Trojan.Vundo

SUMMARY

Trojan.Vundo is a component of an adware program that downloads and displays pop-up advertisements. It is known to be installed by visiting a Web site link contained in a spammed email.

Note: Virus definitions released prior to November 20, 2004 may detect this threat as Adware.VirtuMonde.

Protection

• Virus Definitions (LiveUpdate™ Weekly) November 23, 2004
• Virus Definitions (Intelligent Updater) November 20, 2004

Threat Assessment

Wild

• Wild Level: Medium
• Number of Infections: 50 - 999
• Number of Sites: More than 10
• Geographical Distribution: Medium
• Threat Containment: Easy
• Removal: Difficult

Damage

• Damage Level: Medium
• Degrades Performance: Degrades virtual menory and runs unauthorized processes.
• Compromises Security Settings: Download a file from the internet

Distribution

• Distribution Level: Low

TECHNICAL DETAILS

Trojan.Vundo consists of four components:

1. HTML code that exploits the Microsoft Internet Explorer Malformed IFRAME Remote Buffer Overflow Vulnerability (described in the Microsoft Security Bulletin MS04-040).
2. A downloader component.
3. Adware.
4. A DLL module that the adware installed.
   
   

The HTML code exploits the Microsoft Internet Explorer Malformed IFRAME Remote Buffer Overflow Vulnerability (described in the Microsoft Security Bulletin MS04-040), and attempts to download and execute the file, C:la.exe, from the address 83.149.86.132. This is the downloader component of the Trojan.

Once this Trojan is executed on the infected computer, it performs the following actions:

1. Creates a .exe file with a file name that it is constructed from the following strings:
   
   • abr
   • av
   • anti
   • ac
   • acc
   • ad
   • ap
   • as
   • bin
   • bas
   • bak
   • cab
   • cat
   • cmd
   • com
   • cr
   • c
   • drv
   • db
   • disk
   • dll
   • dns
   • dos
   • doc
   • dvd
   • eula
   • exp
   • fax
   • font
   • ftp
   • hard
   • iis
   • img
   • inet
   • info
   • ip
   • java
   • kb
   • key
   • lib
   • log
   • main
   • ms
   • mc
   • mfc
   • mp3
   • msvc
   • net
   • nut
   • odbc
   • ole
   • pc
   • ps
   • play
   • ras
   • reg
   • run
   • sys
   • srv
   • svr
   • svc
   • s
   • tapi
   • tcp
   • task
   • un
   • url
   • util
   • vb
   • vga
   • vss
   • xml
   • wave
   • web
   • w
   • win
   • wms
     
     
     Saves and executes the above file in any of the following directories:
     
   • %Windir%addins
   • %Windir%AppPatch
   • %Windir%assembly
   • %Windir%Config
   • %Windir%Cursors
   • %Windir%Driver Cache
   • %Windir%Drivers
   • %Windir%Fonts
   • %Windir%Help
   • %Windir%inf
   • %Windir%java
   • %Windir%Microsoft.NET
   • %Windir%msagent
   • %Windir%Registration
   • %Windir%epair
   • %Windir%security
   • %Windir%ServicePackFiles
   • %Windir%Speech
   • %Windir%system
   • %Windir%system32
   • %Windir%Tasks
   • %Windir%Web
   • %Windir%Windows Update Setup Files
   • %Windir%Microsoft
     
     Note: %Windir% is a variable that refers to the Windows installation folder. By default, this is C:Windows or C:Winnt.
     
     
2. Deletes the value:
   
   "*MS Setup"
   
   from the registry key:
   
   HKEY_CURRENT_USERSoftwareMicrosoftWindowsCurrentVersionRunOnce
   
   
3. Adds the value:
   
   "*WinLogon" = "[Trojan full path file name] ren time:[random number]"
   
   to the registry key:
   
   HKEY_CURRENT_USERSoftwareMicrosoftWindowsCurrentVersionRunOnce
   
   
4. Creates the following registry entry:
   
   HKEY_CURRENT_USERSoftwareMicrosoftInternet ExplorerMainActive State
   
   
5. Attempts to download and execute a file from the IP address 62.4.84.41.
   
   The retrieved file is an adware module with an embedded DLL component.
   
