opt to simply delete the quarantined files. Please check the following Trend Micro Support pages for more information:


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