Backdoor.Win32.REMCOS.FNTBL
HEUR:Backdoor.Win32.Remcos.gen (KASPERSKY)
Windows
![](/vinfo/imgFiles/legend.jpg)
Threat Type: Backdoor
Destructiveness: No
Encrypted: Yes
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
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:
- %User Temp%\Cab6D62.tmp
- %User Temp%\Tar6D63.tmp
- %AppDataLocal%\Puzv\Puzvset.exe
- %AppDataLocal%\Puzv\Puzv.hta
- %AppDataLocal%\Puzv\Muck
- %Public%\cde.bat
- %Public%\x.bat
- %Public%\x.vbs
- %Public%\Natso.bat
- %Application Data%\winos\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).)
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\RunOnce
Puzv = %AppDataLocal%\Puzv\Puzv.hta
Other System Modifications
This Backdoor adds the following registry entries:
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_{Random characters}
EXEpath =
Other Details
This Backdoor adds the following registry keys:
HKEY_CURRENT_USER\Software\remcos_{Random characters}
It connects to the following possibly malicious URL:
- http://doc-08-0s-docs.{BLOCKED}usercontent.com:443
SOLUTION
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
Step 5
Delete this registry value
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\RunOnce
- Puzv = %AppDataLocal%\Puzv\Puzv.hta
- Puzv = %AppDataLocal%\Puzv\Puzv.hta
- In HKEY_CURRENT_USER\Environment
- windir = cmd /c start /min %Public%\x.bat reg delete hkcu\Environment /v windir /f && REM
- windir = cmd /c start /min %Public%\x.bat reg delete hkcu\Environment /v windir /f && REM
Step 6
Delete this registry key
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. Before you could do this, you must restart in Safe Mode. For instructions on how to do this, you may refer to this page If the preceding step requires you to restart in safe mode, you may proceed to edit the system registry.
- In HKEY_CURRENT_USER\Software
- remcos_{Random characters}
- remcos_{Random characters}
Step 7
Search and delete these files
- %User Temp%\Cab6D62.tmp
- %User Temp%\Tar6D63.tmp
- %AppDataLocal%\Puzv\Puzvset.exe
- %AppDataLocal%\Puzv\Puzv.hta
- %AppDataLocal%\Puzv\Muck
- %Public%\cde.bat
- %Public%\x.bat
- %Public%\x.vbs
- %Public%\Natso.bat
- %Application Data%\winos\logs.dat
Step 8
Restart in normal mode and scan your computer with your Trend Micro product for files detected as Backdoor.Win32.REMCOS.FNTBL. 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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