W32.Korgo.A

SUMMARY

W32.Korgo.A is a worm that attempts to exploit the Microsoft LSASS Windows vulnerability, described in Microsoft Security Bulletin MS04-011. The worm also listens on TCP ports 113, 2041, and 3067, and allows unauthorized access to the infected computer.

Note: Virus definitions dated prior to May 23, 2004 detect this threat as Bloodhound.Packed.

Protection

• Virus Definitions (LiveUpdate™ Weekly) May 26, 2004
• Virus Definitions (Intelligent Updater) May 23, 2004

Threat Assessment

Wild

• Wild Level: Low
• Number of Infections: 50 - 999
• Number of Sites: 3 - 9
• Geographical Distribution: Low
• Threat Containment: Easy
• Removal: Moderate

Damage

• Damage Level: Medium
• Degrades Performance: May impact on system performance.

Distribution

• Distribution Level: Medium
• Ports: TCP ports 113, 2041, 3067, 6667, 445.
• Target of Infection: Unpatched machines vulnerable to the Microsoft LSASS Windows exploit.

TECHNICAL DETAILS

When W32.Korgo.A is executed, it performs the following actions:

1. Deletes the file, go.exe, from the folder where the worm was executed.
   
   
2. Creates the mutexes "r10," "u2," and "uterm5" to ensure that only one instance of the worm can be executed on the computer.
   
   
3. Looks for the value:
   
   "WinUpdate"
   
   in the registry key:
   
   HKEY_LOCAL_MACHINESOFTWAREMicrosoftWindowsCurrentVersionRun
   
   
   • If the "WinUpdate" value does not exist, the worm will:
     
     1. Add the value:
        
        "Server"="1"
        
        to the registry key:
        
        HKEY_LOCAL_MACHINESOFTWAREMicrosoftWireless
        
        
     2. Copy itself as %System%<random filename>.exe.
        
        

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        Note: %System% is a variable. The worm locates the System folder and copies itself to that location. By default, this is C:WindowsSystem (Windows 95/98/Me), C:WinntSystem32 (Windows NT/2000), or C:WindowsSystem32 (Windows XP).

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     3. Add the value:
        
        "WinUpdate"="%System%<random filename>.exe"
        
        to the registry key:
        
        HKEY_LOCAL_MACHINESOFTWAREMicrosoftWindowsCurrentVersionRun
        
        
     4. Launch <random filename>.exe, and then end the current process.
        
        
   • If the "WinUpdate" value exists, but the path of the file is different than the worm, it will:
     
     
     1. Copy itself as %System%<random.filename>.exe.
        
        

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        Note: %System% is a variable. The worm locates the System folder and copies itself to that location. By default, this is C:WindowsSystem (Windows 95/98/Me), C:WinntSystem32 (Windows NT/2000), or C:WindowsSystem32 (Windows XP).

        ---

        
        
     2. Add the value:
        
        "WinUpdate"="%System%<random.filename>.exe"
        
        to the registry key:
        
        HKEY_LOCAL_MACHINESOFTWAREMicrosoftWindowsCurrentVersionRun
        
        
     3. Launch <random.filename>.exe, and then end the current process.
        
        
   • If the "WinUpdate" value exists and the value matches the path of the worm, it will delete the value:
     
     "Server"
     
     from the registry key:
     
     HKEY_LOCAL_MACHINESOFTWAREMicrosoftWireless
     
     
4. Listens on the following TCP ports:
   
   • 113
   • 3067
   • 2041
     
     

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     Note: The worm attempts to listens on a random port. Due to bugs in the code, it will always listen on TCP port 2041. The worm will send itself through this port.

     ---

     
     
5. Attempts to connect to one of the following IRC servers on TCP port 6667:
   
   • moscow-advokat.ru
   • graz.at.eu.undernet.org
   • flanders.be.eu.undernet.org
   • caen.fr.eu.undernet.org
   • brussels.be.eu.undernet.org
   • los-angeles.ca.us.undernet.org
   • washington.dc.us.undernet.org
   • london.uk.eu.undernet.org
   • lia.zanet.net
   • gaspode.zanet.org.za
   • irc.kar.net
     
     
6. Starts a thread to exploit the LSASS Windows vulnerability on TCP port 445 (described in Microsoft Security Bulletin MS04-011) against random IP addresses. If successful, the remote computer may attempt to connect to the infected computer and download the worm.
   
   
7. Starts an infinite loop that prevents the computer from shutting down.

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. Reverse the changes that were added to the registry, and then restart the computer.
4. Run a full system scan and delete all the files detected as W32.Korgo.A.
   

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:

• "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. 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 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. To reverse the changes that were made to the registry, restart computer

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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 > 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 the value:
   
   "WinUpdate"="%System%<random.filename>.exe"
   
   
5. Navigate to the key:
   
   HKEY_LOCAL_MACHINESOFTWAREMicrosoftWireless
   
   
6. In the right pane, delete the value:
   
   "Server"="1"
   
   
7. Exit the Registry Editor.
   
   
8. Restart the computer.

4. To scan for and delete 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 infected with W32.Korgo.A, click Delete.
   
   

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   Note: If your Symantec antivirus product reports that it cannot delete an infected file, Windows may be using the file. To fix 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. When that is done, restart the computer in Normal mode.

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