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Discovered: November 03, 2008
Updated: November 03, 2008 10:58:28 PM
Also Known As: WORM_KERBOT.A [Trend], Win32/Kerbot.A [Computer Associates]
Type: Trojan, Worm
Infection Length: Varies
Systems Affected: Windows
CVE References: CVE-2008-4250

W32.Kernelbot.A is a worm that spreads by exploiting the Microsoft Windows Server Service RPC Handling Remote Code Execution Vulnerability (BID 31874) and through file sharing networks. It may also download files on to the compromised computer.

Antivirus Protection Dates

  • Initial Rapid Release version November 03, 2008 revision 021
  • Latest Rapid Release version November 04, 2019 revision 019
  • Initial Daily Certified version November 03, 2008 revision 025
  • Latest Daily Certified version November 04, 2019 revision 065
  • Initial Weekly Certified release date November 05, 2008

Click here for a more detailed description of Rapid Release and Daily Certified virus definitions.

Technical Description

The worm may arrive on to the compromised computer through network vulnerabilities or through file sharing networks.

If the worm is spread through network vulnerabilities, it may arrive as the following files:

  • 6767.exe
  • KernekDbg.exe

If the worm is spread through Peer to Peer file sharing, it may arrive as the following files:
  • keygens.exe
  • iedvv.exe

Once executed, the worm attempts to lower security settings by modifying the following registry entries:
  • HKEY_LOCAL_MACHINE\SOFTWARE\360Safe\safemon\"UDiskAccess" = "0"
  • HKEY_LOCAL_MACHINE\SOFTWARE\360Safe\safemon\"ExecAccess" = "0"
  • HKEY_LOCAL_MACHINE\SOFTWARE\360Safe\safemon\"IEProtAccess" = "0"
  • HKEY_LOCAL_MACHINE\SOFTWARE\360Safe\safemon\"LeakAccess" = "0"
  • HKEY_LOCAL_MACHINE\SOFTWARE\360Safe\safemon\"MonAccess" = "0"
  • HKEY_LOCAL_MACHINE\SOFTWARE\360Safe\safemon\"SiteAccess" = "0"

It creates some of the following files and sets the file attributes as hidden. It also changes the timestamp of these files to the legitimate Windows WINLOGON.EXE timestamp:
  • %System%\[FILE NAME].sys
  • %System%\[FILE NAME].zip
  • %System%\[FILE NAME].exe
  • %System%\[FILE NAME].dll
  • %System%\[FILE NAME].ocx
  • %System%\[FILE NAME].ini

    [FILE NAME] is a file name chosen by the remote attacker and reportedly includes the following observed file names:
  • compbatc.sys
  • compbatc.zip
  • compbatc.exe
  • vvebc1nt.sys
  • vvebc1nt.zip
  • vvebc1nt.exe

Next, it creates the following registry subkeys to register some files as Windows services and to run code in Kernel mode:
  • HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\compbatc
  • HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\compbatcDrv
  • HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\[8 NUMBERS]

It attempts to end the following processes, if found, using the newly registered services:
  • safeboxtray.exe
  • 360tray.exe
  • iparmor.exe
  • RSTray.exe
  • USBSAFE.exe
  • 360rpt.exe

It attempts to delete the following registry entries to prevent automatic execution of certain programs when Windows starts:
  • HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Run\"360Safetray"
  • HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Run\"360Safebox"
  • HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Run\"360Antiarp"
  • HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Run\"runeip"
  • HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Run\"Iparmor"

It deletes the following registry subkeys to prevent the compromised computer from restarting in Safe Mode:
  • HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\SafeBoot\Network
  • HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\SafeBoot\Minimal

Note: Deletion of the subkeys reportedly may display a Blue Screen error.

