Discovered: August 13, 2003
Updated: February 13, 2007 12:05:22 PM
Also Known As: W32/Blaster-B [Sophos], W32/Lovsan.worm.b [McAfee], Win32.Poza.B [CA], WORM_MSBLAST.C [Trend], Worm.Win32.Lovesan.a [Kaspersk
Type: Worm
Systems Affected: Windows



W32.Blaster.C.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 machines. While Windows NT and Windows 2003 Server machines are vulnerable to the aforementioned exploit if it is not properly patched, the worm is not coded to replicate to those systems.

This worm attempts to download the Teekids.exe file to the %WinDir%\System32 folder, and then execute it. This worm does not have any mass-mailing functionality.

W32.Blaster.C.Worm may have been distributed in a package that also contained a Backdoor Trojan.

The package would have had the following characteristics:

  • index.exe (32,045 bytes): Drops the worm and Backdoor components. It is detected as W32.Blaster.C.Worm.
  • root32.exe (19,798 bytes): Backdoor component detected as Backdoor.Lithium.
  • teekids.exe (5,360 bytes): Worm component detected as W32.Blaster.C.Worm.

We recommend that you block access to TCP port 4444 at the firewall level, and then block the following ports, if they do not use the following applications:
  • TCP Port 135, "DCOM RPC"
  • UDP Port 69, "TFTP"

The worm also attempts to perform a Denial of Service (DoS) on the Microsoft Windows Update Web server (www.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 risks from this vulnerability.

Antivirus Protection Dates

  • Initial Rapid Release version August 13, 2003
  • Latest Rapid Release version August 08, 2016 revision 023
  • Initial Daily Certified version August 13, 2003
  • Latest Daily Certified version August 09, 2016 revision 001
  • Initial Weekly Certified release date August 13, 2003

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


Technical Description


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

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

  2. Adds the value:

    "Microsoft Inet Xp.."="teekids.exe"

    to the registry key:

    HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Run

    so that the worm runs when you start Windows.

  3. Generates an IP address and attempts to infect the computer that has that address. The IP address is generated according to the following algorithms:
    • For 40% of the time, the generated IP address is of the form A.B.C.0, where A and B are equal to the first two parts of the infected computer's IP address.

      C is also calculated by the third part of the infected system's IP address; however, for 40% of the time the worm checks whether C is greater than 20. If so, a random value less than 20 is subtracted from C. Once the IP address is calculated, the worm will attempt to find and exploit a computer with the IP address A.B.C.0.

      The worm will then increment the 0 part of the IP address by 1, attempting to find and exploit other computers based on the new IP address, until it reaches 254.

    • With a probability of 60%, the generated IP address is completely random.

  4. 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. For 80% of the time, Windows XP data will be sent; and for 20% of the time, the Windows 2000 data will be sent.

    NOTES:
    • The local subnet will become saturated with port 135 requests.
    • While W32.Blaster.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 under Windows XP and Windows Server 2003 is to restart the computer. To disable this feature, see step one of the Removal Instructions below.

  5. Uses Cmd.exe to create a hidden remote shell process that will listen on TCP port 4444, allowing an attacker to issue remote commands on an infected system.

  6. 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 will send teekids.exe to that computer and tell it to execute the worm.

  7. If the current date is the 16th through the end of the month for the months of January to August, or if the current month is September through December, the worm will attempt to perform a DoS on Windows Update. However, the attempt to perform the DoS will succeed only if one the following conditions is true:
    • The worm runs on a Windows XP computer that was either infected or restarted during the payload period.
    • The worm runs on a Windows 2000 computer that was infected during the payload period and has not been restarted since it was infected.
    • The worm runs on a Windows 2000 computer that has been restarted since it was infected, during the payload period, and the currently logged in user is Administrator.

