Discovered: August 24, 2005
Updated: February 13, 2007 12:42:59 PM
Systems Affected: Windows
W32.Zotob.K is a worm that opens a back door and exploits the Microsoft Windows Plug and Play Buffer Overflow Vulnerability (as described in Microsoft Security Bulletin MS05-039 ) on TCP port 445.
Note: While computers running Windows 95/98/Me/NT4/XP operating systems cannot be infected remotely, it is possible they could be infected if W32.Zotob.K is executed locally (although this is an unlikely occurrence). Vulnerable Windows 2000 computers could then be infected by the compromised computer.
Antivirus Protection Dates
- Initial Rapid Release version August 24, 2005
- Latest Rapid Release version May 07, 2019 revision 006
- Initial Daily Certified version August 24, 2005
- Latest Daily Certified version May 07, 2019 revision 008
- Initial Weekly Certified release date August 24, 2005
Click here for a more detailed description of Rapid Release and Daily Certified virus definitions.
When executed, W32.Zotob.K performs the following actions:
- Creates the following mutex so that only one copy of the worm runs on the compromised computer at one time:
- Copies itself as the following file:
Note: %System% is a variable that refers to the System folder. By default this is C:\Windows\System (Windows 95/98/Me), C:\Winnt\System32 (Windows NT/2000), or C:\Windows\System32 (Windows XP).
- Adds the value:
"wintnl.exe" = "wintnl.exe"
to the registry subkey:
so that it runs every time Windows starts.
- May fail to operate correctly if it detects it is not connected to a network or if the computer's IP address is non-routable.
- Connects to the following IRC server on TCP port 6664 to listen for IRC commands:
- Allows the attacker to use IRC commands to perform the following actions:
- Download and execute files from the IRC server.
- Delete the worm from the compromised computer.
- Opens UDP port 69 for TFTP.
- Sends packets to randomly generated IP addresses, based on the IP address of the compromised computer. The generated IP addresses then use the first 2 octets of the compromised computer and randomly generates values for the third and fourth octets. The worm will begin to generate entirely random IP addresses after 32 failures on local IP addresses or after 512 failures, if it was successful at least once.
- Attempts to exploit the Microsoft Windows Plug and Play Buffer Overflow Vulnerability (as described in Microsoft Security Bulletin MS05-039) on TCP port 445.
- If successful, the exploit code will open a back door using TCP Port 8172 on the remote computer.
- Sends the file %Temp%\[NUMBER].bat to the target computer via the back door. This file contains a TFTP script that will download a copy of the worm from the compromised computer.
- [NUMBER] represents several random numbers from 0 - 9.
- %Temp% is a variable that refers to the Windows temporary folder. By default, this is C:\Windows\TEMP (Windows 95/98/Me/XP) or C:\WINNT\Temp (Windows NT/2000).
- Saves the file as %Windir%\a[NUMBER].exe on the target computer and executes it.
Note: %Windir% is a variable that refers to the Windows installation folder. By default, this is C:\Windows or C:\Winnt.
- Ends the following processes:
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.
- Disable System Restore (Windows Me/XP).
- Update the virus definitions.
- Run a full system scan and delete all the files detected.
- Delete any values added to the registry.
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:
- How to disable or enable Windows Me System Restore
- How to turn off or turn on Windows XP System Restore
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 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: These virus definitions are posted to the LiveUpdate servers once each week (usually on Wednesdays), unless there is a major virus outbreak. To determine whether definitions for this threat are available by LiveUpdate, refer to Virus Definitions (LiveUpdate).
- 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. To determine whether definitions for this threat are available by the Intelligent Updater, refer to Virus Definitions (Intelligent Updater).
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.
3. To scan for and delete the infected files
- 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.
- Run a full system scan.
- If any files are detected, click Delete.
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.
4. 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.
- Click Start > Run.
- Type regedit
- 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.
- Navigate to the subkey:
- In the right pane, delete the value:
"wintnl.exe" = "wintnl.exe"
- Exit the Registry Editor.
Writeup By: Kaoru Hayashi