It may contact the following remote location to download commands from the attacker:

The worm is then able to perform the following actions:
  • Update itself
  • Download and execute additional malicious files
  • Download files or archives to be spread over P2P networks
  • Participate in distributed denial of service attacks against remote sites using a UDP, TCP, SYN, or HTTP flood

It reports its status and information about the compromised computer to the following Web site:

At the time of writing, the worm reportedly downloads the following files:
  • [http://]zz.ushealthmart.com/67.[REMOVED] (Bloodhound.Exploit.212)
  • [http://]st.ushealthmart.com/webc[REMOVED] (W32.Kernelbot.A)

The file 67.exe is a copy of the exploit code for the following remote vulnerability and is used to spread the worm over the local network:
Microsoft Windows Server Service RPC Handling Remote Code Execution Vulnerability (BID 31874)

The worm will download and run the following file on successfully attacked and exploited computers :
[http://]zz.ushealthmart.com/download/6767[REMOVED] (W32.Kernelbot.A)

The worm may use the webcc.exe file, if downloaded, to contact the following remote locations:
  • [http://][REMOVED]
  • [http://][REMOVED]

The worm may download or create the following files which contain custom Windows scripts to be executed on the compromised computer:

It has been observed that the worm can download and install the eMule P2P client program on the compromised computer. The eMule software is downloaded as a unique package from the following remote locations:
  • [http://]freegoogla.vicp.net/download/Loade[REMOVED] (W32.Kernelbot.A)
  • [http://]freegoogla.vicp.net/download/Demo[REMOVED] (W32.Kernelbot.A, RAR archive)
  • [http://]freegoogla.vicp.net/download/em_set[REMOVED] (W32.Kernelbot.A, sefl-extracting RAR)

When the eMule client is successfully downloaded and installed on the compromised computer, the worm tries to spread across P2P network by sharing a misleading movie file which is a copy of the worm.