   
6. Appears to store the URL list and may attempt to send HTTP request to one of the following IP addresses:
   
   • 62.4.84.53
   • 62.4.84.56
     
     
7. Drops the embedded DLL as %Temp%[reversed Trojan file name].dat.
   
   
8. Injects the embedded DLL into the address space of several running processes, and each process executed after the threat begins running.
   
   
9. Creates the following temporary files, which are not malicious:
   
   • [reversed Trojan file name].bak1
   • [reversed Trojan file name].bak2
   • [reversed Trojan file name].ini
     
     
10. Adds the value:
    
    "*[Trojan file name]" = "[Trojan full path file name] rerun"
    
    to the registry key:
    
    HKEY_LOCAL_MACHINESoftwareMicrosoftWindowsCurrentVersionRunOnce
    
    
11. Adds the value:
    
    "Default value]" = "{02F96FB7-8AF6-439B-B7BA-2F952F9E4800}"
    
    to the registry keys:
    
    HKEY_LOCAL_MACHINESOFTWAREClassesATLEvents.ATLEventsCLSID
    HKEY_LOCAL_MACHINESOFTWAREClassesATLEvents.ATLEvents.1CLSID
    
    
12. Creates the following registry entries:
    
    HKEY_LOCAL_MACHINESOFTWAREClassesCLSID{02F96FB7-8AF6-439B-B7BA-2F952F9E4800}
    HKEY_LOCAL_MACHINESOFTWAREMicrosoftWindowsCurrentVersionExplorer
    Browser Helper Objects{02F96FB7-8AF6-439B-B7BA-2F952F9E4800}HKEY_LOCAL_MACHINESOFTWAREClassesCLSID{2353FCBC-012D-487B-8BF3-865C0929FBEB} HKEY_LOCAL_MACHINESOFTWAREClassesATLDistrib.ATLDistribCLSID
    HKEY_LOCAL_MACHINESOFTWAREClassesATLDistrib.ATLDistrib.1CLSID
    HKEY_USERSS-1-5-21-2068663838-1736639611-1443527720-500SoftwareMicrosoftWindows
    CurrentVersionExtStats{2353FCBC-012D-487B-8BF3-865C0929FBEB}
    HKEY_LOCAL_MACHINESOFTWAREClassesCLSID{22E85F2A-4A67-4835-B2C3-C575FE4EC322}
    HKEY_LOCAL_MACHINESOFTWAREClassesADOUsefulNet.ADOUsefulNet
    HKEY_LOCAL_MACHINESOFTWAREClassesADOUsefulNet.ADOUsefulNet.1
    HKEY_LOCAL_MACHINESOFTWAREMicrosoftWindowsCurrentVersionExplorerBrowser Helper Objects{22E85F2A-4A67-4835-B2C3-C575FE4EC322}
    HKEY_LOCAL_MACHINESOFTWAREMicrosoftWindowsCurrentVersionExplorerBrowser Helper Objects{DE8BDE42-16D9-4CCC-9F4F-1C3167B82F60}
    HKEY_CLASSES_ROOTCLSID{DE8BDE42-16D9-4CCC-9F4F-1C3167B82F60}
    HKEY_LOCAL_MACHINESOFTWAREClassesDPCUpdater.DPCUpdater
    HKEY_LOCAL_MACHINESOFTWAREClassesDPCUpdater.DPCUpdater.1
    
    
13. Displays advertisements on the infected computer.
    
    
14. Restarts the adware component if the Trojan detects that the adware component has stopped running.
    
    
15. After a restart, the Trojan will be executed with "rerun" parameter, (see step 10). If the Trojan is executed with "rerun" parameter, it adds the value:
    
    "*[Trojan file name]" = "[Trojan full path file name]"
    
    to the registry key:
    
    HKEY_LOCAL_MACHINESOFTWAREMicrosoftWindowsCurrentVersionRun
    
    
16. Degrades the performance of the computer by decreasing the amount of virtual memory available. This is a result of the Trojan exploiting the Microsoft Internet Explorer Malformed IFRAME Remote Buffer Overflow Vulnerability (as described in the Microsoft Security Bulletin MS04-040).

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

Removal using the Removal Tool
Symantec Security Response has developed a removal tool to clean the infections of Trojan.Vundo. This is the preferred method in most cases.

Manual 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 in Safe mode or VGA mode.
4. Run a full system scan and delete all the files detected as Trojan.Vundo.
5. Reverse the changes made to the registry.
   

