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Discovered: April 21, 2004
Updated: February 13, 2007 12:21:42 PM
Also Known As: W32/Blaster-G [Sophos], WORM_MSBLAST.I [Trend], W32/Blaster.worm.k [McAfee]
Type: Worm
Systems Affected: Windows
CVE References: CAN-2003-0352

W32.Blaster.T.Worm is a worm that exploits the DCOM RPC vulnerability (described in Microsoft Security Bulletin MS03-026 ) using TCP port 135. The worm targets only Windows 2000 and Windows XP computers.

While Windows NT and Windows 2003 servers are vulnerable to the exploit if they are not properly patched, the worm is not coded to replicate to those systems.

W32.Blaster.T.Worm does not have a mass-mailing functionality.

For additional information, read the Microsoft article, "What You Should Know About the Blaster Worm and Its Variants ."

We recommend that you block access to TCP port 4444 at the firewall level. Also block the following ports if you do not use either DCOM RPC or TFTP:

  • Block TCP Port 135 if you do not use DCOM RPC.
  • Block UDP Port 69 if you do not use TFTP.

The worm also attempts to perform a Denial of Service (DoS) on the Microsoft Windows Update Web server (windowsupdate.com). This is an attempt to prevent you from applying a patch on your computer against the DCOM RPC vulnerability.

Click here for more information on the vulnerability that this worm exploits and to find out which Symantec products can help mitigate the risks of this vulnerability. This information was added as a specific detection beginning with the virus definitions dated April 21, 2004. Virus definitions prior to this date (beginning with definitions released February 23, 2004 (20040223.007), detect this threat as Bloodhound.Packed or W32.Blaster.Worm.

Antivirus Protection Dates

  • Initial Rapid Release version April 21, 2004
  • Latest Rapid Release version August 20, 2008 revision 017
  • Initial Daily Certified version April 21, 2004
  • Latest Daily Certified version August 20, 2008 revision 016
  • Initial Weekly Certified release date April 21, 2004

Click here for a more detailed description of Rapid Release and Daily Certified virus definitions.

Technical Description

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

  1. Checks to see whether a computer is already infected and the worm is running. If so, the worm will not infect the computer a second time.

  2. Copies itself as the following files:
    • %System%\eschlp.exe
    • %System%\svchosthlp.exe

      Note: %System% is a variable. The worm locates the System folder and copies itself to that location. By default, this is C:\Windows\System (Windows 95/98/Me), C:\Winnt\System32 (Windows NT/2000), or C:\Windows\System32 (Windows XP).

  3. Adds the values:
    • "Helper" = "%System%\eschlp.exe /fstart"
    • "MSUpdate" = "%System%\svchosthlp.exe"

      to the registry key:


      so that the worm runs when you start Windows.

  4. Creates the key:


  5. Generates an IP address and attempts to infect the computer that has that address.

  6. Sends data on TCP port 135 that may exploit the DCOM RPC vulnerability. The worm sends one of two types of data: either to exploit Windows XP or Windows 2000.

    • The local subnet will become saturated with port 135 requests.
    • While W32.Blaster.T.Worm cannot spread to the Windows NT or Windows Server 2003, unpatched computers running these operating systems may crash as a result of the worm's attempts to exploit them. However, if the worm is manually placed and executed on a computer running these operating systems, it can run and spread.
    • Due to the random nature of how the worm constructs the exploit data, this may cause the RPC service to crash if it receives incorrect data. This may manifest as svchost.exe, generating errors as a result of the incorrect data.
    • If the RPC service crashes, the default procedure for Windows XP and Windows Server 2003 is to restart the computer. To disable this feature, see step 1 of the "Removal Instructions" below.

  7. Uses Cmd.exe to create a hidden remote shell process that will listen on a random TCP port, allowing an attacker to issue remote commands on an infected computer.

  8. Listens on UDP port 69. When the worm receives a request from a computer to which it was able to connect using the DCOM RPC exploit, it sends mschost.exe to that computer, and then executes it.

  9. Changes the Internet Explorer start page to http:/ /www.getgood.biz.


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.


Important Notes:
  • W32.Blaster.T.Worm exploits the DCOM RPC vulnerability. This is described in Microsoft Security Bulletin MS03-026, and a patch is available there. You must download and install the patch. In many cases, you will need to do this before continuing with the removal instructions. If you are not able to remove the infection or prevent re-infection using the following instructions, first download and install the patch.
  • Because of the way the worm works, it may be difficult to connect to the Internet to obtain the patch, definitions, or a removal tool before the worm shuts down the computer. There are at least two known ways to work around this, although both solutions do not work 100% completely all the time.
    • If you run Windows XP, activating the Windows XP firewall may allow you to download and install the patch, obtain virus definitions, and run the removal tool. This may also work with other firewalls, although this has not been confirmed.
    • In many cases, on both Windows 2000 and XP, changing the settings of the Remote Call Procedure (RPC) service may allow you to connect to the Internet without shutting down the computer.

      Follow these steps:
      1. Do one of the following:
        • Windows 2000: Right-click the My Computer icon on the Windows desktop, and then click Manage. The Computer Management window opens.
        • Windows XP: Click the Start button, right-click the My Computer icon, click Manage. The Computer Management window opens.

      2. In the left pane, double-click Services and Applications, and then select Services. A list of services appears.
      3. In the right pane, locate the Remote Procedure Call (RPC) service.

        CAUTION: There is also a service named Remote Procedure Call (RPC) Locator. Do not confuse the two.

      4. Right-click the Remote Procedure Call (RPC) service, and then click Properties.
      5. Click the Recovery tab.
      6. Using the drop-down lists, change First failure, Second failure, and Subsequent failures to "Restart the Service."
      7. Click Apply, and then click OK.

        CAUTION: Make sure that you change these settings back when you have removed the worm.

    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 XP).
    2. Update the virus definitions.
    3. Restart the computer in Safe mode or VGA mode.
    4. Run a full system scan and delete all the files detected as W32.Blaster.T.Worm.
    5. Reverse the changes that the Trojan made to the registry.
    For specific details on each of these steps, read the following instructions.

    1. To disable System Restore (Windows 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:
    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. To update 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. To restart the computer in Safe mode or VGA mode
    Shut down the computer and turn off the power. Wait for at least 30 seconds, and then restart the computer in Safe mode or VGA mode.
    • For Windows 95, 98, Me, 2000, or XP users, restart the computer in Safe mode. For instructions, read the document, "How to start the computer in Safe Mode."
    • For Windows NT 4 users, restart the computer in VGA mode.
    4. To scan for and delete the infected files
    1. Start your Symantec antivirus program and make sure that it is configured to scan all the files.
    2. Run a full system scan.
    3. If any files are detected as infected with W32.Blaster.T.Worm, click Delete.

    5. To reverse the changes made to the registry

    CAUTION : 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.
    1. Click Start, and then click Run. (The Run dialog box appears.)
    2. Type regedit

      Then click OK. (The Registry Editor opens.)

    3. Navigate to the key:


    4. In the right pane, delete the value:
      • "Helper" = "%System%\eschlp.exe /fstart"
      • "MSUpdate" = "%System%\svchosthlp.exe"

    5. Delete the key:


    6. Exit the Registry Editor.

    Writeup By: Benjamin Nahorney