It adds the following lines of text to the hosts file to prevent access to various domains:
  • 360.cn
  • alert.rising.com.cn
  • baike.360.cn
  • bbs.360.cn
  • bbs.360safe.com
  • bbs.cpcw.com
  • bbs.dswlab.com
  • bbs.duba.net
  • bbs.ikaka.com
  • bbs.janmeng.com
  • bbs.kafan.cn
  • bbs.kaspersky.com.cn
  • bbs.mcafeefans.com
  • bbs.sucop.com
  • bbs.trendmicro.com.cn
  • buy.rising.com.cn
  • center.rising.com.cn
  • cn.mcafee.com
  • cn.trendmicro.com
  • csc.rising.com.cn
  • dnl-cd1.kaspersky-labs.com
  • dnl-cd10.kaspersky-labs.com
  • dnl-cd11.kaspersky-labs.com
  • dnl-cd12.kaspersky-labs.com
  • dnl-cd13.kaspersky-labs.com
  • dnl-cd14.kaspersky-labs.com
  • dnl-cd2.kaspersky-labs.com
  • dnl-cd3.kaspersky-labs.com
  • dnl-cd4.kaspersky-labs.com
  • dnl-cd5.kaspersky-labs.com
  • dnl-cd6.kaspersky-labs.com
  • dnl-cd7.kaspersky-labs.com
  • dnl-cd8.kaspersky-labs.com
  • dnl-cd9.kaspersky-labs.com
  • dnl-cn1.kaspersky-labs.com
  • dnl-cn10.kaspersky-labs.com
  • dnl-cn11.kaspersky-labs.com
  • dnl-cn12.kaspersky-labs.com
  • dnl-cn13.kaspersky-labs.com
  • dnl-cn14.kaspersky-labs.com
  • dnl-cn15.kaspersky-labs.com
  • dnl-cn2.kaspersky-labs.com
  • dnl-cn3.kaspersky-labs.com
  • dnl-cn4.kaspersky-labs.com
  • dnl-cn5.kaspersky-labs.com
  • dnl-cn6.kaspersky-labs.com
  • dnl-cn7.kaspersky-labs.com
  • dnl-cn8.kaspersky-labs.com
  • dnl-cn9.kaspersky-labs.com
  • dnl-eu1.kaspersky-labs.com
  • dnl-eu10.kaspersky-labs.com
  • dnl-eu11.kaspersky-labs.com
  • dnl-eu12.kaspersky-labs.com
  • dnl-eu13.kaspersky-labs.com
  • dnl-eu14.kaspersky-labs.com
  • dnl-eu15.kaspersky-labs.com
  • dnl-eu2.kaspersky-labs.com
  • dnl-eu3.kaspersky-labs.com
  • dnl-eu4.kaspersky-labs.com
  • dnl-eu5.kaspersky-labs.com
  • dnl-eu6.kaspersky-labs.com
  • dnl-eu7.kaspersky-labs.com
  • dnl-eu8.kaspersky-labs.com
  • dnl-eu9.kaspersky-labs.com
  • dnl-jp1.kaspersky-labs.com
  • dnl-jp10.kaspersky-labs.com
  • dnl-jp11.kaspersky-labs.com
  • dnl-jp12.kaspersky-labs.com
  • dnl-jp13.kaspersky-labs.com
  • dnl-jp14.kaspersky-labs.com
  • dnl-jp15.kaspersky-labs.com
  • dnl-jp2.kaspersky-labs.com
  • dnl-jp3.kaspersky-labs.com
  • dnl-jp4.kaspersky-labs.com
  • dnl-jp5.kaspersky-labs.com
  • dnl-jp6.kaspersky-labs.com
  • dnl-jp7.kaspersky-labs.com
  • dnl-jp8.kaspersky-labs.com
  • dnl-jp9.kaspersky-labs.com
  • dnl-kr1.kaspersky-labs.com
  • dnl-kr10.kaspersky-labs.com
  • dnl-kr11.kaspersky-labs.com
  • dnl-kr12.kaspersky-labs.com
  • dnl-kr13.kaspersky-labs.com
  • dnl-kr14.kaspersky-labs.com
  • dnl-kr15.kaspersky-labs.com
  • dnl-kr2.kaspersky-labs.com
  • dnl-kr3.kaspersky-labs.com
  • dnl-kr4.kaspersky-labs.com
  • dnl-kr5.kaspersky-labs.com
  • dnl-kr6.kaspersky-labs.com
  • dnl-kr7.kaspersky-labs.com
  • dnl-kr8.kaspersky-labs.com
  • dnl-kr9.kaspersky-labs.com
  • dnl-ru1.kaspersky-labs.com
  • dnl-ru10.kaspersky-labs.com
  • dnl-ru11.kaspersky-labs.com
  • dnl-ru12.kaspersky-labs.com
  • dnl-ru13.kaspersky-labs.com
  • dnl-ru14.kaspersky-labs.com
  • dnl-ru15.kaspersky-labs.com
  • dnl-ru2.kaspersky-labs.com
  • dnl-ru3.kaspersky-labs.com
  • dnl-ru4.kaspersky-labs.com
  • dnl-ru5.kaspersky-labs.com
  • dnl-ru6.kaspersky-labs.com
  • dnl-ru7.kaspersky-labs.com
  • dnl-ru8.kaspersky-labs.com
  • dnl-ru9.kaspersky-labs.com
  • dnl-us1.kaspersky-labs.com
  • dnl-us10.kaspersky-labs.com
  • dnl-us11.kaspersky-labs.com
  • dnl-us12.kaspersky-labs.com
  • dnl-us13.kaspersky-labs.com
  • dnl-us14.kaspersky-labs.com
  • dnl-us15.kaspersky-labs.com
  • dnl-us2.kaspersky-labs.com
  • dnl-us3.kaspersky-labs.com
  • dnl-us4.kaspersky-labs.com
  • dnl-us5.kaspersky-labs.com
  • dnl-us6.kaspersky-labs.com
  • dnl-us7.kaspersky-labs.com
  • dnl-us8.kaspersky-labs.com
  • dnl-us9.kaspersky-labs.com
  • download.rising.com.cn
  • dswlab.com
  • file.ikaka.com
  • forum.ikaka.com
  • forum.jiangmin.com
  • fw.rising.com.cn
  • go.rising.com.cn
  • help.rising.com.cn
  • kaba.360.cn
  • kpfans.com
  • mcafeefans.com
  • online.jiangmin.com
  • online.rising.com.cn
  • security.symantec.com
  • shadu.baidu.com
  • shadu.duba.net
  • sos.rising.com.cn
  • sucop.com
  • tool.ikaka.com
  • up.duba.net
  • update.ikaka.com
  • update.rising.com.cn
  • www.360.cn
  • www.360Safe.com
  • www.ahn.com.cn
  • www.dswlab.com
  • www.ikaka.com
  • www.kaspersky.com
  • www.kaspersky.com.cn
  • www.kpfans.com
  • www.kztechs.com
  • www.mcafee.com
  • www.pcav.cn
  • www.rising.com.cn
  • www.shudoo.com
  • www.sucop.com
  • www.trendmicro.com.cn
  • www.vrv.com.cn
  • zhidao.ikaka.com


Symantec Security Response encourages all users and administrators to adhere to the following basic security "best practices":

