Analysis by: Mohammed Malubay
ALIASES:

Trojan:Win32/Remcos.PI!MTB(MICROSOFT); a variant of Win32/Injector.ELOX 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

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: 989,698 bytes
File Type: EXE
Memory Resident: Yes
Initial Samples Received Date: 11 May 2020

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:

  • %AppDataLocal%\Vyfw\
  • %Application Data%\remcos\

(Note: %AppDataLocal% is the Local Application Data folder, which is usually C:\Documents and Settings\{user name}\Local Settings\Application Data on Windows 2000(32-bit), XP, and Server 2003(32-bit), or C:\Users\{user name}\AppData\Local on Windows Vista, 7, 8, 8.1, 2008(64-bit), 2012(64-bit) and 10(64-bit).. %Application Data% is the current user's Application Data folder, which is usually C:\Documents and Settings\{user name}\Application Data on Windows 2000(32-bit), XP, and Server 2003(32-bit), or C:\Users\{user name}\AppData\Roaming on Windows Vista, 7, 8, 8.1, 2008(64-bit), 2012(64-bit) and 10(64-bit).)

It drops the following files:

  • %User Temp%\Cab{random numbers}.tmp
  • %User Temp%\Tar{random numbers.tmp
  • %AppDataLocal%\Vyfw\Vyfwset.exe
  • %AppDataLocal%\Vyfw\Vyfw.hta
  • %AppDataLocal%\Vyfw\Fuck
  • %Public%\x.bat
  • %Public%\Natso.bat
  • %Application Data%\remcos\logs.dat

(Note: %User Temp% is the current user's Temp folder, which is usually C:\Documents and Settings\{user name}\Local Settings\Temp on Windows 2000(32-bit), XP, and Server 2003(32-bit), or C:\Users\{user name}\AppData\Local\Temp on Windows Vista, 7, 8, 8.1, 2008(64-bit), 2012(64-bit) and 10(64-bit).. %AppDataLocal% is the Local Application Data folder, which is usually C:\Documents and Settings\{user name}\Local Settings\Application Data on Windows 2000(32-bit), XP, and Server 2003(32-bit), or C:\Users\{user name}\AppData\Local on Windows Vista, 7, 8, 8.1, 2008(64-bit), 2012(64-bit) and 10(64-bit).. %Public% is the folder that serves as a repository of files or folders common to all users, which is usually C:\Users\Public in Windows Vista, 7, and 8.. %Application Data% is the current user's Application Data folder, which is usually C:\Documents and Settings\{user name}\Application Data on Windows 2000(32-bit), XP, and Server 2003(32-bit), or C:\Users\{user name}\AppData\Roaming on Windows Vista, 7, 8, 8.1, 2008(64-bit), 2012(64-bit) and 10(64-bit).)

It adds the following processes:

  • cmd /c ""%Public%\Natso.bat" "
  • reg delete hkcu\Environment /v windir /f
  • reg add hkcu\Environment /v windir /d "cmd /c start /min %Public%\x.bat reg delete hkcu\Environment /v windir /f && REM "
  • schtasks /Run /TN \Microsoft\Windows\DiskCleanup\SilentCleanup /I
  • "%Program Files%\internet explorer\ieinstal.exe"

(Note: %Public% is the folder that serves as a repository of files or folders common to all users, which is usually C:\Users\Public in Windows Vista, 7, and 8.. %Program Files% is the default Program Files folder, usually C:\Program Files in Windows 2000(32-bit), Server 2003(32-bit), XP, Vista(64-bit), 7, 8, 8.1, 2008(64-bit), 2012(64-bit) and 10(64-bit) , or C:\Program Files (x86) in Windows XP(64-bit), Vista(64-bit), 7(64-bit), 8(64-bit), 8.1(64-bit), 2008(64-bit), 2012(64-bit) and 10(64-bit).)

Other System Modifications

This Backdoor adds the following registry entries:

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Run
Vyfw = "%AppDataLocal%\Vyfw\Vyfw.hta"

HKEY_CURRENT_USER\Environment
windir = "cmd /c start /min %Public%\x.bat reg delete hkcu\Environment /v windir /f && REM"

HKEY_CURRENT_USER\Software\Remcos-MCNA55
exepath = {hex values}

HKEY_CURRENT_USER\Software\Remcos-MCNA55
licence = {hex values}

Other Details

This Backdoor adds the following registry keys:

HKEY_CURRENT_USER\Software\Remcos-MCNA55

It connects to the following possibly malicious URL:

  • http://doc-0c-54-docs.{BLOCKED}usercontent.com

  SOLUTION

Minimum Scan Engine: 9.850
FIRST VSAPI PATTERN FILE: 15.862.08
FIRST VSAPI PATTERN DATE: 11 May 2020
VSAPI OPR PATTERN File: 15.863.00
VSAPI OPR PATTERN Date: 12 May 2020

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.XXPE50FFF035

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

Restart in Safe Mode

[ Learn More ]

Step 5

Delete this registry value

[ Learn More ]

Important: Editing the Windows Registry incorrectly can lead to irreversible system malfunction. Please do this step only if you know how or you can ask assistance from your system administrator. Else, check this Microsoft article first before modifying your computer's registry.

 
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Run
    • Vyfw = "%AppDataLocal%\Vyfw\Vyfw.hta"
  • In HKEY_CURRENT_USER\Environment
    • windir = "cmd /c start /min  %Public%\x.bat reg  delete hkcu\Environment /v windir /f && REM"
  • In HKEY_CURRENT_USER\Software\Remcos-MCNA55
    • exepath = {hex values}
  • In HKEY_CURRENT_USER\Software\Remcos-MCNA55
    • licence = {hex values}

Step 6

Delete this registry key

[ Learn More ]

Important: Editing the Windows Registry incorrectly can lead to irreversible system malfunction. Please do this step only if you know how or you can ask assistance from your system administrator. Else, check this Microsoft article first before modifying your computer's registry.

  • In HKEY_CURRENT_USER\Software\Remcos-MCNA55
    • (null)

Step 7

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.
  • %User Temp%\Cab{random numbers}.tmp
  • %User Temp%\Tar{random numbers.tmp
  • %AppDataLocal%\Vyfw\Vyfwset.exe
  • %AppDataLocal%\Vyfw\Vyfw.hta
  • %AppDataLocal%\Vyfw\Fuck
  • %Public%\x.bat
  • %Public%\Natso.bat
  • %Application Data%\remcos\logs.dat

Step 8

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.
  • %AppDataLocal%\Vyfw\
  • %Application Data%\remcos\

Step 9

Restart in normal mode and scan your computer with your Trend Micro product for files detected as Backdoor.Win32.REMCOS.USMANEAGGK. 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 this Knowledge Base page for more information.


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