Analysis by: Jon Dexter Laurin

ALIASES:

Worm:VBS/Jenxcus (Microsoft); Trojan.VBS.Crypt.l (Kaspersky); Trojan.VBS.Crypt (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 via removable drives. It 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: 69,585 bytes
File Type: VBS
Memory Resident: Yes
Initial Samples Received Date: 25 Jun 2015

Arrival Details

This worm arrives via removable drives.

It 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 drops the following copies of itself into the affected system:

  • %Application Data%\{Malware Filename}.vbs
  • %User Startup%\{Malware Filename}.vbs

(Note: %Application Data% is the Application Data folder, where it usually is C:\Documents and Settings\{user name}\Application Data on Windows 2000, Windows Server 2003, and Windows XP (32- and 64-bit); C:\Users\{user name}\AppData\Roaming on Windows Vista (32- and 64-bit), Windows 7 (32- and 64-bit), Windows 8 (32- and 64-bit), Windows 8.1 (32- and 64-bit), Windows Server 2008, and Windows Server 2012.. %User Startup% is the current user's Startup folder, which is usually C:\Windows\Profiles\{user name}\Start Menu\Programs\Startup on Windows 98 and ME, C:\WINNT\Profiles\{user name}\Start Menu\Programs\Startup on Windows NT, and C:\Documents and Settings\{User name}\Start Menu\Programs\Startup.)

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 Filename} = "wscript.exe //B "%Application Data%\{Malware Filename}.vbs""

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

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

  • %User Startup%\{Malware Filename}.vbs

(Note: %User Startup% is the current user's Startup folder, which is usually C:\Windows\Profiles\{user name}\Start Menu\Programs\Startup on Windows 98 and ME, C:\WINNT\Profiles\{user name}\Start Menu\Programs\Startup on Windows NT, and C:\Documents and Settings\{User name}\Start Menu\Programs\Startup.)

Other System Modifications

This worm also creates the following registry entry(ies) as part of its installation routine:

HKEY_LOCAL_MACHINE\SOFTWARE\{Malware Filename}
(Default) = "{"true" or "false"} - {Installation Date}"

Propagation

This worm drops the following copy(ies) of itself in all removable drives:

  • {Removable Drive Letter}:\{Malware Filename}.vbs

Other Details

This worm connects to the following possibly malicious URL:

  • http://{BLOCKED}us.{BLOCKED}ee.com:991/is-ready
  • http://{BLOCKED}us.{BLOCKED}e.com:991/is-sending
  • http://{BLOCKED}us.{BLOCKED}e.com:991/is-recving

NOTES:

It drops .LNK files whose names correspond to the files and folders in the root directory of the removable drives. When the .LNK files are executed, the dropped copy of the malware on the drives is executed.

  SOLUTION

Minimum Scan Engine: 9.750
FIRST VSAPI PATTERN FILE: 11.752.04
FIRST VSAPI PATTERN DATE: 25 Jun 2015
VSAPI OPR PATTERN File: 11.753.00
VSAPI OPR PATTERN Date: 26 Jun 2015

Step 1

Before doing any scans, Windows XP, Windows Vista, and Windows 7 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

Scan your computer with your Trend Micro product and note files detected as VBS_DUNIHI.BT

Step 4

Restart in Safe Mode

[ Learn More ]

Step 5

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 Filename} = "wscript.exe //B "%Application Data%\{Malware Filename}.vbs""
  • In HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Run
    • {Malware Filename} = "wscript.exe //B "%Application Data%\{Malware Filename}.vbs""

Step 6

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\SOFTWARE
    • {Malware Filename}

Step 7

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%\{Malware Filename}.vbs
  • %User Startup%\{Malware Filename}.vbs
  • {Removable Drive Letter}:\{Malware Filename}.vbs
  • {Removable Drive Letter}:\{User File or Folder Names}.lnk
    

Step 8

  1. Open a command prompt.
    • For Windows 2000, Windows XP, and Windows Server 2003 users, click Start>Run. In the Search box, type CMD then press Enter.
    • For Windows Vista, Windows 7, and Windows Server 2008 users, click Start, type CMD in the Search input field then press Enter.
    • For Windows 8, Windows 8.1, and Windows Server 2012 users, right-click on the lower-left corner of the screen, click Command Prompt.
  2. In the CMD console, type the following:

    ATTRIB [+R | -R] [+A | -A ] [+S | -S] [+H | -H] [+I | -I] [drive:][path][file name] [/S [/D] [/L]]

    Where:
    + Sets an attribute.
    - Clears an attribute
    R Read-only file attribute
    A Archive file attribute
    S System file attribute
    H Hidden file attribute
    I Not content indexed file attribute
    [drive:][path][filename]
    Specifies a file or files for attrib to process
    /S Processes matching files in the current folder and all subfolders.
    /D Processes folders
    /L Work on the attributes of the Symbolic Link versus the target of the Symbolic Link
    Example:
    To unhide all files and folders (including subfolders) in drive D:
    ATTRIB –H D:\* /S /D
  3. Repeat Step 3 for folders and files in other drives or folders.

Step 9

Restart in normal mode and scan your computer with your Trend Micro product for files detected as VBS_DUNIHI.BT. 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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