VBS_AUTORUN.SMH

October 09, 2012
 Analysis by: Sabrina Lei Sioting
 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

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

1,793,672 bytes

File Type:

VBS

Initial Samples Received Date:

10 Feb 2012

Arrival Details

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

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:

  • %Windows%\Thumbs.vbs

(Note: %Windows% is the Windows folder, which is usually C:\Windows or C:\WINNT.)

Autostart Technique

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

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\CurrentVersion\Run
avctrl = "wscript.exe %Windows%\Thumbs.vbs"

Other System Modifications

This worm modifies the following registry key(s)/entry(ies) as part of its installation routine:

HKEY_CLASSES_ROOT\VBSFile
{default} = "Configuration Script"

(Note: The default value data of the said registry entry is VBScript Script File.)

HKEY_LOCAL_MACHINE\SOFTWARE\Classes\
VBSFileHKEY_LOCAL_MACHINE\SOFTWARE\Classes\
VBSFile
{default} = "Configuration Script"

(Note: The default value data of the said registry entry is VBScript Script File.)

Propagation

This worm drops the following copy of itself in all physical and removable drives:

  • Thumbs.vbs

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]
open=wscript.exe Thumbs.vbs
icon=0
shell\install = &Install
shell\install\command = wscript.exe Thumbs.vbs
shell\uninstall = &UnInstall
shell\uninstall\command = wscript.exe Thumbs.vbs
shell\readme = &Read Me
shell\readme\command = wscript.exe Thumbs.vbs
shell\help = &Help
shell\help\command = wscript.exe Thumbs.vbs
shell\Open = &Open
shell\Open\command = wscript.exe Thumbs.vbs
shell\Open\Default=1
shell\Run = &Run
shell\Run\command = wscript.exe Thumbs.vbs
shell\Run\Default=1
shell\explore=Explorer
shell\explore\Command=Explorer.exe

  SOLUTION

Minimum Scan Engine:

9.200

FIRST VSAPI PATTERN FILE:

8.768.01

FIRST VSAPI PATTERN DATE:

10 Feb 2012

VSAPI OPR PATTERN File:

8.769.00

VSAPI OPR PATTERN Date:

11 Feb 2012

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

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
    • avctrl = "wscript.exe %Windows%\Thumbs.vbs"

Step 3

Restore this modified registry value

[ 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_CLASSES_ROOT\VBSFile
    • From: {default} = "Configuration Script"
      To: {default} = "VBScript Script File"
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Classes\VBSFile
    • From: {default} = "Configuration Script"
      To: {default} = "VBScript Script File"

Step 4

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

[ Learn More ]
 [AUTORUN]
open=wscript.exe Thumbs.vbs
icon=0
shell\install = &Install
shell\install\command = wscript.exe Thumbs.vbs
shell\uninstall = &UnInstall
shell\uninstall\command = wscript.exe Thumbs.vbs
shell\readme = &Read Me
shell\readme\command = wscript.exe Thumbs.vbs
shell\help = &Help
shell\help\command = wscript.exe Thumbs.vbs
shell\Open = &Open
shell\Open\command = wscript.exe Thumbs.vbs
shell\Open\Default=1
shell\Run = &Run
shell\Run\command = wscript.exe Thumbs.vbs
shell\Run\Default=1
shell\explore=Explorer
shell\explore\Command=Explorer.exe

Step 5

Scan your computer with your Trend Micro product to delete files detected as VBS_AUTORUN.SMH. 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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