W32.Nimda.R

SUMMARY

W32.Nimda.R is a limited version of W32.Nimda.A@mm. This variant infects Portable Executable (PE) files and creates network shares for all the drives. Further, the virus adds the user Guest under the groups, Guests and Administrators. This gives the guest account Administrative privileges.

Behavior

Symptoms

Transmission

Protection

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

Threat Assessment

Wild

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

Damage

• Damage Level: Medium
• Payload: Adds the user Guest under the groups, Guests and Administrators. This gives the guest account Administrative privileges.

Distribution

• Distribution Level: Low
• Target of Infection: PE files.

TECHNICAL DETAILS

For detailed information, refer to the W32.Nimda.A@mm writeup.

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.
   
   NOTE: When your computer restarts, it is likely that the infected files will be found. We recommend that you attempt to repair them. Quarantine any files that cannot be repaired.
   
   
4. Run a full system scan and repair all the files detected as W32.Nimda.R. If the files cannot be repaired, delete them, and if necessary, replace them from a clean backup.
5. Restore Riched20.dll from a backup, or from the Microsoft Windows or Office .cab files, if necessary.
6. Remove the unnecessary shares and delete the guest account from the Administrators group, if applicable.

For specific 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"

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
Shut down the computer and turn off the power. Wait 30 seconds, and then normally restart the computer.


4. Scanning for and repairing the infected files

1. Start your Symantec antivirus software 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.Nimda.R, click Repair. If the files cannot be repaired, delete them, and if necessary, replace them from a clean backup.

5. Restoring Riched20.dll
If you see errors when you start programs such as Microsoft Word, or if the programs do not start, extract the Riched20.dll file. (As an alternative, you can re-install the operating system and the affected programs.)

Refer to the instructions for your operating system.

NOTE: These instructions are provided for your convenience and will work on most computers. For additional information on extracting files, including other Windows files that may have been damaged, read one of the following:

• If you are using Microsoft Outlook 2002 or Microsoft Office 2002, there is an easier way to do this. These programs can replace the Riched20.dll file if you first rename it.
• For instructions on how to do this, read:
  • Microsoft Knowledge Base article, "OL2002: Outlook Stops Responding with Riched20.dll Error Messages," Article ID: Q291651. 
  • Microsoft Knowledge Base article, "HOW TO: Extract Original Compressed Windows Files," Article ID: Q129605.
  • "How to extract files in Windows 98 and Windows Me."
    

Windows 95/98
Use the Extract command at a DOS prompt. Perform the following steps, using the instructions for your operating system.

NOTES:
• You will need a Windows 98/Me startup disk. (If you are using Windows 95, you will still need one that was created on a Windows 98/Me computer). For instructions on how to create one, see the document, "How to create a Windows Startup disk."
• Have available the Windows installation CD.
• When typing the command, substitute the appropriate drive letter for your CD-ROM drive for the letter x. For example, if you are using Windows 98, and the CD-ROM drive is drive D, then you would type:
  
  extract /a d:win98win98_28.cab riched20.dll /L c:windowssystem


• If Windows is installed in a folder other than C:Windows, then substitute the appropriate path or folder name in the last part of the command that refers to the Windows folder.
• For detailed instructions on using the Extract command, see the Microsoft document, "How to Extract Original Compressed Windows Files," Article ID: Q129605.
• As a somewhat easier alternative to the following procedure, if you are using Windows 98, you can use the System File Checker to restore the file. For information on how to do this, see your Windows documentation.

1. Shut down the computer and turn off the power. Once the computer is off, insert the Windows 98/Me Startup disk in the floppy disk drive and restart the computer. At the menu, select Start with CD-ROM support.
   
   
2. Type the command that applies to your operating system:
   • If you are using Windows 98, then type the following and press Enter:
     
     extract /a d:win98win98_28.cab riched20.dll /L c:windowssystem
     
     
   • If you are using Windows 95, then type the following and press Enter:
     
     extract /a win95_10.cab riched20.dll /L c:windowssystem

NOTE: If you see an any error message, then repeat step 2, making sure that you typed the correct command (and exactly as shown) for your operating system. Otherwise, type exit, and then press Enter.

Windows NT 4.0

1. Make sure that Windows is configured to show all files.
2. Search for, and then delete all the Riched20.dll files.
3. Re-apply the most recent service pack. The service pack will replace the file with a new copy.
4. If, after replacing the Riched20.dll file, programs such as Microsoft Word or Office no longer run, or you see error messages when they start, you may need to re-install Microsoft Office.

Windows 2000
If you are using Windows 2000, a built-in program will find and replace missing or corrupt system files. To replace the corrupted Riched20.dll, follow these steps:

1. Make sure System File Checker is enabled:
   1. Click Start, and then click Run.
   2. Type cmd, and then click OK.
   3. Type the following and then press Enter:
      
      sfc /enable
      
      
   4. Type exit, and then press Enter.
      
      
2. Make sure that Windows is set to show all files:
   1. Start Windows Explorer.
   2. Click the Tools menu, and then click Folder options.
   3. Click the View tab.
   4. Uncheck "Hide file extensions for known file types."
   5. Uncheck "Hide protected operating system files," and under the "Hidden files" folder, click "Show hidden files and folders."
   6. Click Apply, and then click OK.
      
      
3. Search for Riched20.dll:
   1. Click Start, point to Find or Search, and then click Files or Folders.
   2. Make sure that "Look in" is set to (C) and that Include subfolders is checked.
   3. In the "Named" or "Search for..." box, type or copy and paste the following filename:
      
      riched20.dll
      
      
   4. Click Find Now or Search Now.
   5. Delete the displayed files.
      
      
4. Restart the computer.
5. System File Checker will replace any missing Riched20.dll files. If, after replacing the Riched20.dll file, programs such as Microsoft Word or Office no longer run, or you see error messages when they start, you may need to re-install Microsoft Office.

6. Removing shares and accounts
The following is intended for Network Administrators or IT Professionals:

• If the Guest account is unexpectedly in the Administrators group, then remove it.
• If the Guest account is not required, then disable it.
• Delete the shares that are not required.