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How to block W32.Blaster in an enterprise MAN/WAN at Cisco Routers

Posted on 2004-05-01
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Last Modified: 2010-04-17
I have a customer with 9 locations connected together via T1 circuts.  The routers at the sites are Cisco 1721's with T1 WICs.   There are 60 Win2K servers with an Active Directory DC at each site.  Cisco's recommendation only addresses the router at the edge and will not work for the other routers in this scenerio.   Is there any way to block Blaster at the router level, using the 1721's that are currently in place, without stopping valid communications between sites and servers?
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Question by:JCRussell
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8 Comments
 
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Assisted Solution

by:lrmoore
lrmoore earned 125 total points
ID: 10972128
Simply block icmp echo on the local lan interface:

access-list 102 deny icmp any any echo
access-list 102 permit ip any any

Interface FastEthernet 0
 access-group 102 in


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Author Comment

by:JCRussell
ID: 10972262
From the activity that we are seeing, it appears that Blast is scanning ports.  All of the machines that have Blast are sending epmap packets with consecutive port numbers.  At least all the machines that are scanning have Blast.  Is this Blast or something else?  Will blocking icmp echos stop this activity?
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Expert Comment

by:lrmoore
ID: 10973493
blocking icmp echo requests will localize the outbreak to the local lan. The blast of icmp is what kills networks. At the very least, this will keep the infection localized and keep the extra traffic off of your WAN links until you can eradicate it.
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LVL 28

Expert Comment

by:mikebernhardt
ID: 10980281
Also block TCP port 135 (DCom), which is what Blaster propagates itself with once it finds a live host. Although it will try port 80 also...
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Author Comment

by:JCRussell
ID: 10983202
Won't blocking 135 stop file sharing, etc.?
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Accepted Solution

by:
mikebernhardt earned 125 total points
ID: 10988071
Nope. It's not used for anything useful. It amost seems as if it was designed to give hackers a good tool for worms.

http://grc.com/dcom/
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