WORM_VOBFUS.ZTN

 Analysis by: Jaime Benigno Reyes

 ALIASES:

Worm:Win32/Vobfus.NN (Microsoft), a variant of Win32/VBObfus.LP trojan (Nod32), Troj/Agent-AAOL (Sophos), Trojan horse VB2.KQC (AVG)

 PLATFORM:

Windows 2000, Windows Server 2003, Windows XP (32-bit, 64-bit), Windows Vista (32-bit, 64-bit), Windows 7 (32-bit, 64-bit)

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

  • Threat Type: Worm

  • Destructiveness: No

  • Encrypted:

  • In the wild: Yes

  OVERVIEW

This worm arrives by connecting affected removable drives to a system.

  TECHNICAL DETAILS

File Size:

286,720 bytes

File Type:

EXE

Memory Resident:

Yes

Initial Samples Received Date:

10 Mar 2013

Arrival Details

This worm arrives by connecting affected removable drives to a system.

Installation

This worm drops the following file(s)/component(s):

  • {removable drive letter}:\x.mpeg

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

  • %User Profile%\{random}.exe

(Note: %User Profile% is the current user's profile folder, which is usually C:\Documents and Settings\{user name} on Windows 2000, XP, and Server 2003, or C:\Users\{user name} on Windows Vista and 7.)

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
{random} = "%User Profile%\{random}.exe /{random letter}"

Other System Modifications

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

HKEY_LOCAL_MACHINE\SOFTWARE\Policies\
Microsoft\Windows\WindowsUpdate\
AU
NoAutoUpdate = "1"

It modifies the following registry entries to hide files with Hidden attributes:

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Explorer\
Advanced
ShowSuperHidden = "0"

(Note: The default value data of the said registry entry is "1".)

Propagation

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

  • {removable drive letter}:\{random file name}.exe
  • {removable drive letter}:\Passwords.exe
  • {removable drive letter}:\Porn.exe
  • {removable drive letter}:\Secret.exe
  • {removable drive letter}:\Sexy.exe
  • {removable drive letter}:\{folder name}.exe

The said .INF file contains the following strings:

{garbage characters}
[autorun]
{garbage characters}
open={random}.eXE
{garbage characters}
ACTION={random number}
{garbage characters}
UsEaUTopLay=1
{garbage characters}

Other Details

This worm connects to the following possibly malicious URL:

  • http://{BLOCKED}5.no-ip2.net:81
  • http://{BLOCKED}I.no-ip2.net:81
  • http://{BLOCKED}M.NO-IP2.NET:81
  • http://{BLOCKED}r.ru
  • http://{BLOCKED}g.su
  • http://{BLOCKED}s.su

NOTES:

This worm searches for folders in all removable drives then drops copies of itself as {folder name}.exe.

It also uses the file names of files with the following extensions:

  • .avi
  • .bmp
  • .doc
  • .gif
  • .jpe
  • .jpg
  • .mp3
  • .mp4
  • .mpg
  • .pdf
  • .png
  • .tif
  • .txt
  • .wav
  • .wma
  • .wmv
  • .xls

It then sets the attribute of the original file or folder to Hidden and System to trick users into thinking that the dropped copy is the legitimate file or folder.

  SOLUTION

Minimum Scan Engine:

9.300

FIRST VSAPI PATTERN FILE:

9.778.04

FIRST VSAPI PATTERN DATE:

10 Mar 2013

VSAPI OPR PATTERN File:

9.779.00

VSAPI OPR PATTERN Date:

11 Mar 2013

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

Scan your computer with your Trend Micro product and note files detected as WORM_VOBFUS.ZTN

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
    • {random} = "%User Profile%\{random}.exe /{random letter}"
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows\WindowsUpdate\AU
    • NoAutoUpdate = "1"

Step 5

Restore this modified 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\Explorer\Advanced
    • From: ShowSuperHidden = "0"
      To: ShowSuperHidden = "1"

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.
  • {removable drive letter}:\x.mpeg

Step 7

Search and delete AUTORUN.INF files created by WORM_VOBFUS.ZTN that contain these strings

[ Learn More ]
 
  • {garbage characters}
  • [autorun]
  • {garbage characters}
  • open={random}.eXE
  • {garbage characters}
  • ACTION={random number}
  • {garbage characters}
  • UsEaUTopLay=1
  • {garbage characters}

Step 8

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