  8. The DoS traffic has the following characteristics:
    • Is a SYN flood on port 80 of windowsupdate.com.
    • Tries to send 50 HTTP packets every second.
    • Each packet is 40 bytes in length.
    • If it cannot find a DNS entry for windowsupdate.com, the worm uses a destination address of 255.255.255.255.
    Some fixed characteristics of the TCP and IP headers are:
      • IP identification = 256
      • Time to Live = 128
      • Source IP address = a.b.x.y, where a.b are from the host ip and x.y are random. In some cases, a.b are random.
      • Destination IP address = dns resolution of "windowsupdate.com"
      • TCP Source port is between 1000 and 1999
      • TCP Destination port = 80
      • TCP Sequence number always has the two low bytes set to 0; the 2 high bytes are random.
      • TCP Window size = 16384


Symantec ManHunt
  • Symantec ManHunt Protocol Anomaly Detection technology detects the activity associated with this exploit as "Portsweep." Although ManHunt can detect the activity associated with this exploit with the Protocol Anomaly Detection technology, you can use the "Microsoft DCOM RPC Buffer Overflow" custom signature, released in Security Update 5, to precisely identify the exploit being sent.
  • Symantec ManHunt Protocol Anomaly Detection technology detects the activity associated with the Denial of Service SYN flood. Security Response has created a custom signature for ManHunt 3.0, released in Security Update 6, to detect this attack specifically as a Blaster DDoS Request.

Enterprise Security Manager
Symantec Security Response posted a Response Policy for this vulnerability on July 17, 2003.

Symantec Enterprise Firewall
Symantec's full application inspection firewall technology protects against the W32.Blaster.C.Worm, blocking all the above listed TCP ports by default.

Norton Internet Security, Norton Personal Firewall
By default, these Symantec products have the EPMAP rule to block TCP port 135.

Recommendations

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.


Removal


Removal using the W32.Blaster.C.Worm Removal Tool
Symantec Security Response has developed a removal tool to clean the infections of W32.Blaster.C.Worm. Try this tool first, as it is the easiest way to remove this threat.


Manual Removal
As an alternative to using the removal tool, you can manually remove this threat. The following instructions pertain to all current and recent Symantec antivirus products, including the Symantec AntiVirus and Norton AntiVirus product lines.

  1. Restore Internet connectivity.
  2. End the worm process.
  3. Obtain the latest virus definitions.
  4. Scan for and delete the infected files.
  5. Reverse the changes made to the registry.
  6. Obtain the Microsoft HotFix to correct the DCOM RPC vulnerability


For specific details, refer to the following instructions:

1. Restoring Internet connectivity
In many cases, on both Windows 2000 and XP, changing the settings for the Remote Procedure Call (RPC) service may allow you to connect to the Internet without the computer shutting down. To restore Internet connectivity to your PC, follow these steps:
    1. Click Start > Run. The Run dialog box appears.
    2. Type:

      SERVICES.MSC /S

      in the open line, and then click OK. The Services window opens.

    3. In the left pane, double-click Services and Applications, and then select Services. A list of services appears.
    4. 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.

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


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

2. Ending the Worm process
  1. Press Ctrl+Alt+Delete once.
  2. Click Task Manager.
  3. Click the Processes tab.
  4. Double-click the Image Name column header to alphabetically sort the processes.
  5. Scroll through the list and look for teekids.exe.
  6. If you find the file, click it, and then click End Process.
  7. Exit the Task Manager.
    3. Obtaining the latest 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:
      For newer computer users
      Running LiveUpdate, which is the easiest way to obtain virus definitions: Virus definitions for W32.Blaster.worm have been made available via the LiveUpdate server since August 11th, 2003. To obtain the latest virus definitions, click the LiveUpdate button from within the main user interface of your Symantec product. When running LiveUpdate, ensure that only "Norton AntiVirus Virus Definitions" are checked. Product updates can be obtained at a later time.

      For system administrators and advanced users
      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.
    4. 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.
    2. Run a full system scan.
    3. If any files are detected as infected with W32.Blaster.Worm, click Delete.

    5. Reversing the changes made to the registry


    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.
    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:

      HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Run

    4. In the right pane, delete the value:

      "Microsoft Inet Xp.."="teekids.exe"

    5. Exit the Registry Editor.

    6. Obtaining the Microsoft HotFix to correct the DCOM RPC vulnerability
    W32.Blaster.Worm is a worm that exploits the DCOM RPC vulnerability using TCP port 135 to infect your PC. The W32.Blaster.Worm also attempts to perform a DoS on the Microsoft Windows Update Web server (windowsupdate.com) using your PC. To fix this, it is important to obtain the Microsoft Hotfix at: Microsoft Security Bulletin MS03-026 .



    Writeup By: Douglas Knowles