1. Symantec/
  2. Security Response/
  3. W32.Welchia.Worm


Risk Level 2: Low

August 18, 2003
February 13, 2007 12:05:08 PM
Also Known As:
W32/Welchia.worm10240 [AhnLab], W32/Nachi.worm [McAfee], WORM_MSBLAST.D [Trend], Lovsan.D [F-Secure], W32/Nachi-A [Sophos], Win32.Nachi.A [CA], Worm.Win32.Welchia [Kaspersky]
Systems Affected:
Microsoft IIS, Windows
CVE References:
CAN-2003-0109 CAN-2003-0352

As of February 26, 2004, due to a decreased rate of submissions, Symantec Security Response has downgraded this threat to a Category 2 from a Category 3.

W32.Welchia.Worm is a worm that exploits multiple vulnerabilities, including:
  • The DCOM RPC vulnerability (first described in Microsoft Security Bulletin MS03-026) using TCP port 135. The worm specifically targets Windows XP machines using this exploit. Users are recommended to patch this vulnerability by applying Microsoft Security Bulletin MS03-039.
  • The WebDav vulnerability (described in Microsoft Security Bulletin MS03-007) using TCP port 80. The worm specifically targets machines running Microsoft IIS 5.0 using this exploit. As coded in this worm, this exploit will impact Windows 2000 systems and may impact Windows NT/XP systems.

W32.Welchia.Worm does the following:
  • Attempts to download the DCOM RPC patch from Microsoft's Windows Update Web site, install it, and then restart the computer
  • Checks for active machines to infect by sending an ICMP echo request, or PING, which will result in increased ICMP traffic
  • Attempts to remove W32.Blaster.Worm

Security Response has provided some information to aid network administrators in ongoing efforts to track down the machines that W32.Welchia.Worm has infected on their respective network. Read the document, "Detecting traffic due to RPC worms," for additional information.

Antivirus Protection Dates

  • Initial Rapid Release version August 18, 2003
  • Latest Rapid Release version March 23, 2017 revision 037
  • Initial Daily Certified version August 18, 2003
  • Latest Daily Certified version March 23, 2017 revision 041
  • Initial Weekly Certified release date August 18, 2003
Click here for a more detailed description of Rapid Release and Daily Certified virus definitions.
Writeup By: Frederic Perriot

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