  • Use a firewall to block all incoming connections from the Internet to services that should not be publicly available. By default, you should deny all incoming connections and only allow services you explicitly want to offer to the outside world.
  • Enforce a password policy. Complex passwords make it difficult to crack password files on compromised computers. This helps to prevent or limit damage when a computer is compromised.
  • Ensure that programs and users of the computer use the lowest level of privileges necessary to complete a task. When prompted for a root or UAC password, ensure that the program asking for administration-level access is a legitimate application.
  • Disable AutoPlay to prevent the automatic launching of executable files on network and removable drives, and disconnect the drives when not required. If write access is not required, enable read-only mode if the option is available.
  • Turn off file sharing if not needed. If file sharing is required, use ACLs and password protection to limit access. Disable anonymous access to shared folders. Grant access only to user accounts with strong passwords to folders that must be shared.
  • Turn off and remove unnecessary services. By default, many operating systems install auxiliary services that are not critical. These services are avenues of attack. If they are removed, threats have less avenues of attack.
  • If a threat exploits one or more network services, disable, or block access to, those services until a patch is applied.
  • Always keep your patch levels up-to-date, especially on computers that host public services and are accessible through the firewall, such as HTTP, FTP, mail, and DNS services.
  • Configure your email server to block or remove email that contains file attachments that are commonly used to spread threats, such as .vbs, .bat, .exe, .pif and .scr files.
  • Isolate compromised computers quickly to prevent threats from spreading further. Perform a forensic analysis and restore the computers using trusted media.
  • Train employees not to open attachments unless they are expecting them. Also, do not execute software that is downloaded from the Internet unless it has been scanned for viruses. Simply visiting a compromised Web site can cause infection if certain browser vulnerabilities are not patched.
  • If Bluetooth is not required for mobile devices, it should be turned off. If you require its use, ensure that the device's visibility is set to "Hidden" so that it cannot be scanned by other Bluetooth devices. If device pairing must be used, ensure that all devices are set to "Unauthorized", requiring authorization for each connection request. Do not accept applications that are unsigned or sent from unknown sources.
  • For further information on the terms used in this document, please refer to the Security Response glossary.


The following instructions pertain to all current and recent Symantec antivirus products, including the Symantec AntiVirus and Norton AntiVirus product lines.

  1. Disable System Restore (Windows Me/XP).
  2. Remove all the entries that the risk added to the hosts file.
  3. Update the virus definitions.
  4. Run a full system scan.
  5. Delete any values added to the registry.

For specific details on each of these steps, read the following instructions.

1. To disable System Restore (Windows Me/XP)
If you are running Windows Me or Windows XP, we recommend that you temporarily turn off System Restore. Windows Me/XP uses this feature, which is enabled by default, to restore the files on your computer in case they become damaged. If a virus, worm, or Trojan infects a computer, System Restore may back up the virus, worm, or Trojan on the computer.

Windows prevents outside programs, including antivirus programs, from modifying System Restore. Therefore, antivirus programs or tools cannot remove threats in the System Restore folder. As a result, System Restore has the potential of restoring an infected file on your computer, even after you have cleaned the infected files from all the other locations.

Also, a virus scan may detect a threat in the System Restore folder even though you have removed the threat.

For instructions on how to turn off System Restore, read your Windows documentation, or one of the following articles:

Note: When you are completely finished with the removal procedure and are satisfied that the threat has been removed, reenable System Restore by following the instructions in the aforementioned documents.

For additional information, and an alternative to disabling Windows Me System Restore, see the Microsoft Knowledge Base article: Antivirus Tools Cannot Clean Infected Files in the _Restore Folder (Article ID: Q263455).

2. To remove all the entries that the risk added to the hosts file

  1. Navigate to the following location:

    • Windows 95/98/Me:
    • Windows NT/2000/XP:

    • The location of the hosts file may vary and some computers may not have this file. There may also be multiple copies of this file in different locations. If the file is not located in these folders, search your disk drives for the hosts file, and then complete the following steps for each instance found.
    • %Windir% is a variable that refers to the Windows installation folder. By default, this is C:\Windows (Windows 95/98/Me/XP) or C:\Winnt (Windows NT/2000).

  2. Double-click the hosts file.
  3. If necessary, deselect the "Always use this program to open this program" check box.
  4. Scroll through the list of programs and double-click Notepad.
  5. When the file opens, delete all the entries added by the risk. (See the Technical Details section for a complete list of entries.)
  6. Close Notepad and save your changes when prompted.

