W32.Tendoolf

SUMMARY

W32.Tendoolf is a variant of Backdoor.Subseven, which appears to be able to spread through email. The email message has the following characteristics:

Subject: Thoughts...
Message: I just found this program, and, i dont know why... but it reminded me of you. check it out.
Attachment: Cute.exe

The mailing routine has not been successfully reproduced in a laboratory environment.

Behavior

Symptoms

Transmission

Protection

• Virus Definitions (LiveUpdate™ Weekly) May 8, 2002
• Virus Definitions (Intelligent Updater) May 2, 2002

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: Sends mail to all recipients in the Outlook Address Book.
• Large Scale E-mailing: Sends mail to all recipients in the Outlook Address Book.
• Compromises Security Settings: Allows unauthorized access to the computer.

Distribution

• Distribution Level: Low
• Subject of Email: Thoughts...
• Name of Attachment: Cute.exe
• Size of Attachment: 228,352 bytes or 608,768 bytes

TECHNICAL DETAILS

When W32.Tendoolf is executed, it does the following:

It copies itself to C:WindowsKernel32.exe.

It adds the value

Windows      C:WINDOWSKERNEL32.EXE

to the following registry keys:

HKEY_LOCAL_MACHINESOFTWAREMicrosoftWindows
CurrentVersionRun

HKEY_LOCAL_MACHINESOFTWAREMicrosoftWindows
CurrentVersionRunServices

It then changes a line in the System.ini file from

shell=Explorer.exe

to

shell=explorer.exe C:WINDOWSKERNEL32.EXE

It also changes a line in the Win.ini file from

load=

to

load=C:WINDOWSKERNEL32.EXE

W32.Tendoolf appears to be coded to have the ability to spread through email. The email message has the following characteristics:

Subject: Thoughts...
Message: I just found this program, and, i dont know why... but it reminded me of you. check it out.
Attachment: Cute.exe

The mailing routine has not been successfully reproduced in a laboratory environment.

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

Delete files that are detected as W32.Tendoolf, remove the values that it added to the registry, and (Windows 95/98/Me only) remove the text that it added to the two Windows startup files.

To delete files that are detected as W32.Tendoolf:

1. Obtain the most recent virus definitions. There are two ways to do this:
   • Run LiveUpdate. LiveUpdate is the easiest way to obtain virus definitions. These virus definitions have undergone full quality assurance testing by Symantec Security Response and are posted to the LiveUpdate servers one time 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 have undergone full quality assurance testing by Symantec Security Response. They 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.
     
2. 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.
3. Run a full system scan.
4. Delete all files that are detected as W32.Tendoolf.

To remove the values that W32.Tendoolf added to the registry:

CAUTION: Symantec strongly recommends that you back up the registry before you make any changes to it. Incorrect changes to the registry can result in permanent data loss or corrupted files. Modify only the keys that are specified. Read the document How to make a backup of the Windows registry for instructions.

1. Click Start, and click Run. The Run dialog box appears.
2. Type regedit and then click OK. The Registry Editor opens.
3. Navigate to each of the following keys:
   
   HKEY_LOCAL_MACHINESOFTWAREMicrosoftWindows
   CurrentVersionRun
   
   HKEY_LOCAL_MACHINESOFTWAREMicrosoftWindows
   CurrentVersionRunServices
   
4. In the right pane, delete the following value:
   
   Windows      C:WINDOWSKERNEL32.EXE
   
5. Click Registry, and click Exit.

To remove the text that W32.Tendoolf added to the Windows startup files:

NOTE: This is only necessary on Windows 95/98/Me.

1. Click Start, and click Run.
2. Type the following, and then click OK.
   
   edit c:windowswin.ini
   
   The MS-DOS Editor opens.
   
   NOTE: If Windows is installed in a different location, make the appropriate path substitution.
   
3. In the [windows] section of the file, look for an entry similar to the following:
   
   load=C:WINDOWSKERNEL32.EXE
   
4. Select the entire line. Be sure that you have not selected any other text, and then press Delete.
5. Click File, and click Save.
6. Click File, and click Exit.
7. Click Start, and click Run.
8. Type the following, and then click OK.
   
   edit c:windowssystem.ini
   
   The MS-DOS Editor opens.
   
   NOTE: If Windows is installed in a different location, make the appropriate path substitution.
   
9. In the [boot] section, locate the following line:
   
   shell=explorer.exe C:WINDOWSKERNEL32.EXE
   
10. Delete the text to the right of shell=explorer.exe so that the line consists of only:
    
    shell=explorer.exe
    
11. Click File, and click Save.
12. Click File, and click Exit.