Analysis by: Paul Steven Nadera

ALIASES:

HEUR:Trojan.Win32.RMS.gen (Kaspersky);

 PLATFORM:

Windows

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

  • Threat Type: Backdoor

  • Destructiveness: No

  • Encrypted: Yes

  • 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.

It connects to a website to send and receive information.

However, as of this writing, the said sites are inaccessible.

  TECHNICAL DETAILS

File Size: 6,058,495 bytes
File Type: EXE
Memory Resident: Yes
Initial Samples Received Date: 10 May 2021
Payload: Connects to URLs/IPs, Drops files, Steals information

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:

  • %Application Data%\WinRAR
  • %Application Data%\WinRAR\Version

(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).)

It drops the following files:

  • %Application Data%\WinRAR\Version\winspool.drv -> contains malicious routines
  • %Application Data%\WinRAR\Version\UniPrint.exe
  • %Application Data%\WinRAR\Version\WinPrint.exe -> loads winspool.drv
  • %Application Data%\WinRAR\Version\libeay32.dll
  • %Application Data%\WinRAR\Version\ssleay32.dll

(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).)

It adds the following processes:

  • "%Application Data%\WinRAR\Version\WinPrint.exe"
  • "%Application Data%\WinRAR\Version\UniPrint.exe"
  • "C:\Windows\System32\cmd.exe" /c REG ADD "HKEY_CURRENT_USER\SOFTWARE\Microsoft\Windows\CurrentVersion\RunOnce" /V "Virtual Printer Driver" /t REG_SZ /F /D "\"%Application Data%\WinRAR\Version\WinPrint.exe\""
  • REG ADD "HKEY_CURRENT_USER\SOFTWARE\Microsoft\Windows\CurrentVersion\RunOnce" /V "Virtual Printer Driver" /t REG_SZ /F /D "\"%Application Data%\WinRAR\Version\WinPrint.exe\""

(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\RunOnce
Virtual Printer Driver = "%Application Data%\WinRAR\Version\WinPrint.exe"

Other System Modifications

This Backdoor adds the following registry entries as part of its installation routine:

HKEY_CURRENT_USER\Software\WDMPrint
General = {Hex values}

HKEY_CURRENT_USER\Software\WDMPrint
Security = {Hex values}

HKEY_CURRENT_USER\Software\WDMPrint
InternetId = {Hex values}

HKEY_CURRENT_USER\Software\WDMPrint
Certificates = {Hex values}

Backdoor Routine

This Backdoor connects to the following websites to send and receive information:

  • raven-b.{BLOCKED}sting.com:5655
  • {BLOCKED}.{BLOCKED}.252.66:5655

Information Theft

This Backdoor gathers the following data:

  • Host name
  • Country code
  • Operating System
  • If it has admin privileges

Other Details

This Backdoor adds the following registry keys:

HKEY_CURRENT_USER\Software\WDMPrint

It connects to the following possibly malicious URL:

  • http://{BLOCKED}istries.com/templates/data/command.php?t=2&id={Unique ID}

It does the following:

  • Self extracting file containing the malicious file and its components
  • Backdoor commands are the same as the remote capabilities of HackTool.Win32.Radmin.GQ

However, as of this writing, the said sites are inaccessible.

  SOLUTION

Minimum Scan Engine: 9.800
FIRST VSAPI PATTERN FILE: 16.714.05
FIRST VSAPI PATTERN DATE: 12 May 2021
VSAPI OPR PATTERN File: 16.715.00
VSAPI OPR PATTERN Date: 13 May 2021

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

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 3

Identify and terminate files detected as Backdoor.Win32.RMSRAT.C

[ 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\RunOnce
    • Virtual Printer Driver = "%Application Data%\WinRAR\Version\WinPrint.exe"
  • In HKEY_CURRENT_USER\Software\WDMPrint
    • General ={Hex values}
  • In HKEY_CURRENT_USER\Software\WDMPrint
    • Security ={Hex values}
  • In HKEY_CURRENT_USER\Software\WDMPrint
    • InternetId = {Hex values}
  • In HKEY_CURRENT_USER\Software\WDMPrint
    • Certificates ={Hex values}

Step 5

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.

  • HKEY_CURRENT_USER\Software\WDMPrint

Step 6

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.
  • %Application Data%\WinRAR\Version\winspool.drv -> contains malicious routine
  • %Application Data%\WinRAR\Version\UniPrint.exe
  • %Application Data%\WinRAR\Version\WinPrint.exe -> loads winspool.drv
  • %Application Data%\WinRAR\Version\libeay32.dll
  • %Application Data%\WinRAR\Version\ssleay32.dll

Step 7

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%\WinRAR
  • %Application Data%\WinRAR\Version

Step 8

Scan your computer with your Trend Micro product to delete files detected as Backdoor.Win32.RMSRAT.C. 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:


Did this description help? Tell us how we did.