Sounds like you were hit by Slowloris (http://ha.ckers.org/slowloris/ ).
AFAIK there is no way to defend against it with Apache, other than using
some external service or a reverse proxy that is not vulnerable to it.
Perhaps this might help: http://www.funtoo.org/en/security/slowloris/

Also, it was not necessarily distributed since the nature of attack
could allow single machine used to attack. What do your logs say, how
many IPs were involved?


Vlad

On 04/26/10 05:36, cd34 wrote:
> After dealing with a DDOS today on a site (non-pylons, but the issue
> is still the same), it became very evident that there are very few
> hooks in apache that allow you to drop a connection where it needs to
> be dropped.  mod_security/mod_evasive don't hook apache early enough
> in the request phase to actually do what is needed.
>
> While fail2ban will work, IF you can identify the traffic, it does
> require the request to hit the logs.  The problem with this attack was
> that the requests never hit the logs, but, apache was dispatching to
> the child waiting for the request to complete.  I guess I could have
> run mod_forensic to see what the connections were, but, it wasn't
> compiled for this machine's architecture.
>
> iptables --recent support would have worked, but, the server was much
> too busy for that to work.  In the end, I had to move over to nginx
> and use their limit_conn rule to prevent the attacks from overloading
> the machine.  While I generally loathe throttling to control a DDOS,
> it did seem to handle it.  Any load balancer may have prevented the
> traffic from hitting the origin server.  Using varnish probably would
> have worked, but, would have required backend changes due to the IP
> address always showing the varnish server's IP.  mod_rpaf would allow
> that to be remedied, but, Varnish changes things in mysterious ways at
> times.
>
>   

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