Analysis by: Cris Nowell Pantanilla
 PLATFORM:

Windows 2000, Windows XP, Windows Server 2003

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

  • Threat Type: Trojan

  • Destructiveness: No

  • Encrypted:

  • In the wild: Yes

  OVERVIEW

This Trojan 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 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: 8,432 bytes
Memory Resident: Yes
Initial Samples Received Date: 13 Jan 2009

Arrival Details

This Trojan 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.

Autostart Technique

This Trojan adds the following registry entries to enable its automatic execution at every system startup:

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Run
Explorer = "Wscript.exe //e:VBScript "%My Documents%\database.mdb"

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\CurrentVersion\Run
WinUpdate = "Wscript.exe //e:VBScript "%Windows%\:Microsoft Office Update for Windows XP.sys"

Other System Modifications

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

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Policies\
System
DisableRegistrytools = "1"

Propagation

This Trojan 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]
open=WScript.exe //e:VBScript thumb.db auto
shell\open=Open
shell\open\Command=WScript.exe //e:VBScript thumb.db auto
shell\open\Default=1
shell\explore=Explore
shell\explore\Command=WScript.exe //e:VBScript thumb.db auto

  SOLUTION

Minimum Scan Engine: 9.200
FIRST VSAPI PATTERN FILE: 5.764.07
FIRST VSAPI PATTERN DATE: 13 Jan 2009
VSAPI OPR PATTERN File: 5.765.00
VSAPI OPR PATTERN Date: 13 Jan 2009

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

Restart in Safe Mode

[ Learn More ]

Step 3

Enable Registry Editor

[ Learn More ]
By doing this step, you also enable other applications/programs disabled by this malware/grayware/spyware.

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\Microsoft\Windows\CurrentVersion\Run
    • WinUpdate = "Wscript.exe //e:VBScript %Windows%\:Microsoft Office Update for Windows XP.sys"
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Run
    • Explorer = "Wscript.exe //e:VBScript %My Documents%\database.mdb"

Step 5

Search and delete AUTORUN.INF files created by VBS_AUTORUN.BKL that contain these strings

[ Learn More ]

[autorun]
open=WScript.exe //e:VBScript thumb.db auto
shell\open=Open
shell\open\Command=WScript.exe //e:VBScript thumb.db auto
shell\open\Default=1
shell\explore=Explore
shell\explore\Command=WScript.exe //e:VBScript thumb.db auto

Step 6

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