Analysis by: Carlos Villegas Madrid
ALIASES:

UDS:Trojan-Spy.MSIL.Solmyr.gen (KASPERSKY)

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

  TECHNICAL DETAILS

File Size: 3,992,576 bytes
File Type: EXE
Memory Resident: Yes
Initial Samples Received Date: 31 Mar 2023
Payload: Connects to URLs/IPs, Collects system information, Modifies system registry

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%\wbnh

(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%\wbnh\wbnh.exe
  • %User Profile%\appData\Local:{Current Date}

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

It adds the following processes:

  • "{Malware Path}\{Malware File Name}.exe"
  • "cmd" /c mkdir "%Application Data%\wbnh"
  • "cmd" /c schtasks /create /sc minute /mo 1 /tn "Nafifas" /tr "'%Application Data%\wbnh\wbnh.exe'" /f
  • "cmd" /c copy "{Malware Path}\{Malware File Name}.exe" "%Application Data%\wbnh\wbnh.exe"
  • schtasks /create /sc minute /mo 1 /tn "Nafifas" /tr "'%Application Data%\wbnh\wbnh.exe'" /f

(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).)

Backdoor Routine

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

  • Download and execute file
  • Execute malicious code in to the memory
  • Execute XMR miner
  • Access webcam & microphone
  • Manage Files (Delete, Compress, Search)

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

  • {BLOCKED}.{BLOCKED}.28.92:3569

Information Theft

This Backdoor gathers the following data:

  • System Information
  • Product Information
  • Clipboard Data
  • Keyboard Input

Other Details

This Backdoor adds the following registry keys:

HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\
Control\MediaResources

HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\
Control\MediaResources\msvideo

HKEY_LOCAL_MACHINE\SOFTWaRE\Microsoft\
DownloadManager

It does the following:

  • It creates the following scheduled task:
    • Name: Nafifas
    • Trigger: After triggered, repeat every 00:01:00 indefinitely
    • Action: %Application Data%\wbnh\wbnh.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).)

It accepts the following parameters:

  • -fwa
  • -tsc
  • -prs → Establish persistency
  • -uac → Privilege escalation
  • -wdkill → Disables Windows Defender

  SOLUTION

Minimum Scan Engine: 9.800
FIRST VSAPI PATTERN FILE: 18.396.04
FIRST VSAPI PATTERN DATE: 20 Apr 2023
VSAPI OPR PATTERN File: 18.397.00
VSAPI OPR PATTERN Date: 21 Apr 2023

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.XXPE50FFF067

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

Identify and terminate files detected as Backdoor.MSIL.SOLMYR.B

[ 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 6

Deleting Scheduled Tasks

The following {Task Name} - {Task to be run} listed should be used in the steps identified below:

  • Task Name: Nafifas
  • Task to be run: %Application Data%\wbnh\wbnh.exe

For Windows 2000, Windows XP, and Windows Server 2003:

  1. Open the Windows Scheduled Tasks. Click Start>Programs>Accessories>
    System Tools>Scheduled Tasks.
  2. Locate each {Task Name} values listed above in the Name column.
  3. Right-click on the said file(s) with the aforementioned value.
  4. Click on Properties. In the Run field, check for the listed {Task to be run}.
  5. If the strings match the list above, delete the task.

For Windows Vista, Windows 7, Windows Server 2008, Windows 8, Windows 8.1, and Windows Server 2012:

  1. Open the Windows Task Scheduler. To do this:
    • On Windows Vista, Windows 7, and Windows Server 2008, click Start, type taskschd.msc in the Search input field, then press Enter.
    • On Windows 8, Windows 8.1, and Windows Server 2012, right-click on the lower left corner of the screen, click Run, type taskschd.msc, then press Enter.
  2. In the left panel, click Task Scheduler Library.
  3. In the upper-middle panel, locate each {Task Name} values listed above in the Name column.
  4. In the lower-middle panel, click the Actions tab. In the Details column, check for the {Task to be run} string.
  5. If the said string is found, delete the task.

Step 7

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_LOCAL_MACHINE\SYSTEM\ControlSet001\Control\MediaResources\msvideo
  • In HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\Control\MediaResources
  • In HKEY_LOCAL_MACHINE\SOFTWaRE\Microsoft\DownloadManager

Step 8

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%\wbnh\wbnh.exe
  • %User Profile%\appData\Local:{Current Date}

Step 9

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%\wbnh

Step 10

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