W95.CIH.1106

SUMMARY

This is a variant of the W95.CIH virus. It is a Windows 95/98/Me memory-resident virus that infects executable files. This variant triggers the CIH payload on the second day of every month. For more information please read the W95.CIH.1049 write-up.

NOTE: Virus definitions dated prior to November 20, 2002, may detect this as W95.CIH.1094 or Bloodhound.W32.EP.

Protection

• Virus Definitions (LiveUpdate™ Weekly) November 20, 2002
• Virus Definitions (Intelligent Updater) November 15, 2002

TECHNICAL DETAILS

The payload for W95.CIH.1106 executes on the second day of every month. For technical detail information and information about the payload please read the W95.CIH.1049 write-up.

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

NOTES:

• These instructions are for all current and recent Symantec antivirus products, including the Symantec AntiVirus and Norton AntiVirus product lines.
• If the payload has executed, it is likely that you will have to restore the contents of the hard drive from backup.
• If the virus is resident in memory, you will have to remove it using the DOS scanner. Instructions for doing this with the Norton AntiVirus product line are provided in this document.

1. Update the virus definitions.
2. Run a full system scan, and delete all files that are detected as W95.CIH.1106. If this is not possible because the virus is resident in memory, remove the virus using the DOS scanner.

For details on how to do this, read the following instructions.

To update the virus definitions:
All virus definitions receive full quality assurance testing by Symantec Security Response before being posted to our servers. There are two ways to obtain the most recent virus definitions:

• Run LiveUpdate, which is the easiest way to obtain virus definitions. These virus definitions are posted to the LiveUpdate servers once each week (usually Wednesdays) unless there is a major virus outbreak. To determine whether definitions for this threat are available by LiveUpdate, look at the Virus Definitions (LiveUpdate) line at the top of this write-up.
• Download the definitions using the Intelligent Updater. Intelligent Updater virus definitions are posted on U.S. business days (Monday through Friday). They must be downloaded from the Symantec Security Response Web site and installed manually. To determine whether definitions for this threat are available by the Intelligent Updater, look at the Virus Definitions (Intelligent Updater) line at the top of this write-up.
  
  Intelligent Updater virus definitions are available here. For detailed instructions on how to download and install the Intelligent Updater virus definitions from the Symantec Security Response Web site, click here.

To scan for and delete the infected files:

1. Start your Symantec antivirus program, and make sure that it is configured to scan all files.
   • Norton AntiVirus consumer products: Read the document How to configure Norton AntiVirus to scan all files.
   • Symantec enterprise antivirus products: Read the document How to verify 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 W95.CIH.1106, click Delete.

To remove W95.CIH.1106 using the DOS scanner:
There instructions apply to the Norton AntiVirus consumer product line.

Do one of the following:

• If your computer can boot from the CD-ROM drive and you are using Norton AntiVirus 2001 or later:
  1. Place the Norton AntiVirus CD into the CD-ROM drive, and restart the computer.
  2. When the menu appears, proceed to scan and repair viruses.
  3. After the scan has finished, remove the CD from the CD-ROM drive, and restart the computer.
  4. Start Norton AntiVirus (NAV), and make sure that NAV is configured to scan all files. For instructions on how to do this, read the document How to configure Norton AntiVirus to scan all files.
  5. Run a full system scan.
  6. If any files are detected as infected by W95.CIH.1106, click Delete. Restore these files from backup.
• If your computer cannot boot from the CD-ROM drive or if you are using Norton AntiVirus 2000 or earlier:
  1. Install Norton AntiVirus (NAV) on an uninfected computer.
  2. Run LiveUpdate, and then run a full system scan.
  3. On the NAV toolbar, click Rescue.
  4. Follow the prompts to create a Basic Rescue set.
  5. Take the completed Basic Rescue set to the infected computer, and insert the "Basic Rescue Boot Disk" into the floppy disk drive. Restart the computer.
  6. When the Rescue Disk window appears, use the arrow keys on the keyboard to select Norton AntiVirus.
  7. Edit the command line at the bottom of the window to read
     
     navdx /a /b+ /m+ /repair /cfg:a /log:c: vreplog.txt
     
     and then press Enter.
  8. After the scan has finished, repeat steps 6 through 8 again; this time edit the command line to read
     
     navdx /a /b+ /m+ /delete /cfg:a /log:c: vdellog.txt
     
     and then press Enter.
  9. After the scan has finished, the removal process is complete. Remove all disks from the disk drives, and restart the computer.
  10. Start NAV, and make sure that it is configured to scan all files. For instructions on how to do this, read the document How to configure Norton AntiVirus to scan all files.
  11. Run a full system scan.
  12. If any files are detected as infected by W95.CIH.1106, click Delete. Restored these files from backup.