Analysis by: John Kevin Sanchez
ALIASES:

Worm:Win32/Conustr.A (Microsoft), Worm.Win32.Conustr (Ikarus), Trojan.Win32.Vague.bn (Kaspersky)

 PLATFORM:

Windows

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

  • Threat Type: Worm

  • Destructiveness: No

  • Encrypted: No

  • In the wild: Yes

  OVERVIEW

Infection Channel: Downloaded from the Internet, Dropped by other malware

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.

  TECHNICAL DETAILS

File Size: 139,264 bytes
File Type: EXE
Memory Resident: Yes
Initial Samples Received Date: 17 Oct 2016
Payload: Creates files, Modifies system registry, Steals information

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 drops the following copies of itself into the affected system and executes them:

  • %User Temp%\conhost.exe

(Note: %User Temp% is the user's temporary folder, where it usually is C:\Documents and Settings\{user name}\Local Settings\Temp on Windows 2000, Windows Server 2003, and Windows XP (32- and 64-bit); C:\Users\{user name}\AppData\Local\Temp 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.)

It creates the following folders:

  • %User Temp%\WPDNSE
  • {Removable Drive Letter}:\RECYCLER

(Note: %User Temp% is the user's temporary folder, where it usually is C:\Documents and Settings\{user name}\Local Settings\Temp on Windows 2000, Windows Server 2003, and Windows XP (32- and 64-bit); C:\Users\{user name}\AppData\Local\Temp 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.)

Other System Modifications

This worm adds the following registry entries:

HKEY_LOCAL_MACHINE\SOFTWARE\Classes\
exefile
NeverShowExt = ""

It modifies the following registry entries:

HKEY_CURRENT_USER\Software\Microsoft\
Windows NT\CurrentVersion\Windows
Load = "%User Temp%\conhost.exe"

(Note: The default value data of the said registry entry is "".)

Propagation

This worm drops the following copies of itself in all physical and removable drives:

  • {Removable Drive Letter}:\{Folder Name}.exe

Dropping Routine

This worm drops the following files:

  • %User Temp%\ppxxxx
  • %User Temp%\winword4.doc - contains stolen information
  • %User Temp%\must.bat
  • {Removable Drive Letter}:\RECYCLER\{random filename}.NLS - password protected archive file containing %User Temp%\winword4.doc
  • %User Temp%\WPDNSE\{random filename}.NLS - password protected archive file containing %User Temp%\winword4.doc

(Note: %User Temp% is the user's temporary folder, where it usually is C:\Documents and Settings\{user name}\Local Settings\Temp on Windows 2000, Windows Server 2003, and Windows XP (32- and 64-bit); C:\Users\{user name}\AppData\Local\Temp 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.)

Information Theft

This worm gathers the following data:

  • OS version
  • Network Information
  • System Information
  • Running Processes
  • Running Services
  • List of files and directories of drives C:\, D:\, E:\, F:\, G:\, H:\, I:\

NOTES:

The malware hides the folders in the removable drives.

The malware uses a folder icon to disguise itself.

  SOLUTION

Minimum Scan Engine: 9.750
FIRST VSAPI PATTERN FILE: 12.842.04
FIRST VSAPI PATTERN DATE: 17 Oct 2016
VSAPI OPR PATTERN File: 12.843.00
VSAPI OPR PATTERN Date: 18 Oct 2016

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

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_LOCAL_MACHINE\SOFTWARE\Classes\exefile
    • NeverShowExt = ""

Step 5

Restore these modified registry values

[ Learn More ]

Important:Editing the Windows Registry incorrectly can lead to irreversible system malfunction. Please do this only if you know how to or you can seek your system administrator's help. You may also check out this Microsoft article first before modifying your computer's registry.

  • In HKEY_CURRENT_USER\Software\Microsoft\Windows NT\CurrentVersion\Windows
    • From: Load = "%User Temp%\conhost.exe"
      To: Load = ""

Step 6

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.
  • %User Temp%\WPDNSE
  • {Removable Drive Letter}:\RECYCLER

Step 7

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.
  • {Removable Drive Letter}:\RECYCLER\{random filename}.NLS
  • %User Temp%\WPDNSE\{random filename}.NLS
  • %User Temp%\ppxxxx
  • %User Temp%\winword4.doc
  • %User Temp%\must.bat

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 WORM_CONUSTR.T. 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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