1. Symantec/
  2. Security Response/
  3. W32.Blaster.K.Worm


Risk Level 2: Low

February 3, 2004
February 13, 2007 12:17:01 PM
Also Known As:
W32.Blaster.Worm, WORM_MSBLAST.H [Trend], Worm.Win32.Lovesan.a [Kaspersk, W32/Lovsan.worm.gen [McAfee]
Systems Affected:

W32.Blaster.K.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. This worm attempts to download the mschost.exe file into the %Windir%\System32 folder, and then execute it.

W32.Blaster.K.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, and then block the following ports, if you 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 (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.

Note: Virus Definitions released August 13, 2003 (20030813.009) detect this threat as W32.Blaster.Worm

Antivirus Protection Dates

  • Initial Rapid Release version February 4, 2004
  • Latest Rapid Release version August 20, 2008 revision 017
  • Initial Daily Certified version February 4, 2004
  • Latest Daily Certified version August 20, 2008 revision 016
  • Initial Weekly Certified release date February 4, 2004
Click here for a more detailed description of Rapid Release and Daily Certified virus definitions.
Writeup By: Kevin Ha

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