WORM_VOBFUS.SM0

 Analysis by: Karl Dominguez

 ALIASES:

W32.Changeup!gen10 (Symantec); Worm:Win32/Vobfus.gen!F (Microsoft); VBObfus.n (Mcafee); Mal/SillyFDC-M (Sophos)

 PLATFORM:

Windows 2000, Windows XP, Windows Server 2003

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

  • Threat Type: Worm

  • Destructiveness: No

  • Encrypted: Yes

  • In the wild: Yes

  OVERVIEW

Infection Channel:

Propagates via removable drives

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.

It drops copies of itself in all removable drives. It drops an AUTORUN.INF file to automatically execute the copies it drops when a user accesses the drives of an affected system.

  TECHNICAL DETAILS

File Size:

253,952 bytes

File Type:

EXE

Memory Resident:

Yes

Initial Samples Received Date:

22 Apr 2011

Payload:

Compromises system security, Downloads files

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:

  • %User Profile%\{random filename}.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 filename} = %User Profile%\{random filename}.exe

Other System Modifications

This worm modifies the following registry entries:

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 copies of itself in all removable drives.

It drops an AUTORUN.INF file to automatically execute the copies it drops when a user accesses the drives of an affected system.

The said .INF file contains the following strings:

{garbage characters}
[autorun]
{garbage characters}
open={random filename}.eXE
{garbage characters}
iCon={random filename}.ico
{garbage characters}
USeaUToplaY=1
{garbage characters}

Backdoor Routine

This worm opens the following port(s) where it listens for remote commands:

  • 8000

It connects to the following URL(s) to send and receive commands from a remote malicious user:

  • server.{BLOCKED}et.com

Other Details

This worm attempts to access the following websites to download files, which are possibly malicious:

  • {BLOCKED}eoall.net
  • {BLOCKED}iashares.org
  • {BLOCKED}yer1253.com

NOTES:

This malware drops .LNK files in removable drives that point to a copy of itself. This is done to trick users into clicking the shorcut files and execute the malware copy. These .LNK files use the following file names:

  • Documents.lnk
  • Music.lnk
  • New Folder.lnk
  • Passwords.lnk
  • Pictures.lnk
  • Video.lnk

It also uses the names of existing folders and names of files with the following extensions:

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

This routine enables the copy of the worm to execute first before opening the real folder or file. It then changes the attributes of the original folders and files to Hidden and System to avoid early detection. It also adds the following non-malicious component files in removable drives:

  • {random filename}.ico
  • x.mpeg

  SOLUTION

Minimum Scan Engine:

8.900

VSAPI OPR PATTERN File:

8.113.00

VSAPI OPR PATTERN Date:

23 Apr 2011

Step 1

For Windows XP and Windows Server 2003 users, before doing any scans, please make sure you disable System Restore to allow full scanning of your computer.

Step 2

Identify and terminate files detected as WORM_VOBFUS.SM0

[ Learn More ]
  1. Windows Task Manager may not display all running processes. In this case, please use a third-party process viewer, preferably Process Explorer, to terminate the malware/grayware/spyware file. You may download the said tool here.
  2. If the detected file is displayed in either Windows Task Manager or Process Explorer but you cannot delete it, restart your computer in safe mode. To do this, refer to this link for the complete steps.
  3. If the detected file is not displayed in either Windows Task Manager or Process Explorer, continue doing the next steps.

Step 3

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 filename} = %User Profile%\{random filename}.exe

Step 4

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: 1

Step 5

Search and delete AUTORUN.INF files created by WORM_VOBFUS.SM0 that contain these strings

[ Learn More ]
{garbage characters}
[autorun]
{garbage characters}
open={random filename}.eXE
{garbage characters}
iCon={random filename}.ico
{garbage characters}
USeaUToplaY=1
{garbage characters}

Step 6

Search and delete this file

[ Learn More ]
There may be some component 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.
Documents.lnk
Music.lnk
New Folder.lnk
Passwords.lnk
Pictures.lnk
Video.lnk
{random filename}.ico
x.mpeg

Step 7

Scan your computer with your Trend Micro product to delete files detected as WORM_VOBFUS.SM0. 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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