W32.HLLW.Cebe

SUMMARY

W32.HLLW.Cebe is a worm that spreads through the KaZaA and Imesh file-sharing networks. This worm has backdoor capabilities and starts an FTP server on an infected computer.

W32.HLLW.Cebe is written in the Delphi programming language.

Protection

• Virus Definitions (LiveUpdate™ Weekly) November 17, 2003
• Virus Definitions (Intelligent Updater) November 13, 2003

Threat Assessment

Wild

• Wild Level: Low
• Number of Infections: 0 - 49
• Number of Sites: 0 - 2
• Geographical Distribution: Low
• Threat Containment: Easy
• Removal: Easy

Damage

• Damage Level: Low
• Payload Trigger: N/A
• Payload: N/A
• Large Scale E-mailing: N/A
• Deletes Files: N/A
• Modifies Files: N/A
• Releases Confidential Info: N/A
• Degrades Performance: N/A
• Causes System Instability: N/A
• Compromises Security Settings: Starts an FTP server. May have additional backdoor capabilities.

Distribution

• Distribution Level: Medium
• Subject of Email: N/A
• Name of Attachment: N/A
• Size of Attachment: N/A
• Ports: FTP server listens on TCP port 21.
• Shared Drives: Kazaa and IMesh shared folders.
• Target of Infection: N/A
• Time Stamp of Attachment: N/A

TECHNICAL DETAILS

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Note: The information in this document applies to one variant of the worm. W32.HLLW.Cebe appears to be configurable so that some details may vary from what is described here. Configurable parameters include file names, a registry key, and a server port.

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1. Copies itself to %Windir%Sistry.exe.
   
   

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   Note: %Windir% is a variable. The worm locates the Windows installation folder (by default, this is C:Windows or C:Winnt) and copies itself to that location.

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2. Adds the value:
   
   "sistry"="%Windir%sistry.exe"
   
   to the registry key:
   
   HKEY_LOCAL_MACHINESoftwareMicrosoftWindowsCurrentVersionRun
   
   so that the worm runs when you start Windows.
   
   
3. Queries the registry keys:
   
   HKEY_LOCAL_MACHINESoftwareKaZaaLocalContent
   HKEY_LOCAL_MACHINESoftwareiMeshClientLocalContent
   
   to find the shared folders that KaZaA and IMesh use. The worm copies itself to these shared folders as "Half Life CD crack.exe."
   
   
4. May copy itself to the hard-coded folder, C:WindowsSystemIosubsys, and set this location to be a KaZaA or IMesh shared folder.
   
   
5. Starts an FTP server, listening on port 21.
   

Recommendations

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

• Turn off and remove unneeded services. By default, many operating systems install auxiliary services that are not critical, such as an FTP server, telnet, and a Web server. These services are avenues of attack. If they are removed, blended threats have less avenues of attack and you have fewer services to maintain through patch updates.
• If a blended 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 (for example, all Windows-based computers should have the current Service Pack installed.). Additionally, please apply any security updates that are mentioned in this writeup, in trusted Security Bulletins, or on vendor Web sites.
• 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.
• Configure your email server to block or remove email that contains file attachments that are commonly used to spread viruses, such as .vbs, .bat, .exe, .pif and .scr files.
• Isolate infected computers quickly to prevent further compromising your organization. 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.

REMOVAL

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. Update the virus definitions.
3. Restart the computer in Safe mode or VGA mode.
4. Run a full system scan and delete all the files detected as W32.HLLW.Cebe.
5. Reverse the change made to the registry.
6. Check the configuration of KaZaA or IMesh, if you use these programs.
   

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

1. Disabling 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"

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

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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. Updating 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 the Virus Definitions (LiveUpdate).
• Downloading the definitions using the Intelligent Updater: The Intelligent Updater virus definitions are posted on U.S. business days (Monday through Friday). 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 the Virus Definitions (Intelligent Updater).
  
  The Intelligent Updater virus definitions are available: Read "How to update virus definition files using the Intelligent Updater" for detailed instructions.

3. Restarting the computer in Safe mode or VGA mode
Shut down the computer and turn off the power. Wait for at least 30 seconds, and then restart the computer in Safe mode or VGA mode.

• For Windows 95, 98, Me, 2000, or XP users, restart the computer in Safe mode. For instructions, read the document, "How to start the computer in Safe Mode."
• For Windows NT 4 users, restart the computer in VGA mode.

4. Scanning for and deleting the infected files

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 as W32.HLLW.Cebe, note the path and file names, and then click Delete.

5. Reversing the change made to the registry

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WARNING: 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 keys only. Read the document, "How to make a backup of the Windows registry," for instructions.

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1. Click Start, and then click Run. (The Run dialog box appears.)
   
2. Type regedit
   
   Then click OK. (The Registry Editor opens.)
   
   
3. Navigate to the key:
   
   HKEY_LOCAL_MACHINESoftwareMicrosoftWindowsCurrentVersionRun
   
   
4. In the right pane, delete any values that refer to the files noted in step 4.
   For example:
   
   "sistry"="C:WINDOWSsistry.exe"
   
   
5. Exit the Registry Editor.

6. Checking the configuration of KaZaA or IMesh software
This worm may modify the configuration of KaZaA and IMesh by adding new shared folders. If you use these programs, check the programs configuration to ensure that new shared folders have not been added.