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From "Sergey Tsalkov" <>
Subject [users@httpd] need help fighting DoS attack on Apache
Date Sun, 28 May 2006 17:50:29 GMT
Hey guys.. My Apache was hit with a DoS attack, where the attacker was
opening connections to the server and not sending any data. It quickly
reached the MaxClients limit and prevented any further connections to
the server.

The Server Status was filled with lines like this:
7-2	4039	0/8/8	R 	0.01	3	25	0.0	0.01	0.01 	?	?	..reading..

..and the apache log with lines like this: - - [28/May/2006:17:26:24 +0000] "-" 408 - "-" "-"

For some reason, Apache isn't listing the IP of the connection in
Server Status until that connection actually makes a request. Anyone
know why?

Anyways, I tried mod_choke's functionality for limiting multiple
connections from the same IP. That didn't help.. I suspect mod_choke
doesn't activate until a request is received through the connection,
so this script can dodge it by opening connections, not requesting
anything, and keeping them open until they time out. mod_evasive was
similarly unhelpful.

I managed to stop the attack by setting IP bans at the firewall, but
that doesn't actually solve the core problem.

Anyone have any suggestions?

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