Trojan.Trunlow

SUMMARY

Trojan.Trunlow is Trojan horse that attempts to steal passwords, including cached Windows passwords, protected storage passwords, and passwords for dial-up accounts and mail accounts.

This Trojan is usually distributed through links that are hidden in Web pages or pop-up windows, and may exploit Internet Explorer vulnerabilities to download and execute files.

Protection

• Virus Definitions (LiveUpdate™ Weekly) April 1, 2004
• Virus Definitions (Intelligent Updater) April 1, 2004

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: Medium
• Releases Confidential Info: Steals passwords and uploads them to a public HTTP server.
• Compromises Security Settings: Attempts to terminate antivirus processes.

Distribution

• Distribution Level: Low

TECHNICAL DETAILS

Trojan.Trunlow consists of the following components:

HTML component
This is a piece of html code that downloads and executes the VBScript component. This code may be added to pages on legitimate Web sites whose security has been compromised. Some versions use the exploit described in Bloodhound.Exploit.6.


VBScript component
There are many versions of this script. It may be found with one of the following filenames:

• frame2.sas
• Dc50.vbs
• a4d22.vbs

In general, this component does the following:

1. Attempts to terminate services associated with antivirus software. Known variants have targeted the following:
   
   • AVG6 Service
   • AVSync Manager
   • FW Configuration Interpreter
   • Kerio Personal Firewall
   • McAfee.com McShield
   • McAfee.com VirusScan Online Realtime Engine
   • McShield
   • NaV alert
   • Norton AntiVirus Auto Protect Service
   • Norton AntiVirus Client
   • PC-cillin PersonalFirewall
   • Sophos Anti-Virus
   • Sweep for Windows NT Network
   • Sweep for Windows NT Update
   • Symantec AntiVirus Client
   • Symantec Event Manager
   • Trend NT Realtime Service
   • TrueVector Internet Monitor
   • avsync manager
   • defwatch
   • nav auto-protect
   • norton program scheduler
     
     
2. Downloads other files, including password-recovery software, from an FTP server or an HTTP server.
   
   
3. Uploads stolen passwords and other system information to an FTP server, or to an ASP script on an HTTP server.
   
   

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   Note: Some variants use an exploit in ADODB stream objects in Microsoft Internet Explorer to download and execute files.

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Updater
The VBScript component downloads an executable, usually named winupdate.exe, which may be used to download updates of the Trojan.

This component does the following:

1. Attempts to download and execute a file from a Web server.
   
   
2. Copies itself as %Windir%Winupdate.exe.
   
   

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   Note: %Windir% is a variable. The Trojan horse locates the Windows installation folder (by default, this is C:Windows or C:Winnt) and copies itself to that location.

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3. Adds the value:
   
   "Microsoft Eventlog"="%Windir%Winupdate.exe"
   
   to the registry key:
   
   HKEY_CURRENT_USERSOFTWAREMicrosoftWindowsCurrentVersionRun
   
   so that the Trojan starts when Windows starts.

Nonmalicious files
The VBScript component may download these files. Because they are not malicious, Symantec antivirus products do not detect them.

These files include the following:

Password-recovery software:

• cucu.dll
• cucu.exe
• m.exe
• dp.exe
• mp.exe
  
  

Two .html files used to format the stolen information before uploading it:

• top
• butt

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. Run a full system scan and delete all the files detected as Trojan.Trunlow.
4. Delete the value that was added to the registry.
   

For specific 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"

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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.

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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 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. 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.Trunlow, click Delete.

4. To delete the value from the registry

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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.

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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_LOCAL_MACHINESOFTWAREMicrosoftWindowsCurrentVersionRun
   
   
4. In the right pane, delete the value:
   
   "Microsoft Eventlog"="%Windir%Winupdate.exe"
   
   
5. Exit the Registry Editor.