W32.Opaserv.Worm

NOTE: Due to a decreased rate of submissions, Symantec Security Response has downgraded this threat from Category 3 to Category 2 as of June 13, 2003. W32.Opaserv.Worm is a network-aware worm that attempts to replicate across open network shares. It copies itself to the remote computer as a file named Scrsvr.exe. This worm also attempts to download updates from www.opasoft.com, although the site may have already been shut down. Indicators of infection include: The existence of the files Scrsin.dat and Scrsout.dat in the root of drive C. This indicates a local infection (that is, the worm was executed on the local computer). The existence of the Tmp.ini file in the root of drive C. This indicates a remote infection (that is, the computer was infected by a remote host). The registry key HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\Current Version\Run contains the string value ScrSvr or ScrSvrOld, which is set to c:\tmp.ini. NOTE: If you are on a network, or have a full time connection to the Internet such as DSL or Cable modem, you must disconnect the computer from the network and the Internet before attempting to remove this worm. If you have shared files or folders, these must be disabled. When you have finished the removal procedure, if you decide to reenable file sharing, Symantec suggests that you do not share the root of drive C. Share specific folders instead. These shares must be password-protected with a secure password. Do not use a blank password. Also, before doing so, if you are using Windows 95/98/Me, you must download and install the Microsoft patch from http://www.microsoft.com/technet/security/bulletin/MS00-072.asp
Removal tool link: http://securityresponse.symantec.com/avcenter/venc/data/w32.opaserv.worm.removal.tool.html

Also Known As:	W32/Opaserv.worm [McAfee], W32/Opaserv-A [Sophos], Win32.Opaserv [CA], WORM_OPASOFT.A [Trend], Worm.Win32.Opasoft [AVP]
Type:	Worm
Infection Length:	28,672 bytes
Systems Affected:	Windows 95, Windows 98, Windows NT, Windows 2000, Windows XP, Windows Me
Systems Not Affected:	Windows 3.x, Microsoft IIS, Macintosh, UNIX, Linux
CVE References:	CVE-2000-0979

Virus Definitions (LiveUpdate™ Weekly) September 30, 2002 Virus Definitions (Intelligent Updater) September 30, 2002

Wild Number of infections: More than 1000 Number of sites: More than 10 Geographical distribution: High Threat containment: Moderate Removal: Moderate

Threat Metrics Wild: Low Damage: Low Distribution: Medium

Distribution

• Shared drives: Attempts to spread to non-password protected shares

When W32.Opaserv.Worm runs, it does the following:

It checks for the value

ScrSvrOld

in the registry key

HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Run

If the value exists, the worm deletes the file that the ScrSvrOld points to.

If the ScrSvrOld value does not exist, then the worm determines whether the value

ScrSvr

exists in the registry key

HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Run

If the value does not exist, the worm adds the value

ScrSvr %windir%\ScrSvr.exe

to that registry key.

Next it checks whether it is being run as the file %windir%\ScrSvr.exe. If it is not, it copies itself to that file name and adds the value

ScrSvrOld  <original worm name>

to the registry key

HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Run

NOTE: %windir% is a variable. The worm locates the Windows installation folder (by default this is C:\Windows or C:\Winnt) and uses that as a destination folder.

After the worm checks the registry values and the location from which the worm is executing, the worm checks to make sure that only one instance of the worm is running in memory by creating a mutex with the name ScrSvr31415.

If it is not already executing, the worm registers itself as a process under Windows 95/98/Me. Under Windows NT/2000/XP it elevates the priority of the worm process.

The worm then inventories the network looking for "C\" shares. For each share that it finds, it copies itself to C\Windows\Scrsvr.exe.

The worm uses a security vulnerability in Microsoft Windows 95/98/Me. It sends single character passwords to network shares to get access to Windows 95/98/Me file shares without knowing the entire password assigned to the shares. The affected systems include,

• Microsoft Windows 95
• Microsoft Windows 98
• Microsoft Windows 98 Second Edition
• Microsoft Windows Me

• The worm modifies the file C:\Windows\Win.ini before it copies itself as %windir%\ScrSvr.exe. Therefore, Symantec antivirus products will find and delete %windir%\ScrSvr.exe after the system has been altered, but not before it modifies the Win.ini file. As a result, when you restart the computer, you may see a message that ScrSvr.exe cannot be found. To fix this, remove the line that the worm added.
• The worm is apparently coded to add this line to the Win.ini:
  
  run= c:\tmp.ini
  
  However, in actual infections or detections, the worm is adding the line run= c:\ScrSvr.exe.

