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Worm.VBS.DUNIHI.YYSXU

February 06, 2020
 Analysis by: Joshua John Bantayan
 ALIASES:

VB:Trojan.Valyria.2826 (BITDEFENDER); Trojan-Dropper.VBS.Houdini (IKARUS)

 PLATFORM:

Windows

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

  • Threat Type: Worm

  • Destructiveness: No

  • Encrypted:

  • In the wild: Yes

  OVERVIEW


This Worm arrives on a system as a file dropped by other malware or as a file downloaded unknowingly by users when visiting malicious sites.

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

  TECHNICAL DETAILS

File Size:

229,406 bytes

File Type:

VBS

Initial Samples Received Date:

20 Jan 2020

Arrival Details

This Worm 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 Worm adds the following processes:

  • "%System%\wscript.exe" //B "%Application Data%\nXDLKezaVy.vbs"
  • "%System%\wscript.exe" //B "%Application Data%\{Malware Name}.vbs"

(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 Worm adds the following registry entries to enable its automatic execution at every system startup:

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Run
{Malware name} = “wscript.exe //B "%Application Data%\{Malware name}.vbs"”

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Run
nXDLKezaVy = “wscript.exe //B "%Application Data%\nXDLKezaVy.vbs"”

HKEY_LOCAL_MACHINE\Software\Microsoft\
Windows\CurrentVersion\Run
{Malware name} = “wscript.exe //B "%Application Data%\{Malware name}.vbs"”

HKEY_LOCAL_MACHINE\Software\Microsoft\
Windows\CurrentVersion\Run
nXDLKezaVy = “wscript.exe //B "%Application Data%\nXDLKezaVy.vbs"”

It drops the following file(s) in the Windows Common Startup folder to enable its automatic execution at every system startup:

  • %Common Startup%\{Malware Name}.vbs
  • %Common Startup%\nXDLKezaVy.vbs

(Note: %Common Startup% is the startup folder for all users, which is usually C:\Documents and Settings\All Users\Start Menu\Programs\Startup on Windows 2000, XP, and Server 2003, or C:\ProgramData\Microsoft\Windows\Start Menu\Programs\Startup on Windows Vista, 7, and 8.)

Propagation

This Worm creates shortcut files (.LNK) disguised as folders or files located on the affected drives pointing to the malware copy.

Dropping Routine

This Worm drops the following files:

  • %Application Data%\ nXDLKezaVy.vbs
  • %Application Data%\{Malware name}.vbs
  • {Removable Drive Letter}:\nXDLKezaVy.vbs

(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).)

Other Details

This Worm adds the following registry keys:

HKEY_LOCAL_MACHINE\SOFTWARE\{Malware name}
= - {Current machine date}

HKEY_LOCAL_MACHINE\SOFTWARE\nXDLKezaVy
= - {Current machine date}

It connects to the following URL(s) to get the affected system's IP address:

  • http://i{BLOCKED}.com

It connects to the following possibly malicious URL:

  • {BLOCKED}tl.com:4132
  • {BLOCKED}laipallets.com:5000

It does the following:

  • It hides files and folders located on affected removable drives.

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

  SOLUTION

Minimum Scan Engine:

9.850

FIRST VSAPI PATTERN FILE:

15.652.04

FIRST VSAPI PATTERN DATE:

30 Jan 2020

VSAPI OPR PATTERN File:

15.653.00

VSAPI OPR PATTERN Date:

31 Jan 2020

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

Restart in Safe Mode

[ Learn More ]

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
    • {Malware name} = “wscript.exe //B "%Application Data%\{Malware name}.vbs"”
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Run
    • nXDLKezaVy = “wscript.exe //B "%Application Data%\nXDLKezaVy.vbs"”
  • In HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Run
    • {Malware name} = “wscript.exe //B "%Application Data%\{Malware name}.vbs"”
  • In HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Run
    • nXDLKezaVy = “wscript.exe //B "%Application Data%\nXDLKezaVy.vbs"”

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.

  • In HKEY_LOCAL_MACHINE\SOFTWARE
    • {Malware name}
  • In HKEY_LOCAL_MACHINE\SOFTWARE
    • nXDLKezaVy

Step 6

Search and delete these files

[ 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%\ nXDLKezaVy.vbs
  • %Application Data%\{Malware name}.vbs
  • %Common Startup%\{Malware Name}.vbs
  • %Common Startup%\nXDLKezaVy.vbs
  • {Removable Drive Letter}:\nXDLKezaVy.vbs

Step 7

Restart in normal mode and scan your computer with your Trend Micro product for files detected as Worm.VBS.DUNIHI.YYSXU. 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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