W32.Sinista

SUMMARY

W32.Sinista is a Trojan horse that allows unauthorized access to the computer. It is written using the Microsoft Visual Basic (VB) programming language.

Protection

• Virus Definitions (LiveUpdate™ Weekly) July 15, 2002
• Virus Definitions (Intelligent Updater) July 15, 2002

TECHNICAL DETAILS

When W32.Sinista runs, it does the following:

It copies itself as:

• C:\%system%RunDLL8.exe
• C:\%windir%Matrix.scr
• C:WindowsAll usersStart menuProgramsStartupNav.exe (only under Windows95/98/Me)
• A:<A very long and crude file name>.exe

NOTES:

• %windir% is a variable. The worm locates the Windows main installation folder (by default this is C:Windows or C:Winnt) and copies itself to that location.
• %system% is a variable. The worm locates the System folder. By default this is C:WindowsSystem (Windows 95/98/Me), C:WinntSystem32 (Windows NT/2000), or C:WindowsSystem32 (Windows XP), and copies itself to that location.

Next, it creates the subkey

current versionun

in the registry key

HKEY_LOCAL_MACHINESoftwareMicrosoftWindows

and adds the value

RunDLL C:\%System%RunDLL8.exe

to this subkey. Due to the bug in the Trojan program, C:\%System%RunDLL8.exe is not executed when you restart Windows.

To the following registry key the Trojan also adds a value that refers to its copy on drive A:

HKEY_CLASSES_ROOTinifileshellopencommand

The worm then adds the following line to [windows] section of the Win.ini file:

[windows]
run=C:Windowsmatrix.scr

This causes the Trojan to run when you start Windows.

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

NOTE: These instructions are for all current and recent Symantec antivirus products, including the Symantec AntiVirus and Norton AntiVirus product lines.

1. Update the virus definitions, run a full system scan, and delete all files that are detected as W32.Sinista.
2. Delete the registry key
   
   HKEY_LOCAL_MACHINESoftwareMicrosoftWindowscurrent version
   
3. Restore HKEY_CLASSES_ROOTinifileshellopencommand to its installed setting.
4. Remove the line
   
   run=C:Windowsmatrix.scr
   
   from the Win.ini file in Windows 95/98/Me-based computers.

For details on how to do this, read the following instructions.

To scan for and delete the infected files:

1. Obtain the most recent virus definitions. There are two ways to do this:
   • Run LiveUpdate. LiveUpdate is the easiest way to obtain virus definitions. These virus definitions have undergone full quality assurance testing by Symantec Security Response and are posted to the LiveUpdate servers one time each week (usually Wednesdays) unless there is a major virus outbreak. To determine whether definitions for this threat are available by LiveUpdate, look at the Virus Definitions (LiveUpdate) line at the top of this write-up.
   • Download the definitions using the Intelligent Updater. Intelligent Updater virus definitions have undergone full quality assurance testing by Symantec Security Response. They are posted on U.S. business days (Monday through Friday). They must be downloaded from the Symantec Security Response Web site and installed manually. To determine whether definitions for this threat are available by the Intelligent Updater, look at the Virus Definitions (Intelligent Updater) line at the top of this write-up.
     
     Intelligent Updater virus definitions are available here. For detailed instructions on how to download and install the Intelligent Updater virus definitions from the Symantec Security Response Web site, click here.
     
2. Start Norton AntiVirus (NAV), and make sure that NAV is configured to scan all files.
   • NAV Consumer products: Read the document How to configure Norton AntiVirus to scan all files.
   • NAV Enterprise products: Read the document How to verify a Symantec Corporate antivirus product is set to scan All Files.
3. Run a full system scan.
4. Delete all files that are detected as W32.Sinista.

To remove the keys or values that the Trojan added to the registry:

CAUTION: Symantec strongly recommends that you back up the registry before you make any changes to it. Incorrect changes to the registry can result in permanent data loss or corrupted files. Modify only the keys that are specified. Read the document How to make a backup of the Windows registry for instructions.

1. Click Start, and click Run. The Run dialog box appears.
2. Type regedit and then click OK. The Registry Editor opens.
3. Navigate to and select the following key:
   
   HKEY_LOCAL_MACHINESoftwareMicrosoftWindowscurrent version
   
   CAUTION: Make sure that you select the current version subkey that has a space between the words current and version. Do not select the key in which currentversion is a single word.
   
4. Delete the current version subkey.
5. Navigate to the following key:
   
   HKEY_CLASSES_ROOTinifileshellopencommand
   
6. In the right pane, double-click (Default).
7. Remove any text that the worm added, leaving the original value.
   
   NOTE: The original value will vary depending on the version of Windows and the installation path. Two common values are shown here. If you are not sure what to do, contact a qualified computer consultant.
   
   Windows 2000 typical value
   %SystemRoot%System32NOTEPAD.EXE %1
   
   Windows 98 typical value
   C:WindowsNOTEPAD.EXE %1
   
8. Exit the Registry Editor.

To remove the line that the Trojan added to the Win.ini file:
This is necessary only if you are running Windows 95/98/Me.

NOTE: (For Windows Me users only) Due to the file-protection process in Windows Me, a backup copy of the file that you are about to edit exists in the C:WindowsRecent folder. Symantec recommends that you delete this file before you continue with the steps in this section. To do this using Windows Explorer, go to C:WindowsRecent, and in the right pane select the Win.ini file and delete it. It will be regenerated as a copy of the file that you are about to edit when you save your changes to that file.

1. Click Start, and click Run.
2. Type the following, and then click OK.
   
   edit c:windowswin.ini
   
   The MS-DOS Editor opens.
   
   NOTE: If Windows is installed in a different location, make the appropriate path substitution.
   
3. In the [windows] section of the file, look for the following line:
   
   run=C:Windowsmatrix.scr
   
4. Select the entire line. Be sure that you have not selected any other text, and then press Delete.
5. Click File, and click Save.
6. Click File, and click Exit.