W32.Remabl.Worm

SUMMARY

W32.Remabl.Worm is a worm that attempts to spread through the local network and may have backdoor capabilities. The existence of the file shambl3r.exe is an indication of a possible infection.

Protection

• Virus Definitions (LiveUpdate™ Weekly) October 22, 2003
• Virus Definitions (Intelligent Updater) October 16, 2003

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: Medium
• Shared Drives: Attempts to connect to remote systems to copy itself to the StartUp folder.

TECHNICAL DETAILS

W32.Remable.Worm consists of one .dll file and two .exe files. The file names are usually the following:

• Shambl3r.exe: Self-extracting zip file contains many python scripts.
• Sys.exe: Symantec Security Response has not received this file yet.
• Python23.dll: legitimate dll file for Python scripts.

When W32.Remable.Worm is executed, it does the following:

1. Obtains network information by using the ipconfig command and then upload the information to a predetermined FTP site.
   
   
2. Creates %Windows%Cnf.bat, which will run Sys.exe. This may allow the author of the program to access command.com or cmd.exe on the infected computer from a remote computer by using a predetermined username and password.
   

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   Note: %Windir% is a variable. The worm 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. Add the following lines to the [windows] section of the Win.ini file on Windows 95/98/Me computers:
   
   run=%Windows%cnf.bat
   load=%Widnows%shambl3r.exe
   
   
4. Adds the values:
   • "shambl3r"="C:\%Windows%cnf.bat"
   • "shambl3r2"="C:\%Windows%shambl3r.exe"
   • "shambl3r3"="C:\%Windows%shambl3r.exe"
   • "shambl3r4"="C:\%Windows%shambl3r.exe"
   • "shambl3r5"="C:\%Windows%shambl3r.exe"
   • "shambl3r6"="C:\%Windows%shambl3r.exe"
   • "shambl3r7"="C:\%Windows%shambl3r.exe"
   • "shambl3r8"="C:\%Windows%shambl3r.exe"
   • "shambl3r9"="C:\%Windows%shambl3r.exe"
   • "shambl3r10"="C:\%Windows%shambl3r.exe"
   • "shambl3r11"="C:\%Windows%shambl3r.exe"
     
     to the registry key
     
     HKEY_LOCAL_MACHINESOFTWAREMicrosoftWindowsCurrentVersionRun
     
     on Windows NT/2000/XP computers.
     
     
5. Creates a random IP addresses each time the worm is executed.
   
   
6. Pings the IP addresses and if a response is received, tries to connect following folders:
   • X:Documents and SettingsAll UsersMen・InicioProgramasInicio
   • X:Documents and SettingsAll UsersStart MenuProgramsStartup
   • X:Dokumente und EinstellungenAll UsersStart MenuProgramsStartup
   • X:Documenti e ImpostazioniAll UsersStart MenuProgramsStartup
   • X:WINNTProfilesAll UsersStart MenuProgramsStartup
   • X:WINNTProfilesAll UsersMen・InicioProgramasInicio
   • X:WINDOWSStart MenuProgramsStartup
   • X:WINDOWSMen・InicioProgramasinicio
   • X:WINDOWSAll UsersStart MenuProgramsStartup
   • X:WINDOWSAll UsersMen・InicioProgramasInicio
   • X:Documents and SettingsAll UsersMenu InicioProgramasInicio
   • X:Documents and SettingsAll UsersMenu InicioProgramasstartup
   • X:Documents and SettingsAll UsersMenu IniciarProgramasInicializar
   • X:Dokumente und einstellungenall usersStartmen・programmeautostart
   • X:Documents and settingsAll usersMenu avvioProgrammiEsecuzione automatica
   • X:Documents and SettingsAll UsersMenu IniciarProgramasstartup
   • X:Documents and SettingsAll UsersMenu IniciarProgramasInicio
   • X:WINDOWSAll UsersStartmenueProgrammeAutostart
   • X:WINDOWSStartmenueProgrammeAutostart
   • X:WindowsMenu IniciarprogramasIniciar
   • X:WindowsMenu D駑arrerProgrammesD駑arrage
   • X:WindowsStartmen・ProgrammeAutostart
   • X:Windowsmenu avvioprogrammiesecuzione automatica
   • X:Documents and settingsAll usersStart-menyProgramAutostart
   • %sStart MenuProgramsStartup
   • %sMen・InicioProgramasinicio
   • %sAll UsersStart MenuProgramsStartup
   • %sAll UsersMen・InicioProgramasInicio
   • %sProfilesAll UsersStart MenuProgramsStartup
   • %sProfilesAll UsersMen・InicioProgramasInicio
     
     
7. Copies Shaml3r.exe, Sys.exe and Python23.dll to the folders above.
   
   
8. Attempts to connect to other computers within the same network range as the randomly generated IP address.
   
   For example, if the randomly generated IP address is A.B.C.D, the worm will then attempt to connect to all computers with an IP address that begins with A.B.x.x.

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 W32.Ramabl.Worm
4. Delete the value that was added to the registry.
5. Edit the Win.ini 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"
  

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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. 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 W32.Remabl.Worm, 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. On the Windows taskbar, click Start > Run.
   
2. In the Run dialog box, type regedit
   
3. Click OK.
   
4. In the Resgistry Editor, navigate to the key:
   
   HKEY_LOCAL_MACHINESOFTWAREMicrosoftWindowsCurrentVersionRun
   
   
5. In the right pane, delete the values:
   • "shambl3r"="C:\%Windows%cnf.bat"
   • "shambl3r2"="C:\%Windows%shambl3r.exe"
   • "shambl3r3"="C:\%Windows%shambl3r.exe"
   • "shambl3r4"="C:\%Windows%shambl3r.exe"
   • "shambl3r5"="C:\%Windows%shambl3r.exe"
   • "shambl3r6"="C:\%Windows%shambl3r.exe"
   • "shambl3r7"="C:\%Windows%shambl3r.exe"
   • "shambl3r8"="C:\%Windows%shambl3r.exe"
   • "shambl3r9"="C:\%Windows%shambl3r.exe"
   • "shambl3r10"="C:\%Windows%shambl3r.exe"
   • "shambl3r11"="C:\%Windows%shambl3r.exe"
     
     
6. Exit the Registry Editor.

5. Editing the Win.ini 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 Win.ini 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 Win.ini file and delete it. The Win.ini file will be regenerated when you save your changes to it in step f.
        
2. Click Start > Run.
3. Type the following, and then click OK.
   
   edit c:windowswin.ini
   
   (The MS-DOS Editor opens.)
   
   

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   Note: If Windows is installed in a different location, make the appropriate path substitution.

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4. In the [Windows] section of the file, look for lines similar to:
   
   run=%Windows%cnf.bat
   load=%Widnows%shambl3r.exe
   
5. If these lines exist, delete everything to the right of run= and load=.
6. Click File > Save.
7. Click File > Exit.