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Backdoor.MSIL.REMCOS.AOQ

January 21, 2020
 ALIASES:

VirTool:MSIL/Lore.AD!MTB [non_writable_container], VirTool:MSIL/Lore.AD!MTB [non_writable_container] (Microsoft); GenericRXJE-SJ!4FFC197CA7CD (McAfee); HEUR:Trojan.MSIL.NanoBot.gen (Kaspersky); Trojan.Win32.Generic!BT (Sunbelt)

 PLATFORM:

Windows

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

  • 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:

444,416 bytes

File Type:

EXE

Memory Resident:

Yes

Initial Samples Received Date:

21 Jan 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 processes:

  • schtasks.exe /Create /TN "Updates\tbTwnJahFuSe" /XML "%User Temp%\tmpDC98.tmp"
  • "{malware file path and name}"
  • "%System%\WScript.exe" "%User Temp%\install.vbs"
  • %User Temp%\install.vbs

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

It creates the following folders:

  • %Application Data%\firefox

(Note: %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).)

Autostart Technique

This Backdoor adds the following registry entries to enable its automatic execution at every system startup:

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Run
firefox = "%Application Data%\firefox\firefox1.exe"

Other System Modifications

This Backdoor adds the following registry entries:

HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\
Microsoft\Windows NT\CurrentVersion\
Winlogon
Userinit = "%System%\userinit.exe, %Application Data%\firefox\firefox1.exe"

Dropping Routine

This Backdoor drops the following files:

  • %User Temp%\install.vbs
  • %Application Data%\firefox\firefox1.exe
  • %Application Data%\tbTwnJahFuSe.exe

(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).. %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).)

This report is generated via an automated analysis system.

  SOLUTION

Minimum Scan Engine:

9.850

Step 1

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 2

Restart in Safe Mode

[ Learn More ]

Step 3

Identify and terminate files detected as Backdoor.MSIL.REMCOS.AOQ

[ 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 4

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
    • firefox = "%Application Data%\firefox\firefox1.exe"
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Microsoft\Windows NT\CurrentVersion\Winlogon
    • Userinit = "%System%\userinit.exe, %Application Data%\firefox\firefox1.exe"

Step 5

Search and delete these components

[ Learn More ]
There may be some components 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%\install.vbs
  • %Application Data%\firefox\firefox1.exe
  • %Application Data%\tbTwnJahFuSe.exe

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.
  • %Application Data%\firefox

Step 7

Restart in normal mode and scan your computer with your Trend Micro product for files detected as Backdoor.MSIL.REMCOS.AOQ. 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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