Analysis by: Jaime Benigno Reyes
ALIASES:

Generic PWS.g (McAfee), Infostealer.Lineage (Symantec), Troj/Gampass-A (Sophos), Worm:Win32/Autorun.NN (Microsoft)

 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 may be downloaded by other malware/grayware/spyware from remote sites. It may be unknowingly downloaded by a user while visiting malicious websites.

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: 36,864 bytes
File Type: EXE
Memory Resident: Yes
Initial Samples Received Date: 09 Oct 2012

Arrival Details

This worm may be downloaded by other malware/grayware/spyware from remote sites.

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:

  • %System%\EXPLORER.EXE

(Note: %System% is the Windows system folder, which is usually C:\Windows\System32.)

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
EXPLORER.EXE = "EXPLORER.EXE"

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Run
wsctf.exe = "wsctf.exe"

It modifies the following registry entries to ensure it automatic execution at every system startup:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows NT\CurrentVersion\Winlogon
Userinit = "userinit.exe,EXPLORER.EXE"

(Note: The default value data of the said registry entry is "%System%\userinit.exe".)

Propagation

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

  • {drive letter}:\EXPLORER.EXE

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=EXPLORER.EXE
shell\open\Command=EXPLORER.EXE
shell\open\Default=1
shell\explore\Command=EXPLORER.EXE

  SOLUTION

Minimum Scan Engine: 9.200
FIRST VSAPI PATTERN FILE: 4.506.19
FIRST VSAPI PATTERN DATE: 03 Jun 2007
VSAPI OPR PATTERN File: 4.507.00
VSAPI OPR PATTERN Date: 03 Jun 2007

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

Identify and terminate files detected as WORM_VB.DVP

[ Learn More ]
  1. Windows Task Manager may not display all running processes. In this case, please use a third-party process viewer, preferably Process Explorer, to terminate the malware/grayware/spyware file. You may download the said tool here.
  2. If the detected file is displayed in either Windows Task Manager or Process Explorer but you cannot delete it, restart your computer in safe mode. To do this, refer to this link for the complete steps.
  3. If the detected file is not displayed in either Windows Task Manager or Process Explorer, continue doing the next steps.

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\Run
    • EXPLORER.EXE = "EXPLORER.EXE"
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Run
    • wsctf.exe = "wsctf.exe"

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_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon
    • From: Userinit = "userinit.exe,EXPLORER.EXE"
      To: Userinit = "%System%\userinit.exe"

Step 5

Search and delete AUTORUN.INF files created by WORM_VB.DVP that contain these strings

[ Learn More ]

[Autorun]
OPEN=EXPLORER.EXE
shell\open\Command=EXPLORER.EXE
shell\open\Default=1
shell\explore\Command=EXPLORER.EXE

Step 6

Scan your computer with your Trend Micro product to delete files detected as WORM_VB.DVP. 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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