Trojan.Trunlow

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_USER\SOFTWARE\Microsoft\Windows\CurrentVersion\Run
   
   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":

• Use a firewall to block all incoming connections from the Internet to services that should not be publicly available. By default, you should deny all incoming connections and only allow services you explicitly want to offer to the outside world.
• 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.
• Ensure that programs and users of the computer use the lowest level of privileges necessary to complete a task. When prompted for a root or UAC password, ensure that the program asking for administration-level access is a legitimate application.
• Disable AutoPlay to prevent the automatic launching of executable files on network and removable drives, and disconnect the drives when not required. If write access is not required, enable read-only mode if the option is available.
• Turn off file sharing if not needed. If file sharing is required, use ACLs and password protection to limit access. Disable anonymous access to shared folders. Grant access only to user accounts with strong passwords to folders that must be shared.
• Turn off and remove unnecessary services. By default, many operating systems install auxiliary services that are not critical. These services are avenues of attack. If they are removed, threats have less avenues of attack.
• If a 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.
• Configure your email server to block or remove email that contains file attachments that are commonly used to spread threats, such as .vbs, .bat, .exe, .pif and .scr files.
• Isolate compromised computers quickly to prevent threats from spreading further. 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.
• If Bluetooth is not required for mobile devices, it should be turned off. If you require its use, ensure that the device's visibility is set to "Hidden" so that it cannot be scanned by other Bluetooth devices. If device pairing must be used, ensure that all devices are set to "Unauthorized", requiring authorization for each connection request. Do not accept applications that are unsigned or sent from unknown sources.
• For further information on the terms used in this document, please refer to the Security Response glossary.

Summary