3. To update the virus definitions
Symantec Security Response fully tests all the virus definitions for quality assurance before they are posted to our servers. There are two ways to obtain the most recent virus definitions:
  • Running LiveUpdate, which is the easiest way to obtain virus definitions.

    If you use Norton AntiVirus 2006, Symantec AntiVirus Corporate Edition 10.0, or newer products, LiveUpdate definitions are updated daily. These products include newer technology.

    If you use Norton AntiVirus 2005, Symantec AntiVirus Corporate Edition 9.0, or earlier products, LiveUpdate definitions are updated weekly. The exception is major outbreaks, when definitions are updated more often.

  • Downloading the definitions using the Intelligent Updater: The Intelligent Updater virus definitions are posted daily. You should download the definitions from the Symantec Security Response Web site and manually install them.

The latest Intelligent Updater virus definitions can be obtained here: Intelligent Updater virus definitions . For detailed instructions read the document: How to update virus definition files using the Intelligent Updater .

4. To run a full system scan
  1. Start your Symantec antivirus program and make sure that it is configured to scan all the files.

    For Norton AntiVirus consumer products: Read the document: How to configure Norton AntiVirus to scan all files.

    For Symantec AntiVirus Enterprise products: Read the document: How to verify that a Symantec Corporate antivirus product is set to scan all files.

  2. Run a full system scan.
  3. If any files are detected, follow the instructions displayed by your antivirus program.
Important: If you are unable to start your Symantec antivirus product or the product reports that it cannot delete a detected file, you may need to stop the risk from running in order to remove it. To do this, run the scan in Safe mode. For instructions, read the document, How to start the computer in Safe Mode . Once you have restarted in Safe mode, run the scan again.

After the files are deleted, restart the computer in Normal mode and proceed with the next section.

Warning messages may be displayed when the computer is restarted, since the threat may not be fully removed at this point. You can ignore these messages and click OK. These messages will not appear when the computer is restarted after the removal instructions have been fully completed. The messages displayed may be similar to the following:

Title: [FILE PATH]
Message body: Windows cannot find [FILE NAME]. Make sure you typed the name correctly, and then try again. To search for a file, click the Start button, and then click Search.

5. To delete the value from the registry
Important: Symantec strongly recommends that you back up the registry before making any changes to it. Incorrect changes to the registry can result in permanent data loss or corrupted files. Modify the specified subkeys only. For instructions refer to the document: How to make a backup of the Windows registry .
  1. Click Start > Run.
  2. Type regedit
  3. Click OK.

    Note: If the registry editor fails to open the threat may have modified the registry to prevent access to the registry editor. Security Response has developed a tool to resolve this problem. Download and run this tool, and then continue with the removal.

  4. Navigate to and delete the following registry subkeys:

    • HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\compbatc
    • HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\compbatcDrv
    • HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\[8 NUMBERS]

  5. Restore the following registry entries to their previous values, if required

    • HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\SafeBoot\Network
    • HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\SafeBoot\Minimal

  6. Restore the following registry entries to their previous values, if required:

    • HKEY_LOCAL_MACHINE\SOFTWARE\360Safe\safemon\"UDiskAccess" = "0"
    • HKEY_LOCAL_MACHINE\SOFTWARE\360Safe\safemon\"ExecAccess" = "0"
    • HKEY_LOCAL_MACHINE\SOFTWARE\360Safe\safemon\"IEProtAccess" = "0"
    • HKEY_LOCAL_MACHINE\SOFTWARE\360Safe\safemon\"LeakAccess" = "0"
    • HKEY_LOCAL_MACHINE\SOFTWARE\360Safe\safemon\"MonAccess" = "0"
    • HKEY_LOCAL_MACHINE\SOFTWARE\360Safe\safemon\"SiteAccess" = "0"
    • HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Run\"360Safetray"
    • HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Run\"360Safebox"
    • HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Run\"360Antiarp"
    • HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Run\"runeip"
    • HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Run\"Iparmor"

  7. Exit the Registry Editor.

    Note: If the risk creates or modifies registry subkeys or entries under HKEY_CURRENT_USER, it is possible that it created them for every user on the compromised computer. To ensure that all registry subkeys or entries are removed or restored, log on using each user account and check for any HKEY_CURRENT_USER items listed above.

Writeup By: Elia Florio