Analysis by: Michael Cabel
 PLATFORM:

Windows 98, ME, NT, 2000, XP, 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 removable drives

This worm may be dropped by other malware. It may be unknowingly downloaded by a user while visiting malicious websites.

It modifies registry entries to hide files with System and Read-only attributes.

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: 138,752 bytes
File Type: PE
Memory Resident: Yes
Initial Samples Received Date: 26 Jul 2010
Payload: Drops files

Arrival Details

This worm may be dropped by other malware.

It may be unknowingly downloaded by a user while visiting malicious websites.

Installation

This worm drops the following copies of itself into the affected system:

  • %User Profile%\{Random File Name}.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
{Malware File Name} = %User Profile%\{Random File Name}.exe

Other System Modifications

This worm modifies the following registry entries to hide files with System and Read-only 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 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:

[aUToRUN]
aCtioN=Open folder to view files
SHELLexeCUtE= {Random File Name}.eXE
ICOn=%sYsTEMRoOt%\SYSTEm32\sHelL32.DlL,4
USeAutoPLAy=1

Other Details

Based on analysis of the codes, it has the following capabilities:

  • This worm searches for folders on removable drives and create shortcut files on these drives using the folder names as its filename to execute its dropped copy. It then hides the folders found.
  • This worm also drops link files (.LNK files) with random file names in removable drives. The said .LNK file are detected by Trend Micro as LNK_STUXNET.SM. It also drops the file xxx.dll on removable drives detected by Trend Micro as WORM_VOBFUS.AI.

  SOLUTION

Minimum Scan Engine: 8.900
VSAPI PATTERN File: 7.339.80
VSAPI PATTERN Date: 26 Jul 2010
VSAPI PATTERN Date: 7/26/2010 12:00:00 AM

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

Remove the malware/grayware file dropped/downloaded by WORM_VBNA.SM

    LNK_STUXNET.SM
    WORM_VOBFUS.AI

Step 3

Terminate a process file/s detected as WORM_VBNA.SM

[ Learn More ]

*Note: If the detected file/s is/are not displayed in theWindows Task Manager, continue doing the next steps.

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
    • {Malware File Name} = %User Profile%\{Random File Name}.exe

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\CurrentVersion\Explorer\Advanced
    • From: ShowSuperHidden = 0
      To: ShowSuperHidden = 1

Step 6

Scan your computer with your Trend Micro product to delete files detected as WORM_VBNA.SM. 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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