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WORM_BRONTOK.FL

October 08, 2012
 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

Infection Channel:

Propagates via removable drives

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 copies of itself into all the removable drives connected to an affected system.

  TECHNICAL DETAILS

File Size:

1,006,592 bytes

File Type:

EXE

Memory Resident:

No

Initial Samples Received Date:

09 Feb 2011

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:

  • %System Root%\AUT0EXEC.BAT
  • %Windows%\system32.exe
  • %System%\dllchache\Blank.doc
  • %System%\dllchache\Empty.jpg
  • %System%\dllchache\Hole.zip
  • %System%\dllchache\Unoccupied.reg
  • %System%\dllchache\Zero.txt
  • %System%\M5VBVM60.EXE
  • %System%\dllcache\Regedit32.com
  • %System%\dllcache\Shell32.com
  • %System%\dllchache\Empty.jpg

It drops the following files:

  • %System Root%\(Read Me)Pendekar Blank.txt
  • %System Root%\msvbvm60.dll
  • %System%\dllchache\msvbvm60.dll
  • %System%\dllchache.exe
  • %System%\rund1132.exe
  • %System%\dllcache\msvbvm60.dll
  • %System%\drivers\iopfqo.sys
  • %Current Folder%\{malware name}
  • %System%\mm304929.dll
  • %System%\mm304929.dl_
  • %System%\mm304929.dll

(Note: %System Root% is the root folder, which is usually C:\. It is also where the operating system is located.. %System% is the Windows system folder, which is usually C:\Windows\System on Windows 98 and ME, C:\WINNT\System32 on Windows NT and 2000, or C:\Windows\System32 on Windows XP and Server 2003.)

It creates the following folders:

  • %System%\dllchache

(Note: %System% is the Windows system folder, which is usually C:\Windows\System on Windows 98 and ME, C:\WINNT\System32 on Windows NT and 2000, or C:\Windows\System32 on Windows XP and Server 2003.)

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
Secure64 = %System%\dllcache\Regedit32.com StartUp

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Run
Secure32 = %System%\dllcache\Shell32.com StartUp

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\CurrentVersion\Run
Blank AntiViri = %System Root%\AUT0EXEC.BAT StartUp

Other System Modifications

This worm adds the following registry entries as part of its installation routine:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\CurrentVersion\policies\
system
EnableLUA = 0

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\SharedAccess\Parameters\
FirewallPolicy\StandardProfile\AuthorizedApplications\
List
\??\%system%\winlogon.exe = \??\%system%\winlogon.exe:*:enabled:@shell32.dll,-1

It modifies the following registry entries:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Control\SafeBoot
AlternateShell = %System Root%\AUT0EXEC.BAT StartUp

(Note: The default value data of the said registry entry is cmd.exe.)

Propagation

This worm drops copies of itself into all the removable drives connected to an affected system.

  SOLUTION

Minimum Scan Engine:

8.900

FIRST VSAPI PATTERN FILE:

7.824.01

FIRST VSAPI PATTERN DATE:

09 Feb 2011

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_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Run
    • Secure64 = %System%\dllcache\Regedit32.com StartUp
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Run
    • Secure32 = %System%\dllcache\Shell32.com StartUp
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Run
    • Blank AntiViri = %System Root%\AUT0EXEC.BAT StartUp
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\policies\system
    • EnableLUA = 0
  • In HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\SharedAccess\Parameters\FirewallPolicy\StandardProfile\AuthorizedApplications\List
    • \??\%System%\winlogon.exe = \??\%System%\winlogon.exe:*:enabled:@shell32.dll,-1

Step 3

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\SYSTEM\CurrentControlSet\Control\SafeBoot
    • From: AlternateShell = %System Root%\AUT0EXEC.BAT StartUp
    • To: AlternateShell = cmd.exe

Step 4

Search and delete these folders

[ Learn More ]
Please make sure you check the Search Hidden Files and Folders checkbox in the More advanced options option to include all hidden folders in the search result. %System%\dllchache

Step 5

Search and delete this file

[ Learn More ]
There may be some component files that are hidden. Please make sure you check the Search Hidden Files and Folders checkbox in the More advanced options option to include all hidden files and folders in the search result.
%System Root%\(Read Me)Pendekar Blank.txt
%System Root%\msvbvm60.dll
%System%\dllchache.exe
%System%\rund1132.exe
%System%\drivers\iopfqo.sys
%Current Folder%\{malware name}
%System%\mm304929.dll
%System%\mm304929.dl_

Step 6

Scan your computer with your Trend Micro product to delete files detected as WORM_BRONTOK.FL. 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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