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VBS_SASAN.A

October 09, 2012
 Analysis by: Rhena Inocencio
 PLATFORM:

Windows 2000, Windows XP, Windows Server 2003

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

  • Threat Type: Worm

  • Destructiveness: No

  • Encrypted:

  • In the wild: Yes

  OVERVIEW


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 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:

1,082,726 bytes

File Type:

VBS

Memory Resident:

No

Initial Samples Received Date:

29 Sep 2011

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:

  • %Windows%\.MS32DLL.dll.vbs
  • %Windows%\boot.ini
  • %User Temp%\boot.{number}

(Note: %Windows% is the Windows folder, which is usually C:\Windows or C:\WINNT.. %User Temp% is the current user's Temp folder, which is usually C:\Documents and Settings\{user name}\Local Settings\Temp on Windows 2000, XP, and Server 2003.)

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
MS32DLL = "%Windows%\.MS32DLL.dll.vbs"

HKEY_LOCAL_MACHINE\Software\Microsoft\
Windows\CurrentVersion\Run\
winboot
wscript.exe = "%Windows%\boot.ini"

Other System Modifications

This worm adds the following registry entries:

HKEY_CURRENT_USER\Software\Microsoft\
Windows Scripting Host\Settings
Timeout = "0"

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Explorer\
Advanced
HideFileExt = "1"

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Explorer\
Advanced
Hidden = "1"

It modifies the following registry entries to hide files with Hidden attributes:

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Explorer\
Advanced
ShowSuperHidden = "0"

(Note: The default value data of the said registry entry is "1".)

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Explorer\
Advanced
SuperHidden = "1"

(Note: The default value data of the said registry entry is "0".)

Propagation

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

  • .MS32DLL.dll.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]
shellexecute=wscript.exe .MS32DLL.dll.vbs

  SOLUTION

Minimum Scan Engine:

9.200

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

Search and delete AUTORUN.INF files created by VBS_SASAN.A that contain these strings

[ Learn More ]
[autorun]
shellexecute=wscript.exe .MS32DLL.dll.vbs

Step 3

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\Explorer\Advanced
    • HideFileExt = "1"
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\Advanced
    • Hidden = "1"
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows Scripting Host\Settings
    • Timeout = "0"
  • In HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Run
    • MS32DLL = "%Windows%\.MS32DLL.dll.vbs"
  • In HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Run\winboot
    • wscript.exe = "%Windows%\boot.ini"

Step 4

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\Policies\Explorer
    • From: NoDriveTypeAutoRun = "0"
      To: NoDriveTypeAutoRun = "91"
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\Advanced
    • From: SuperHidden = "1"
      To: SuperHidden = "0"
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\Advanced
    • From: ShowSuperHidden = "0"
      To: ShowSuperHidden = "1"

Step 5

Scan your computer with your Trend Micro product to delete files detected as VBS_SASAN.A. 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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