Analysis by: JessaD
ALIASES:

Trojan-Downloader.Win32.VB.aefx (Kaspersky), Downloader (Symantec)

 PLATFORM:

Windows 2000, XP, Server 2003

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

  • Threat Type: Trojan

  • Destructiveness: No

  • Encrypted: Yes

  • In the wild: Yes

  OVERVIEW

This Trojan may be downloaded by other malware/grayware/spyware from remote sites. It may be dropped by other malware.

It modifies the user's Internet Explorer home page into a certain website. This action allows the malware to point to a website which may contain malware, putting the affected computer at greater risk of malware infection.

  TECHNICAL DETAILS

File Size: 47,104 bytes
File Type: PE
Memory Resident: Yes
Initial Samples Received Date: 16 Feb 2011

Arrival Details

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

It may be dropped by other malware.

Installation

This Trojan drops the following component file(s):

  • %User Profile%\Application Data\{random characters}.txt - detected as TROJ_SMALL.WTU

(Note: %User Profile% is the current user's profile folder, which is usually C:\Windows\Profiles\{user name} on Windows 98 and ME, C:\WINNT\Profiles\{user name} on Windows NT, and C:\Documents and Settings\{user name} on Windows 2000, XP, and Server 2003.)

It drops the following copies of itself into the affected system:

  • %User Profile%\Application Data\windows32.exe

(Note: %User Profile% is the current user's profile folder, which is usually C:\Windows\Profiles\{user name} on Windows 98 and ME, C:\WINNT\Profiles\{user name} on Windows NT, and C:\Documents and Settings\{user name} on Windows 2000, XP, and Server 2003.)

Its DLL component is injected to the following process(es):

  • explorer.exe

It adds the following mutexes to ensure that only one of its copies runs at any one time:

  • WeAreWeAre

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\Policies\
Explorer\Run
MicrosoftWindows = %User Profile%\Application Data\windows32.exe

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Run
MicrosoftWindows = %User Profile%\Application Data\windows32.exe

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\RunOnce
MicrosoftWindows = %User Profile%\Application Data\windows32.exe

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\RunServices
MicrosoftWindows = %User Profile%\Application Data\windows32.exe

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\RunServicesOnce
MicrosoftWindows = %User Profile%\Application Data\windows32.exe

HKEY_CURRENT_USER\Software\Microsoft\
Windows NT\CurrentVersion\Windows\
load
MicrosoftWindows = %User Profile%\Application Data\windows32.exe

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\CurrentVersion\policies\
Explorer\Run
MicrosoftWindows = %User Profile%\Application Data\windows32.exe

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\CurrentVersion\Run
MicrosoftWindows = %User Profile%\Application Data\windows32.exe

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\CurrentVersion\RunOnce
MicrosoftWindows = %User Profile%\Application Data\windows32.exe

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\CurrentVersion\RunServices
MicrosoftWindows = %User Profile%\Application Data\windows32.exe

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\CurrentVersion\RunServicesOnce
MicrosoftWindows = %User Profile%\Application Data\windows32.exe

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows NT\CurrentVersion\Windows\
load
MicrosoftWindows = %User Profile%\Application Data\windows32.exe

Other System Modifications

This Trojan modifies the following registry entries:

HKEY_CURRENT_USER\Software\Microsoft\
Internet Explorer\Main
Start Page = http://redirecturls.info/

(Note: The default value data of the said registry entry is about:blank.)

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\CurrentVersion
Start Page = http://redirecturls.info/

(Note: The default value data of the said registry entry is about:blank.)

Web Browser Home Page and Search Page Modification

This Trojan modifies the user's Internet Explorer home page to the following websites:

  • http://{BLOCKED}cturls.info/

  SOLUTION

Minimum Scan Engine: 8.900
VSAPI PATTERN File: 7.840.06
VSAPI PATTERN Date: 16 Feb 2011
VSAPI PATTERN Date: 2/16/2011 12:00:00 AM

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

Remove malware files dropped/downloaded by TROJ_VBNA.WZM

     TROJ_SMALL.WTU

Step 3

Identify and terminate files detected as TROJ_VBNA.WZM

[ Learn More ]
  1. 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.
  2. If the detected file is not displayed in either Windows Task Manager or Process Explorer, continue doing the next steps.

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_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Policies\Explorer\Run
    • MicrosoftWindows = %User Profile%\Application Data\windows32.exe
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Run
    • MicrosoftWindows = %User Profile%\Application Data\windows32.exe
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\RunOnce
    • MicrosoftWindows = %User Profile%\Application Data\windows32.exe
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\RunServices
    • MicrosoftWindows = %User Profile%\Application Data\windows32.exe
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\RunServicesOnce
    • MicrosoftWindows = %User Profile%\Application Data\windows32.exe
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows NT\CurrentVersion\Windows\load
    • MicrosoftWindows = %User Profile%\Application Data\windows32.exe
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\policies\Explorer\Run
    • MicrosoftWindows = %User Profile%\Application Data\windows32.exe
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Run
    • MicrosoftWindows = %User Profile%\Application Data\windows32.exe
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\RunOnce
    • MicrosoftWindows = %User Profile%\Application Data\windows32.exe
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\RunServices
    • MicrosoftWindows = %User Profile%\Application Data\windows32.exe
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\RunServicesOnce
    • MicrosoftWindows = %User Profile%\Application Data\windows32.exe
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Windows\load
    • MicrosoftWindows = %User Profile%\Application Data\windows32.exe

Step 5

Reset the Internet Explorer Home and Search pages

[ Learn More ]

Step 6

Scan your computer with your Trend Micro product to delete files detected as TROJ_VBNA.WZM. 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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