W32.Tuoba.Trojan

SUMMARY

W32.Tuoba.Trojan uses an Internet Explorer exploit to add a Web server to the Intranet zone and to redirect network traffic to that server.

For information on the exploit, refer to http://www.securityfocus.com/bid/9658.

Protection

• Virus Definitions (LiveUpdate™ Weekly) March 15, 2004
• Virus Definitions (Intelligent Updater) March 15, 2004

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: Low

Distribution

• Distribution Level: Low

TECHNICAL DETAILS

W32.Tuoba.Trojan is installed by visiting a malicious Web page. The Web page uses an Internet Explorer exploit to execute the Content.php file, which is a malicious CHM file.

Content.php contains three files:

• Index.html, which uses an Internet Explorer exploit to download the file, Run.exe to C:Program FilesEn1857.exe, and then execute it. This file is detected as XMLid.Exploit.
• Htm2chm_explorer, which is not malicious.
• Htm2chm_about, which is not malicious.
  

When it is executed, Run.exe does the following:

1. Adds 213.159.118.226 to the local Intranet zone in Internet Explorer by modifying the values in the registry key:
   
   HKEY_USERS.DEFAULTSoftwareMicrosoftWindowsCurrentVersion
   Internet SettingsoneMapRangesRange1
   
   
2. Redirects requests to certain Web sites to the address 213.159.118.226. It does this by overwriting the Hosts file. These lines that are added to the file appear to mainly target Web sites, which adware automatically opens:
   

213.159.118.226 1-se.com
213.159.118.226 58q.com
213.159.118.226 aifind.cc
213.159.118.226 aifind.info
213.159.118.226 allneedsearch.com
213.159.118.226 approvedlinks.com
213.159.118.226 auto.ie.searchforge.com
213.159.118.226 awebfind.biz
213.159.118.226 best.royalsearch.net
213.159.118.226 cracks.am
213.159.118.226 default-homepage-network.com
213.159.118.226 find.microgirls.com
213.159.118.226 find4u.net
213.159.118.226 freshvideogals.com
213.159.118.226 i-lookup.com
213.159.118.226 ie-search.com
213.159.118.226 in.webcounter.cc
213.159.118.226 itseasy.us
213.159.118.226 just.find-itnow.com
213.159.118.226 link.startmake.com
213.159.118.226 mysearchnow.com
213.159.118.226 nativehardcore.com
213.159.118.226 qwertysearch123.biz
213.159.118.226 search.ieplugin.com
213.159.118.226 search.psn.cn
213.159.118.226 searchbar.findthewebsiteyouneed.com
213.159.118.226 searchcentrix.com
213.159.118.226 searchmyrequest.com
213.159.118.226 super-spider.com
213.159.118.226 t.rack.cc
213.159.118.226 teen-biz.com
213.159.118.226 teenhqpics.com
213.159.118.226 tits.hardcore4ever.net
213.159.118.226 webcoolsearch.com
213.159.118.226 wmmse.com
213.159.118.226 www.008i.com
213.159.118.226 www.2fastsearch.net
213.159.118.226 www.8095.com
213.159.118.226 www.alfa-search.com
213.159.118.226 www.boredlife.com
213.159.118.226 www.couldnotfind.com
213.159.118.226 www.cracks.am
213.159.118.226 www.daum.net
213.159.118.226 www.dreamwiz.com
213.159.118.226 www.find-itnow.com
213.159.118.226 www.find-itnow.com
213.159.118.226 www.find4u.net
213.159.118.226 www.firstbookmark.com
213.159.118.226 www.gajai.com
213.159.118.226 www.hand-book.com
213.159.118.226 www.hao123.com
213.159.118.226 www.hotsearchbox.com
213.159.118.226 www.hotwebsearch.com
213.159.118.226 www.hugesearch.net
213.159.118.226 www.iquicksearch.com
213.159.118.226 www.lookfor.cc
213.159.118.226 www.maxxxhosters.com
213.159.118.226 www.naver.com
213.159.118.226 www.nkvd.us
213.159.118.226 www.novafuck.com
213.159.118.226 www.ohcorea.com
213.159.118.226 www.omega-search.com
213.159.118.226 www.onet.pl
213.159.118.226 www.power-search.info
213.159.118.226 www.rightfinder.net
213.159.118.226 www.search-1.net
213.159.118.226 www.search-and-go.com
213.159.118.226 www.search-dot.com
213.159.118.226 www.search-space.com
213.159.118.226 www.searchforge.com
213.159.118.226 www.searching-the-net.com
213.159.118.226 www.searchv.com
213.159.118.226 www.searchxl.com
213.159.118.226 www.seznam.cz
213.159.118.226 www.slotch.com
213.159.118.226 www.spidersearch.com
213.159.118.226 www.startium.com
213.159.118.226 www.therealsearch.com
213.159.118.226 www.ttjj.com
213.159.118.226 www.viewpornkey.com
213.159.118.226 www.wazzupnet.com
213.159.118.226 www.websearch.com
213.159.118.226 www.windowws.cc
213.159.118.226 www.xgmm.com
213.159.118.226 xwebsearch.biz
213.159.118.226 yourbookmarks.ws

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. Delete the value that was added to the registry.
4. Run a full system scan and delete all the files detected as W32.Tuoba.Trojan.
5. Delete the entries that were added to the hosts file.
   

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"

---

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.

---

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. Deleting the value from the registry

---

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.

---

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_USERS.DEFAULTSoftwareMicrosoftWindowsCurrentVersion
   Internet SettingsoneMapRangesRange1
   
   
4. In the right pane, either delete the values or restore them to their original values.
   
   
5. Exit the Registry Editor.
   
   
6. Restart the computer.

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 infected with W32.Tuoba.Trojan, click Delete.
   
   

5. Removing the lines from the Hosts file

---

Note: The location of the Hosts file may vary and some computers may not have this file.

For example, if the file exists in Windows 98, it will usually be in C:Windows, and is located in the C:WINNTsystem32driversetc folder within Windows 2000. There may also be multiple copies of this file in different locations.

---

Follow the instructions for your operating system:

• Windows 98/Me/2000
  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:
     
     hosts
     
     
  4. Click Find Now or Search Now.
  5. For each one that you find, right-click it, and then click "Open With."
  6. Deselect the "Always use this program to open this program" check box.
  7. Scroll through the list of programs and double-click Notepad.
  8. Delete any lines begin with:
     
     213.159.118.226
     
     
  9. Close Notepad and save your changes when prompted.
     
     
• Windows XP
  1. Click Start, and then click Search.
  2. Click All files and folders.
  3. In the "All or part of the file name" box, type:
     
     hosts
     
     
  4. Verify that "Look in" is set to "Local Hard Drives" or to (C:).
  5. Click "More advanced options."
  6. Check "Search system folders."
  7. Check "Search subfolders."
  8. Click Search.
  9. Click Find Now or Search Now.
  10. For each one that you find, right-click it, and then click "Open With."
  11. Deselect the "Always use this program to open this program" check box.
  12. Scroll through the list of programs and double-click Notepad.
  13. Delete any lines begin with:
      
      213.159.118.226
      
      
  14. Close Notepad and save your changes when prompted.