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Worm:W32/Brontok.B

Classification

Category:Malware
Type:Worm
Platform:W32
Aliases:

Worm.Win32.Brontok.b

Summary

Net-Worm:W32/Brontok.B attempts to propagate over removable media such as USB thumb drives. It may also attempt to connect to remote servers. Brontok.B disables certain features of the operating system.

Removal

Based on the settings of your F-Secure security product, it will either move the file to the quarantine where it cannot spread or cause harm, or remove it.

Note

To fix executable file associations after disinfection please download and run the following Registry fix:

A False Positive is when a file is incorrectly detected as harmful, usually because its code or behavior resembles known harmful programs. A False Positive will usually be fixed in a subsequent database update without any action needed on your part. If you wish, you may also:

  • Check for the latest database updates

    First check if your F-Secure security program is using the latest updates, then try scanning the file again.

  • Submit a sample

    After checking, if you still believe the file is incorrectly detected, you can submit a sample of it for re-analysis.

    Note: If the file was moved to quarantine, you need to collect the file from quarantine before you can submit it.

  • Exclude a file from further scanning

    If you are certain that the file is safe and want to continue using it, you can exclude it from further scanning by the F-Secure security product.

    Note: You need administrative rights to change the settings.

Technical Details

Execution

On execution, the first noticeable characteristic from this malware is the termination of applications such as CMD, regedit, and other EXE files. Processes with the following strings are terminated by this malware:

  • ANT
  • ASM
  • AVAST
  • BUG
  • CONF
  • CONSO
  • DBG
  • DETEC
  • INSTALL
  • KASP
  • MCAFEE
  • NOD
  • NORTON
  • NTVDM
  • OPEN
  • PLAY
  • PROC
  • REG
  • REMOV
  • SCAN
  • SECUR
  • SUPPO
  • TASK
  • UPDAT
  • UPG
  • VIR
  • W32
  • WALK

Furthermore, this malware will not perform any system changes if its filename is any of the following:

  • AutoPro.exe
  • mdefault.exe
  • mcagent.exe
  • mcshield.exe

During execution, the following files are dropped:

  • C:\AUTORUN.INF
  • C:\Documents and Settings\\Local Settings\Temp\~DF1A17.tmp
  • C:\Documents and Settings\All Users\Start Menu\Programs\Startup\Empty.pif
  • C:\WINDOWS\Autorun.inf
  • C:\WINDOWS\Web\shell.exe
  • C:\WINDOWS\winme.exe
  • C:\winme.exe

Activity

This worm may open a browser attempting to connect to the following URLs:

  • https://security.symantec.com
  • https://www.symantec.com

Propagation

Brontok.B will create AUTORUN.INF files and copy itself to available removable media (USB drives) to allow itself to propagate.

Registry Modifications

Sets these values:

  • [HKCR\batfile\shell\open\command] (default) = "C:\WINDOWS\web\shell.exe" "%1" %*
  • [HKCR\comfile\shell\open\command] (default) = "C:\WINDOWS\web\shell.exe" "%1" %*
  • [HKCR\exefile\shell\open\command] (default) = "C:\WINDOWS\web\shell.exe" "%1" %*
  • [HKCR\piffile\shell\open\command] (default) = "C:\WINDOWS\web\shell.exe" "%1" %*
  • [HKCU\Software\Microsoft\Windows\CurrentVersion\Explorer\Advanced] Hidden = 1 HideFileExt = 1 ShowSuperHidden = 1
  • [HKCU\Software\Microsoft\Windows\CurrentVersion\Policies\System] DisableTaskMgr = 1 DisableRegistryTools = 1 DisableCMD = 1
  • [HKCU\Software\Microsoft\Windows\CurrentVersion\Policies\Explorer] Nofolderoptions = 1
  • [HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\policies\system] DisableTaskMgr = 1 DisableRegistryTools = 1
  • [HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\policies\Explorer] NoFolderOptions = 1
  • [HKLM\SOFTWARE\Policies\Microsoft\Windows\Installer] DisableMSI = 1
  • [HKLM\SOFTWARE\Policies\Microsoft\Windows NT\SystemRestore] DisableConfig = 1 DisableSR = 1
  • [HKLM\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon\ Shell = Explorer.exe "C:\WINDOWS\winme.exe" Userinit = C:\WINDOWS\System32\userinit.exe,C:\WINDOWS\winme.exe
  • [HKLM\SYSTEM\ControlSet001\Control\SafeBoot\ AlternateShell = C:\WINDOWS\winme.exe
  • [HKLM\SYSTEM\CurrentControlSet\Control\SafeBoot\ AlternateShell = C:\WINDOWS\winme.exe

Deletes these keys:

  • [HKCU\Software\Microsoft\Windows\CurrentVersion\Run\] winme = C:\WINDOWS\winme.exe
  • [HKCR\lnkfile\shell\open\command\] (default) = "C:\WINDOWS\web\shell.exe" "%1" %*

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