Using NBAR to block Nimda


Does anyone have a comprehensive filter to stop Nimda using Cisco's NBAR?


__________________________ _______________________

Matthew E. Martini, PE, Inc. (631) 543-1000 x104
Chief Technology Officer (631) 864-8896 Fax


Look at the following two URLs and then combine the config:

Alex Yeung

cco login required, thanks anyway

replace "customer" with "public"


Replacing the word "customer" with "public" usually fixes that...

] >
] >
] cco login required, thanks anyway

Try the non-CCO versions here:

I've been collecting the blocking info from today and yesterday's
nanog onto a page:

So far:
     ipfw ruby script
     procmail rulesets
     F5 Big IP
     Nortel/Alteon topology trap
     Cisco NBAR
     Cisco CSS11K, Cisco Content Engine
     apache (updated w/mod_throttle info)
     iptable deny


Matt Martini wrote:

The basics of using NBAR as an IDS can be found here:

The page above is specifically for Code Red, but the same technique can be
used for blocking many different exploits. Just modify the class map as you
like to block Nimda or anything else.


I'm presently running using the policy map config example, and having some real problems. While the traffic is no longer getting to the servers, the servers wind up with massive quantities of open TCP sessions. These take long enough to die that Apache winds up maxing out on processes. Two possible alternative approaches that I'd like to explore:

1. Some mechanism that builds on the present stuff, but sends a TCP RST off to the web server to get the TCP session terminated.

2. Alternative approach: use the timed access lists to place a temporary filter rule into the input filter for any IP address which matches on URL. This would protect the servers better, in that it'd block the TCP connections (after the first one) from a server entirely. This wasn't an issue really for CodeRed, but is a major issue for nimda, since it opens many connections.

If anyone has insight on how to implement either of these, I'd like to hear about it.