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.

IMPORTANT - READ THIS FIRST:

• This worm uses a security vulnerability in Microsoft Windows 95/98/Me. It sends single character passwords to network shares to get access to Windows 95/98/Me file shares without knowing the entire password assigned to the shares. The affected systems include Windows 95, 98, and Me.
  
  A patch for computers running these operating systems can be found at http://www.microsoft.com/technet/security/bulletin/MS00-072.asp. If you have not already done so, you must obtain and install the patch to prevent future infections.
  
• If you are on a network, or have a full time connection to the Internet such as DSL or Cable modem, you must disconnect the computer from the network and the Internet. Disable sharing before reconnecting computers to the network or to the internet. Because this worm spreads by using shared folders on networked computers, to ensure that the worm does not reinfect the computer after it has been removed, you must remove all shares, clean all computers on the network, patch all systems, and update definitions on all computers before you reconnect to the network or reenable shares.
• For instructions on how to do this,see your Windows documentation or the document How to configure shared Windows folders for maximum network protection.
• If you are removing an infection on a network, make sure any shares are disabled before doing so.

1. Disconnect from the network if connected.
2. Update the virus definitions.
3. Run a full system scan, and delete all files that are detected as W32.Opaserv.Worm
4. Delete the values
   
   ScrSvr %windir%\ScrSvr.exe
   
   and
   
   ScrSvrOld <original worm name>
   
   from the registry key
   
   HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Run
   
5. (Windows 95/98/Me only ) Delete the line
   
   run= c:\ScrSvr.exe
   
   or
   
   run= c:\tmp.ini
   
   from the C:\Windows\Win.ini.
   

• Do not skip this step. You must disconnect from the network before attempting to remove this worm.
• For additional information on file sharing, read your Windows documentation or the document How to configure shared Windows folders for maximum network protection.
• When you have finished the removal procedure, if you decide to reenable file sharing, Symantec suggests that you do not share the root of drive C. Share specific folders instead. These shares must be password-protected with a secure password. Do not use a blank password.
  
  Also, before doing so, if you are using Windows 95/98/Me, you must download and install the Microsoft patch from
  
  http://www.microsoft.com/technet/security/bulletin/MS00-072.asp

• Run LiveUpdate, which is the easiest way to obtain virus definitions. These virus definitions 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 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.

1. Start your Symantec antivirus program, and make sure that it is configured to scan all files.
   • Norton AntiVirus consumer products: Read the document How to configure Norton AntiVirus to scan all files.
   • Symantec enterprise antivirus products: Read the document How to verify 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.Opaserv.Worm, click Delete.

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 the key
   
   HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Run
   
4. In the right pane, delete these value:
   
   ScrSvr %windir%\ScrSvr.exe
   
   ScrSvrOld <original worm name>
   
5. Exit the Registry Editor.

1. Click Start, and click Run.
2. Type the following, and then click OK.
   
   edit c:\windows\win.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 an entry similar to either (or both) of the following:
   
   run= c:\ScrSvr.exe
   
   run= c:\tmp.ini
   
4. Select the entire line. Be sure that you have not selected any other text in the file, and then press Delete.
5. Click File, and click Save.
6. Click File, and click Exit.

Additional information:


If you are on a network, have a full time connection to the Internet such as DSL or Cable modem, or often leave a dial-up connection open for extended periods, we strongly recommend the installation of a firewall for additional protection. For information on Symantec firewall products, go to:

http://www.symantec.com/product/

If you are using a Norton AntiVirus consumer product, also read the document How to prevent reinfections of W32.Opaserv.Worm.

Revision History:

• June 13, 2003: Downgraded from Category 3 to Category 2 based on decreased rate of submissions.
• September 30, 2002: Upgraded from Category 2 to Category 3 based on increased rate of submissions.

Write-up by: Douglas Knowles and Peter Ferrie