Symantec:W32.Welchia.Worm LEVEL 4

The world leader in Internet security, today announced that it has upgraded the W32.Welchia.Worm from a level two to a level four threat. Once inside corporate perimeters, W32.Welchia.Worm propagates at a rabid pace.

Symantec is receiving reports of severe disruptions on the internal networks of large enterprises caused by ICMP flooding related to the propagation of the W32.Welchia.worm. In some cases enterprise users have been unable to access critical network resources.

Despite its original intent, the W32.Welchia.Worm is an insidious worm that is preventing IT administrators from cleaning up after the W32.Blaster.Worm, said Patrick Evans, regional manager for Africa at Symantec. The worm is swamping network systems with traffic and causing denial-of-service to critical servers within organisations.

W32.Welchia.Worm targets computers infected with the W32.Blaster.Worm. Once on a system, W32.Welchia.Worm deletes msblast.exe, attempts to download the DCOM RPC patch from Microsoft's Windows Update Web site, installs the patch, and then reboots the computer. The worm checks for active machines to infect by sending an ICMP echo, or PING, which may result in significantly increased ICMP traffic. ICMP is a TCP/IP protocol used to send Internet messages.

Although corporations may have perimeter defences in place, in response to the W32.Blaster.Worm, internal infections are still running high, said Evans. Deployment of the security patch in large, geographically dispersed environments is expected to take weeks to months to complete. Both the W32.Blaster.Worm and W32.Welchia.Worm are clear examples of why comprehensive security measures need to be deployed at various tiers of the network including policy compliance for remote access users.

W32.Welchia.Worm propagates through TCP port 135 on Windows XP and Windows 2000 machines that have not patched the Microsoft Windows DCOM RPC Interface Buffer Overrun Vulnerability. Additionally, the worm propagates through TCP port 80 on Microsoft IIS 5.0 systems that have not patched the Microsoft Windows WebDav (ntdll.dll) Buffer Overflow Vulnerability.

Symantec DeepSight Threat Management System is currently reporting anomalous levels in the number of source IPs targeting both TCP Port 80 and the Microsoft Windows Web Dav Buffer Overflow Vulnerability. TCP Port 135 continues to be a prominently targeted port due to the activities of both W32.Blaster.Worm and W32.Welchia.Worm.

Administrators are strongly urged to ensure that patches have been applied to systems vulnerable to either the Microsoft Windows DCOM RPC Interface Buffer Overrun Vulnerability or Microsoft Windows WebDav Buffer Overflow Vulnerability.

W32.Welchia.Worm Removal Tool Symantec Security Response has posted a removal tool for W32.Welchia.Worm. The removal tool is available here.