WORM_RONTKBR.GEN

 Analysis by: Carl Maverick Pascual

 ALIASES:

W32.Rontokbro@mm (Symantec), Worm:Win32/Brontok@mm (Microsoft), Email-Worm.Win32.Brontok.q (Kaspersky)

 PLATFORM:

Windows

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

  • Threat Type: Worm

  • Destructiveness: No

  • Encrypted:

  • In the wild: Yes

  OVERVIEW

Infection Channel:

Spammed via email, Dropped by other malware, Downloaded from the Internet

This Worm arrives as attachment to mass-mailed email messages. 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 uses the default Windows folder icon to trick users into opening the file. Double-clicking the file executes this malware.

However, as of this writing, the said sites are inaccessible.

  TECHNICAL DETAILS

File Size:

51,910 bytes

File Type:

EXE

Memory Resident:

No

Payload:

Connects to URLs/IPs, Restarts system

Arrival Details

This Worm arrives as attachment to mass-mailed email messages.

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%\ShellNew\sempalong.exe
  • %Windows%\BerasJatah.exe
  • %AppDataLocal%\csrss.exe
  • %System Root%\autoexec.bat
  • %User Startup%\Empty.pif
  • %ApplicationData%\Microsoft\Windows\Templates\Brengkolang.com

It drops the following copies of itself into the affected system and executes them:

  • %AppDataLocal%\smss.exe
  • %AppDataLocal%\services.exe
  • %AppDataLocal%\lsass.exe
  • %AppDataLocal%\inetinfo.exe
  • %AppDataLocal%\winlogon.exe

(Note: %AppDataLocal% is the Local Application Data folder, which is usually C:\Documents and Settings\{user name}\Local Settings\Application Data on Windows 2000, XP, and Server 2003, or C:\Users\{user name}\AppData\Local on Windows Vista, 7, and 8.)

It creates the following folders:

  • %AppDataLocal%\Bron.tok-{mm}-{dd}

(Note: %AppDataLocal% is the Local Application Data folder, which is usually C:\Documents and Settings\{user name}\Local Settings\Application Data on Windows 2000, XP, and Server 2003, or C:\Users\{user name}\AppData\Local on Windows Vista, 7, and 8.)

It uses the default Windows folder icon to trick users into opening the file. Double-clicking the file executes this malware.

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
Tok-Cirrhatus = "%AppDataLocal%\smss.exe"

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\CurrentVersion\Run
Bron-Spizaetus = "%Windows%\ShellNew\sempalong.exe"

It modifies the following entry(ies) to allow itself to run on safe mode:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows NT\CurrentVersion\Winlogon
Shell = Explorer.exe "%Windows%\BerasJatah.exe"

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

Other System Modifications

This Worm modifies the following registry entries:

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Policies\
System
DisableCMD = 0

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

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Policies\
Explorer
NoFolderOptions = 1

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

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Explorer\
Advanced
Hidden = 0

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

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

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

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\Policies\
System
DisableRegistryTools = 1

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

Dropping Routine

This Worm drops the following files:

  • %AppDataLocal%\Update.14.Bron.Tok.bin

(Note: %AppDataLocal% is the Local Application Data folder, which is usually C:\Documents and Settings\{user name}\Local Settings\Application Data on Windows 2000, XP, and Server 2003, or C:\Users\{user name}\AppData\Local on Windows Vista, 7, and 8.)

Other Details

This Worm connects to the following possibly malicious URL:

  • http://www.{BLOCKED}ies.com/sbllma5/IN14WHOXOLPD.txt
  • http://www.{BLOCKED}ies.com/sblppt4/IN14SDSDWWHOX.txt

It sets the attributes of the following file(s) to Hidden and System:

  • %System Root%\autoexec.bat
  • %Windows%\ShellNew\sempalong.exe
  • %Windows%\BerasJatah.exe

(Note: %System Root% is the Windows root folder, where it usually is C:\ on all Windows operating system versions.. %Windows% is the Windows folder, where it usually is C:\Windows on all Windows operating system versions.)

It does the following:

  • Payload 1: Restarts system
  • Trigger condition: Upon detection of certain strings in browser window title bar
  • Payload 2: Disables Registry Editor and Task Manager

However, as of this writing, the said sites are inaccessible.

  SOLUTION

Minimum Scan Engine:

9.850

FIRST VSAPI PATTERN FILE:

6.106.04

FIRST VSAPI PATTERN DATE:

04 May 2009

VSAPI OPR PATTERN File:

6.107.00

VSAPI OPR PATTERN Date:

04 May 2009

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

Note that not all files, folders, and registry keys and entries are installed on your computer during this malware's/spyware's/grayware's execution. This may be due to incomplete installation or other operating system conditions. If you do not find the same files/folders/registry information, please proceed to the next step.

Step 3

Restart in Safe Mode

[ Learn More ]

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_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Run
    • Bron-Spizaetus = "%Windows%\ShellNew\sempalong.exe"
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Policies\System
    • DisableCMD = "0"
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Run
    • Tok-Cirrhatus = "%AppDataLocal%\smss.exe"

Step 5

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\System
    • From: DisableRegistryTools = "1"
      To: DisableRegistryTools = "0"
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon
    • From: Shell = "Explorer.exe "%Windows%\BerasJatah.exe""
      To: Shell = "Explorer.exe"
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Policies\Explorer
    • From: NoFolderOptions = "1"
      To: NoFolderOptions = "0"
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\Advanced
    • From: Hidden = "1"
      To: Hidden = "0"
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\Advanced
    • From: HideFileExt = "1"
      To: HideFileExt = "0"
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\Advanced
    • From: ShowSuperHidden = "0"
      To: ShowSuperHidden = "1"

Step 6

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.
  • %AppDataLocal%\\Bron.tok-{mm}-{dd}

Step 7

Search and delete these files

[ Learn More ]
There may be some 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.
  • %Windows%\ShellNew\sempalong.exe
  • %Windows%\BerasJatah.exe
  • %AppDataLocal%\smss.exe
  • %AppDataLocal%\services.exe
  • %AppDataLocal%\lsass.exe
  • %AppDataLocal%\inetinfo.exe
  • %AppDataLocal%\csrss.exe
  • %AppDataLocal%\winlogon.exe
  • %System Root%\autoexec.bat
  • %User Startup%\Empty.pif
  • %Application Data%\Microsoft\Windows\Templates\Brengkolang.com
  • %System%\{username}'s Setting.scr

Step 8

Restart in normal mode and scan your computer with your Trend Micro product for files detected as WORM_RONTKBR.GEN. 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.

Step 9

Scan your computer with your Trend Micro product to delete files detected as WORM_RONTKBR.GEN. 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 the following Trend Micro Support pages for more information:


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