For 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"

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. 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 daily. 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 restart the computer in Safe mode or VGA mode

Shut down the computer and turn off the power. Wait for at least 30 seconds, and then restart the computer in Safe mode with Command Prompt or VGA mode.

• For Windows 95, 98, Me, 2000, or XP users, restart the computer in Safe mode. For instructions, read the document, "How to start the computer in Safe Mode."
• For Windows NT 4 users, restart the computer in VGA mode.
  

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 Trojan.Vundo, click Delete.

5. To reverse the changes made to the registry


Important: 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 > Run.
2. Type regedit
   
   Then click OK.
   
   
3. Navigate to the keys:
   
   HKEY_LOCAL_MACHINESOFTWAREClassesATLEvents.ATLEventsCLSID
   HKEY_LOCAL_MACHINESOFTWAREClassesATLEvents.ATLEvents.1CLSID
   
   
4. In the right pane, delete the value:
   
   "[Default value]" = "{02F96FB7-8AF6-439B-B7BA-2F952F9E4800}"
   
   
5. Navigate to the key:
   
   HKEY_CURRENT_USERSoftwareMicrosoftWindowsCurrentVersionRunonce
   
   
6. If it exists, in the right pane, delete the value:
   
   "*WinLogon = "[Trojan full path file name] ren time:[random number]"
   
   
7. Navigate to the key:
   
   HKEY_LOCAL_MACHINESOFTWAREMicrosoftWindowsCurrentVersionRunOnce
   
   
8. If it exists, in the right pane, delete the value:
   
   "*[Trojan file name]" = "[Trojan full path file name] rerun"
   
   
9. Navigate to the key:
   
   HKEY_LOCAL_MACHINESoftwareMicrosoftWindowsCurrentVersionRun
   
   
10. If it exists, in the right pane, delete the value:
    
    "*[Trojan file name]" = "[Trojan full path file name]"
    
    
11. Navigate to and delete the following registry entries:
    
    HKEY_CURRENT_USERSoftwareMicrosoftInternet ExplorerMainActiveState
    HKEY_LOCAL_MACHINESOFTWAREClassesCLSID{02F96FB7-8AF6-439B-B7BA-2F952F9E4800}
    HKEY_LOCAL_MACHINESOFTWAREMicrosoftWindowsCurrentVersionExplorer
    Browser Helper Objects{02F96FB7-8AF6-439B-B7BA-2F952F9E4800}
    HKEY_LOCAL_MACHINESOFTWAREClassesCLSID{2353FCBC-012D-487B-8BF3-865C0929FBEB} HKEY_LOCAL_MACHINESOFTWAREClassesATLDistrib.ATLDistribCLSID
    HKEY_LOCAL_MACHINESOFTWAREClassesATLDistrib.ATLDistrib.1CLSID
    HKEY_USERSS-1-5-21-2068663838-1736639611-1443527720-500SoftwareMicrosoftWindows
    CurrentVersionExtStats{2353FCBC-012D-487B-8BF3-865C0929FBEB}
    HKEY_LOCAL_MACHINESOFTWAREClassesCLSID{22E85F2A-4A67-4835-B2C3-C575FE4EC322}
    HKEY_LOCAL_MACHINESOFTWAREClassesADOUsefulNet.ADOUsefulNet
    HKEY_LOCAL_MACHINESOFTWAREClassesADOUsefulNet.ADOUsefulNet.1
    HKEY_LOCAL_MACHINESOFTWAREMicrosoftWindowsCurrentVersionExplorerBrowser Helper Objects{22E85F2A-4A67-4835-B2C3-C575FE4EC322}
    HKEY_LOCAL_MACHINESOFTWAREMicrosoftWindowsCurrentVersionExplorerBrowser Helper Objects{DE8BDE42-16D9-4CCC-9F4F-1C3167B82F60}
    HKEY_CLASSES_ROOTCLSID{DE8BDE42-16D9-4CCC-9F4F-1C3167B82F60}
    HKEY_LOCAL_MACHINESOFTWAREClassesDPCUpdater.DPCUpdater
    HKEY_LOCAL_MACHINESOFTWAREClassesDPCUpdater.DPCUpdater.1
    
    
12. Exit the Registry Editor.
    
    
13. Restart the computer in Normal mode. For instructions, read the section on returning to Normal mode in the document, "How to start the computer in Safe Mode."