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Backdoor.Win32.EXPLORAT.A

February 09, 2021
 Analysis by: Patrick Noel Collado
 ALIASES:

Backdoor.Win32.Agent.mytufe (Kaspersky), Win32/Agent.UAG trojan (Nod32)

 PLATFORM:

Windows

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

  • Threat Type: Backdoor

  • Destructiveness: No

  • Encrypted:

  • In the wild: Yes

  OVERVIEW

Infection Channel:

Downloaded from the Internet


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.

It executes commands from a remote malicious user, effectively compromising the affected system.

  TECHNICAL DETAILS

File Size:

382,788 bytes

File Type:

EXE

Memory Resident:

Yes

Initial Samples Received Date:

29 Jan 2021

Payload:

Connects to URLs/IPs, Terminates processes

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 adds the following folders:

  • %Windows%\Web\sysHelp\
  • %Windows%\Web\sysHelp\cpl
  • %Windows%\Web\sysHelp\cpc

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

It drops the following files:

  • %Windows%\Web\canaccess.tmp
  • %Windows%\Web\sysHelp\{username}.tc.ada

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

It adds the following processes:

  • cmd /c reg query "HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion" /v ProductName
  • cmd /c type "C:\Windows\web\canaccess.tmp"
  • cmd /c del /q "C:\Windows\web\canaccess.tmp"

It terminates itself if it finds the following processes in the affected system's memory:

  • OllyDbg
  • PhantOm
  • PEBrowse
  • Xamarin
  • Immunity

Backdoor Routine

This Backdoor executes the following commands from a remote malicious user:

  • EOF – End of transmitted file
  • EndTask – Terminate a specified process
  • V – Kill explosive process and delete traces(?)
  • K – Terminate explosive process
  • R – Restart explosive process
  • FileSend – Send a specified file
  • CloseFile – Close a specified file
  • OpenPF – Open a specified file
  • RunCMD – Run a specified command line
  • EnumKeys – Get the registry keys under a specified path
  • EnumRootKeys – Get root registry keys
  • GetRegValue – Get a specified registry value.
  • Telnet – connect remotely
  • Size – Get size of a specified file
  • AddDir – Create a specified directory
  • DelDir – create a specified directory
  • ListProcess – List all running processes
  • KillProcess – Terminate a specified process
  • GetDrivesFolders – Get the content of a specific folder
  • GetDrives – Get the drive list
  • GetFiles – Send specific file to C&C
  • ScShot – Get a screenshot
  • DumpPass – Dump saved passwords
  • DumpHist – Dump IE history
  • KeyLog – get latest key logging file content
  • ClipboardLog – get latest clipboard logging file content
  • EnumWindows – List open windows
  • DeleteFiles – Delete specified files
  • CopyPasteFiles – copy and paste specified files
  • CutPasteFiles – cut and paste specified file
  • UnZip – decompress a specified file
  • RenF – Rename file
  • NTCommand – Run ReadSocket function from DLL module

It connects to the following URL(s) to send and receive commands from a remote malicious user:

  • {BLOCKED}.{BLOCKED}.30.40

  SOLUTION

Minimum Scan Engine:

9.800

FIRST VSAPI PATTERN FILE:

16.508.08

FIRST VSAPI PATTERN DATE:

30 Jan 2021

VSAPI OPR PATTERN File:

16.509.00

VSAPI OPR PATTERN Date:

31 Jan 2021

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.XXPE50FFF041

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

Identify and terminate files detected as Backdoor.Win32.EXPLORAT.A

[ Learn More ]
  1. Windows Task Manager may not display all running processes. In this case, please use a third-party process viewer, preferably Process Explorer, to terminate the malware/grayware/spyware file. You may download the said tool here.
  2. If the detected file is displayed in either Windows Task Manager or Process Explorer but you cannot delete it, restart your computer in safe mode. To do this, refer to this link for the complete steps.
  3. If the detected file is not displayed in either Windows Task Manager or Process Explorer, continue doing the next steps.

Step 5

Search and delete these files

[ 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. %Windows%\Web\canaccess.tmp
%Windows%\Web\sysHelp\{username}.tc.ada

Step 6

Search and delete this folder

[ Learn More ]
Please make sure you check the Search Hidden Files and Folders checkbox in the More advanced options option to include all hidden folders in the search result. %Windows%\Web\sysHelp\
%Windows%\Web\sysHelp\cpl
%Windows%\Web\sysHelp\cpc

Step 7

Scan your computer with your Trend Micro product to delete files detected as Backdoor.Win32.EXPLORAT.A. 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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