WORM_BRONTOK.HP
Windows 2000, Windows XP, Windows Server 2003
Threat Type: Worm
Destructiveness: No
Encrypted:
In the wild: Yes
OVERVIEW
This worm arrives as an attachment to email messages spammed by other malware/grayware or malicious users. It arrives by connecting affected removable drives to a system. 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 Windows Task Scheduler to add a scheduled task that executes the copies it drops.
It modifies files, disabling programs and applications from properly running. It disables Task Manager, Registry Editor, and Folder Options.
TECHNICAL DETAILS
Arrival Details
This worm arrives as an attachment to email messages spammed by other malware/grayware or malicious users.
It arrives by connecting affected removable drives to a system.
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:
- %Application Data%\br{random}on.exe
- %Application Data%\csrss.exe
- %Application Data%\inetinfo.exe
- %Application Data%\lsass.exe
- %Application Data%\services.exe
- %Application Data%\smss.exe
- %Application Data%\svchost.exe
- %Application Data%\winlogon.exe
- %System%\CMD-BRO-{random}.EXE
- %System%\DXBLBV.exe
- %System%\{user name}'S SETTING.SCR
- %User Profile%\TEMPLATES\{random}-NENDANGBRO.COM
- %Windows%\SEMBAKO-{random}.EXE
- %Windows%\SHELLNEW\BBM-{random}.exe
- %System%\drivers\etc\HOSTS-DENIED BY-{USER NAME}.COM
(Note: %Application Data% is the current user's Application Data folder, which is usually C:\Windows\Profiles\{user name}\Application Data on Windows 98 and ME, C:\WINNT\Profiles\{user name}\Application Data on Windows NT, and C:\Documents and Settings\{user name}\Local Settings\Application Data on Windows 2000, XP, and Server 2003.. %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.. %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.. %Windows% is the Windows folder, which is usually C:\Windows or C:\WINNT.)
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-{random} = "%Application Data%\{br{random}on.exe"
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\CurrentVersion\Run
Bron-Spizaetus-{random} = "%Windows%\ShellNew\bbm-{random}.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%\sembako-{random}"
(Note: The default value data of the said registry entry is "Explorer.exe".)
It drops the following file(s) in the Windows User Startup folder to enable its automatic execution at every system startup:
- %User Startup%\Empty.pif – copy of itself
(Note: %User Startup% is the current user's Startup folder, which is usually C:\Windows\Profiles\{user name}\Start Menu\Programs\Startup on Windows 98 and ME, C:\WINNT\Profiles\{user name}\Start Menu\Programs\Startup on Windows NT, and C:\Documents and Settings\{User name}\Start Menu\Programs\Startup.)
Other System Modifications
This worm modifies the following files:
- %System Root%\AUTOEXEC.BAT
(Note: %System Root% is the root folder, which is usually C:\. It is also where the operating system is located.)
It modifies the following registry entries:
HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\
Control\SafeBoot
AlternateShell = "cmd-bro-{random}.exe"
(Note: The default value data of the said registry entry is cmd.exe.)
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\
System
DisableCMD = "0"
HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Policies\
Explorer
NoFolderOptions = "1"
Dropping Routine
This worm drops the following files:
- %System%\sistem.sys
(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.)
Other Details
This worm connects to the following possibly malicious URL:
- http://www.{BLOCKED}b.com/Kids/droppt
SOLUTION
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
Terminate a malware/grayware process
*Note: If the detected process is not displayed in theWindows Task Manager, continue doing the next steps.
- %Application Data%\br{random}on.exe
- %Application Data%\csrss.exe
- %Application Data%\inetinfo.exe
- %Application Data%\lsass.exe
- %Application Data%\services.exe
- %Application Data%\smss.exe
- %Application Data%\svchost.exe
- %Application Data%\winlogon.exe
- %System%\CMD-BRO-{random}.EXE
- %System%\DXBLBV.exe
- %System%\{user name}'S SETTING.SCR
- %User Profile%\TEMPLATES\{random}-NENDANGBRO.COM
- %Windows%\SEMBAKO-{random}.EXE
- %Windows%\SHELLNEW\BBM-{random}.exe
- %System%\drivers\etc\HOSTS-DENIED BY-{USER NAME}.COM
Step 3
Delete this registry value
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-{random} = "%Application Data%\{br{random}on.exe"
- Tok-Cirrhatus-{random} = "%Application Data%\{br{random}on.exe"
- In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Run
- Bron-Spizaetus-{random} = "%Windows%\ShellNew\bbm-{random}.exe"
- Bron-Spizaetus-{random} = "%Windows%\ShellNew\bbm-{random}.exe"
- In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Policies\System
- DisableRegistryTools = "1"
- DisableRegistryTools = "1"
- In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Policies\System
- DisableCMD = "0"
- DisableCMD = "0"
- In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Policies\Explorer
- NoFolderOptions = "1"
- NoFolderOptions = "1"
Step 4
Restore this modified registry value
Important: Editing the Windows Registry incorrectly can lead to irreversible system malfunction. Please do this only if you know how to or you can seek your system administrator’s help. You may also check out 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%\sembako-{random}"
To: Shell = "Explorer.exe"
- From: Shell = "Explorer.exe %Windows%\sembako-{random}"
- In HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\Control\SafeBoot
- From: AlternateShell = "cmd-bro-{random}.exe"
To: AlternateShell = "cmd.exe"
- From: AlternateShell = "cmd-bro-{random}.exe"
- In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\Advanced
- From: Hidden = "0"
To: Hidden = "1"
- From: Hidden = "0"
- In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\Advanced
- From: HideFileExt = "1"
To: HideFileExt = "0"
- From: HideFileExt = "1"
- In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\Advanced
- From: "ShowSuperHidden" = "0"
To: "ShowSuperHidden" = "1"
- From: "ShowSuperHidden" = "0"
Step 5
Search and delete this file
- %System%\sistem.sys
Step 6
Scan your computer with your Trend Micro product to delete files detected as WORM_BRONTOK.HP. 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 7
Restore deleted/modified files and/or registry entries from backup
*Note: Only Microsoft-related files/keys/values will be restored. If this malware/grayware also deleted registry keys/values related to programs that are not from Microsoft, please reinstall those programs on your computer.
- %System Root%\AUTOEXEC.bat
Did this description help? Tell us how we did.