Analysis by: Sabrina Lei Sioting

ALIASES:

W32.Changeup (Symantec_Beta); Worm:Win32/Vobfus.gen!F (Microsoft); VBObfus.g (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: No

  • In the wild: Yes

  OVERVIEW

Infection Channel: Propagates via flashdrives

This malware drops .LNK files in removable drives that point to a copy of itself. This is done to automatically execute dropped copies when the said drives are accessed. These .LNK files use certain file names. It also uses the names of existing folders and names of files with certain extensions. 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 certain non-malicious files in 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: 233,472 bytes
File Type: PE
Memory Resident: Yes
Initial Samples Received Date: 18 Mar 2011
Payload: Drops files, 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:

  • {BLOCKED}r.{BLOCKED}et.com

Other Details

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

  • {BLOCKED}1.player1253.com
  • {BLOCKED}1.videoall.net
  • {BLOCKED}1.mediashares.org

NOTES:
This malware drops .LNK files in removable drives that point to a copy of itself. This is done to automatically execute dropped copies when the said drives are accessed. 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
  • .jpeg
  • .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 files in removable drives:
  • {random filename}.icox.mpeg

  SOLUTION

Minimum Scan Engine: 8.900
FIRST VSAPI PATTERN FILE: 7.910.18
FIRST VSAPI PATTERN DATE: 19 Mar 2011
VSAPI OPR PATTERN File: 7.913.00
VSAPI OPR PATTERN Date: 20 Mar 2011

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.SMEP

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

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: 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. {random filename}.ico
x.mpeg

Step 7

Search and delete AUTORUN.INF files created by WORM_VOBFUS.SMEP 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 8

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


Did this description help? Tell us how we did.