VBS_AUTORUN.IHT

June 26, 2014
 Analysis by: Vincent Martin Hermosura
 ALIASES:

Troj/VBS-CC (Sophos), Trojan.VBS.Autorun.v (Kaspersky), Worm:VBS/Autorun.BT (Microsoft), VBS/Autorun.worm.aadz (NAI), Trojan.Malscript (Norton), VBS/Autorunner.C (Antivir)

 PLATFORM:

Windows 2000, Windows Server 2003, Windows XP (32-bit, 64-bit), Windows Vista (32-bit, 64-bit), Windows 7 (32-bit, 64-bit)

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

  • Threat Type: Worm

  • Destructiveness: No

  • Encrypted:

  • In the wild: Yes

  OVERVIEW

This worm 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:

184,508 bytes

File Type:

VBS

Initial Samples Received Date:

10 May 2013

Arrival Details

This worm 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:

  • %Program Files%\Common Files\System\Windows Update\wxz.dat
  • %Application Data%\Microsoft\SYSTEM\cste

(Note: %Program Files% is the default Program Files folder, usually C:\Program Files in Windows 2000, Server 2003, and XP (32-bit), Vista (32-bit), and 7 (32-bit), or C:\Program Files (x86) in Windows XP (64-bit), Vista (64-bit), and 7 (64-bit).. %Application Data% is the current user's Application Data folder, which is usually C:\Documents and Settings\{user name}\Application Data on Windows 2000, XP, and Server 2003, or C:\Users\{user name}\AppData\Roaming on Windows Vista and 7.)

It creates the following folders:

  • %Program Files%\Common Files\System\Windows Update

(Note: %Program Files% is the default Program Files folder, usually C:\Program Files in Windows 2000, Server 2003, and XP (32-bit), Vista (32-bit), and 7 (32-bit), or C:\Program Files (x86) in Windows XP (64-bit), Vista (64-bit), and 7 (64-bit).)

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\policies\
Explorer\Run
Updates = "%Windows%\svchost .exe" /e:VBScript.Encode "%Application Data%\Microsoft\SYSTEM\cste"""

Other System Modifications

This worm adds the following registry entries:

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Policies\
System
DisableRegistryTools = "dword:00000000"

HKEY_CURRENT_USER\Software\Policies\
Microsoft\Windows\System
DisableCMD = "dword:00000000"

It modifies the following registry entries:

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Explorer\
Advanced
Hidden = "dword:00000001"

(Note: The default value data of the said registry entry is dword:00000002.)

Propagation

This worm drops the following copy(ies) of itself in all removable drives:

  • {removable drive letter}:\Microsoft.dat

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]
ShElLEXeCuTE=WScRiPt.EXe /e:VBScRIpt.eNcOdE miCroSoFt.dat

Dropping Routine

This worm drops the following files:

  • %Windows%\svchost .exe

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

NOTES:

It drops the following shortcut pointing to its copy in all removable drive:

  • -{removable drive letter}:\{user name}.lnk

The dropped copies of itself in removable drives are set to Hidden.