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WORM_BRONTOK.DNM

August 21, 2018
 Analysis by: John Donnie Celestre
 ALIASES:

Worm:Win32/Brontok (MICROSOFT); Win32/Brontok.EA worm (NOD32)

 PLATFORM:

Windows 2000, XP, Server 2003

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

  • Threat Type: Worm

  • Destructiveness: No

  • Encrypted:

  • In the wild: Yes

  OVERVIEW


This Worm uses the Windows Task Scheduler to add a scheduled task that executes the copies it drops.

It disables Task Manager, Registry Editor, and Folder Options.

  TECHNICAL DETAILS

File Size:

103,047 bytes

File Type:

EXE

Memory Resident:

Yes

Initial Samples Received Date:

06 Aug 2018

Installation

This Worm drops the following files:

  • %System Root%\autoexec.bat
  • %AppDataLocal%\BronNetDomList.bat
  • %User Profile%\Pictures\about.Brontok.A.html

(Note: %System Root% is the Windows root folder, where it usually is C:\ on all Windows operating system versions.. %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.. %User Profile% is the current user's profile folder, which is usually C:\Documents and Settings\{user name} on Windows 2000, XP, and Server 2003, or C:\Users\{user name} on Windows Vista, 7, and 8.)

It drops and executes the following files:

  • %AppDataLocal%\inetinfo.exe
  • %AppDataLocal%\winlogon.exe
  • %AppDataLocal%\smss.exe
  • %AppDataLocal%\services.exe
  • %AppDataLocal%\lsass.exe
  • %AppDataLocal%\csrss.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 drops the following copies of itself into the affected system:

  • %Windows%\ShellNew\bronstab.exe
  • %Windows%\eksplorasi.pif
  • %AppDataLocal%\smss.exe
  • %AppDataLocal%\services.exe
  • %AppDataLocal%\lsass.exe
  • %AppDataLocal%\inetinfo.exe
  • %AppDataLocal%\csrss.exe
  • %AppDataLocal%\winlogon.exe
  • %User Startup%\Empty.pif
  • %System%\{username}'s Setting.scr
  • %System%\drivers\etc\hosts-Denied By-{username}.com
  • %Application Data%\Microsoft\Windows\Templates\WowTumpeh.com

It uses the Windows Task Scheduler to add a scheduled task that executes the copies it drops.

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 = %Application Data%\smss.exe

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\CurrentVersion\Run
Bron-Spizaetus = %Windows%\ShellNew\bronstab.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
Shell = explorer.exe %Windows%\eksplorasi.pif

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

The scheduled task executes the malware every:

  • 5:08 PM every day

Other System Modifications

This Worm adds the following registry entries:

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

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\Schedule
AtTaskMaxHours = 48

It modifies the following registry entries:

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.)

It creates the following registry entry(ies) to disable Task Manager, Registry Tools and Folder Options:

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Policies\
System
DisableRegistryTools = 1

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

Propagation

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

  • {drive letter}:\Data {username}.exe

Process Termination

This Worm terminates the following processes if found running in the affected system's memory:

  • mcvsescn.exe
  • poproxy.exe
  • avgemc.exe
  • ccapps.exe

Dropping Routine

This Worm drops the following files:

  • %AppDataLocal%\Bron.tok.A8.em.bin
  • %AppDataLocal%\Update.8.Bron.Tok.bin
  • %AppDataLocal%\Kosong.Bron.Tok.txt
  • %AppDataLocal%\BronNPath0.txt
  • %AppDataLocal%\ListHost8.txt
  • %AppDataLocal%\BronFoldNetDomList.txt
  • %AppDataLocal%\Loc.Mail.Bron.Tok\{email}.ini

(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 URL(s) to check for an Internet connection:

  • israel.gov.il
  • playboy.com

It connects to the following possibly malicious URL:

  • http://www.{BLOCKED}ties.com/stabro7ok/BrontokInf8.txt
  • http://www.{BLOCKED}ties.com/stabro7ok/Host8.txt
  • http://www.{BLOCKED}ies.com/stabro7ok/Bron-ID8.txt

  SOLUTION

Minimum Scan Engine:

9.5

FIRST VSAPI PATTERN FILE:

14.446.04

FIRST VSAPI PATTERN DATE:

16 Aug 2018

VSAPI OPR PATTERN File:

14.447.00

VSAPI OPR PATTERN Date:

17 Aug 2018

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

Enable Registry Editor, Task Manager, and Folder options

[ Learn More ]
By doing this step, you also enable other applications/programs disabled by this malware/grayware/spyware.

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_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon
    • From: Shell = explorer.exe %Windows%\eksplorasi.pif
      To: Shell = explorer.exe
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\Advanced
    • From: Hidden = 0
      To: Hidden = 1
  • 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

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
    • Tok-Cirrhatus = %Application Data%\smss.exe
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Run
    • Bron-Spizaetus = %Windows%\ShellNew\bronstab.exe
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Policies\System
    • DisableCMD = 0

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\bronstab.exe
  • %Windows%\eksplorasi.pif
  • %AppDataLocal%\smss.exe
  • %AppDataLocal%\services.exe
  • %AppDataLocal%\lsass.exe
  • %AppDataLocal%\inetinfo.exe
  • %AppDataLocal%\csrss.exe
  • %AppDataLocal%\winlogon.exe
  • %User Startup%\Empty.pif
  • %System%\{username}'s Setting.scr
  • %System%\drivers\etc\hosts-Denied By-{username}.com
  • %Application Data%\Microsoft\Windows\Templates\WowTumpeh.com
  • %System Root%\autoexec.bat
  • %AppDataLocal%\BronNetDomList.bat
  • %User Profile%\Pictures\about.Brontok.A.html
  • %AppDataLocal%\Bron.tok.A8.em.bin
  • %AppDataLocal%\Update.8.Bron.Tok.bin
  • %AppDataLocal%\Kosong.Bron.Tok.txt
  • %AppDataLocal%\BronNPath0.txt
  • %AppDataLocal%\ListHost8.txt
  • %AppDataLocal%\BronFoldNetDomList.txt
  • %AppDataLocal%\Loc.Mail.Bron.Tok\{email}.ini
  • {drive letter}:\Data {username}.exe

Step 8

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