Analysis by: Francesca Villasanta
ALIASES:

VHO:Backdoor.MSIL.Agent.gen (KASPERSKY); Trojan:MSIL/Marsilia.NA!MTB (MICROSOFT)

 PLATFORM:

Windows

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

  • Threat Type: Trojan

  • Destructiveness: No

  • Encrypted: No

  • In the wild: Yes

  OVERVIEW

This Trojan 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: 11,776 bytes
Memory Resident: Yes
Initial Samples Received Date: 31 Jan 2024
Payload: Drops files, Creates files, Modifies system registry

Arrival Details

This Trojan 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 Trojan drops the following files:

  • %Windows%\Help\Stage3.exe
  • {Malware Path}\log\Stage2{yyyy-MM-dd}.bin

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

It adds the following processes:

  • If the machine is not in Safe Mode and neither "%Windows%\Help\Finish.exe" nor "%Windows%\Help\Exclude.exe" exists:
    • "cmd" /c start %Windows%\Help\Stage3.exe
  • If the machine is in SafeMode but either "%Windows%\Help\Finish.exe" or "%Windows%\Help\Exclude.exe" exists:
    • "cmd" /c del %Windows%\Help\Stage3.exe
    • "cmd" /c del %Windows%\Help\Pay.txt
    • "sc" delete MSOfficeRunOncelsls
    • "reg" delete "HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\SafeBoot\Network\MSOfficeRunOncelsls" /f
    • "cmd" /c start ping 127.0.0.1 -n 10 && cmd /c del %Windows%\Help\Stage2.exe && cmd /c shutdown -r -f -t 00
    • "shutdown" -r -f -t 00
  • If the machine is not in Safe Mode and neither "%Windows%\Help\Finish.exe" nor "%Windows%\Help\Exclude.exe" exists:
    • "sc" create MSOfficeRunOncelsls binpath= %Windows%\Help\Stage2.exe start= auto displayname= MSOfficeRunOncelsls
    • "reg" add "HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\SafeBoot\Network\MSOfficeRunOncelsls" /t REG_SZ /d Service /f
    • "shutdown" -r -f -t 00

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

It creates the following folders:

  • {Malware Path}\log

Other System Modifications

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

HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\
Control\SafeBoot\Network\
MSOfficeRunOncelsls
(default) = Service

It adds the following registry keys as part of its installation routine:

HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\
Control\SafeBoot\Network\
MSOfficeRunOncelsls

It deletes the following registry keys:

HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\
Control\SafeBoot\Network\
MSOfficeRunOncelsls

Other Details

This Trojan does the following:

  • It configures the Boot Configuration Data (BCD) to:
    • enable safe boot option with networking
    • disable safe boot option
  • It checks for the following files to determine prior compromise or the exclusion of the machine from infection:
    • %Windows%\Help\Finish.exe
    • %Windows%\Help\Exclude.exe
  • It creates a log file if any error is encountered during execution.
  • It performs different actions depending on the result of system and file checks:
    • If executed in Safe Mode and passed the file verification:
      • It decrypts the contents of the file %Windows%\Help\Pay.txt using a hard-coded decryption key.
      • The decrypted content is saved as %Windows%\Help\Stage3.exe and executed.
    • If executed in Safe Mode but did not pass the file verification:
      • It disables the Safe Boot option, deletes malware remnants, and reboots the machine.
    • If not executed in Safe Mode and passed the file verification:
      • It enables the Safe Boot with Networking, creates a service, adds a registry key, and reboots the machine.
  • It adds the following service:
    • Name: MSOfficeRunOncelsls
    • Start Type: Autostart
    • Binary Path: %Windows%\Help\Stage2.exe
  • It deletes the following service:
    • MSOfficeRunOncelsls

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

It deletes the following files to remove its traces in the system:

  • %Windows%\Help\Stage3.exe
  • %Windows%\Help\Pay.txt
  • %Windows%\Help\Stage2.exe

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

  SOLUTION

Minimum Scan Engine: 9.800
FIRST VSAPI PATTERN FILE: 19.144.04
FIRST VSAPI PATTERN DATE: 07 Feb 2024
VSAPI OPR PATTERN File: 19.145.00
VSAPI OPR PATTERN Date: 08 Feb 2024

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:

    Ransom.Win32.TRX.XXPE50FFF077

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

Disable this malware service

[ Learn More ]
  •  
    • MSOfficeRunOncelsls

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. 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.

  • HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\Control\SafeBoot\Network\MSOfficeRunOncelsls

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.
  • %Windows%\Help\Stage3.exe
  • {Malware Path}\log\Stage2{yyyy-MM-dd}.bin

Step 7

Search and delete these folders

[ 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.  
  • {Malware Path}\log

Step 8

Scan your computer with your Trend Micro product to delete files detected as Trojan.MSIL.RAWLD.THBOFBD. 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:


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