[web-devel] questions about ResponseEnumerator

Greg Weber greg at gregweber.info
Mon Oct 24 15:59:11 CEST 2011

On Sun, Oct 23, 2011 at 7:50 PM, Kazu Yamamoto <kazu at iij.ad.jp> wrote:

> Hello,
> > Apache is considered vulnerable to slowloris because it has a limited
> thread
> > pool. Nginx is not considered vulnerable to slowloris because it uses an
> > evented architecture and by default drops connections after 60 seconds
> that
> > have not been completed. Technically we say our Haskell web servers are
> using
> > threads, but they are managed by a very fast evented system. So we can
> hold
> > many unused connections open like Nginx and should not be vulnerable if
> we
> > have a timeout that cannot be tickled. This could make for an interesting
> > benchmark - how many slowloris connections can we take on? The code from
> Kazu
> > makes just one connection - it does not demonstrate a successful
> slowloris
> > attack, just one successful slowloris connection.
> I you want, I create a code to do real slowloris attack to consume the
> file descriptors of a server. It's quite easy.

That depends on the file descriptor limits. If the server can take on more
connections that the attacking script can produce, you will need a second
machine, which I think means it is no longer quite easy. Slowloris was
designed to show how easy it is to take down servers with Apache style
architecture by just gradually opening 50 slow connections.

We are actually in the realm of DOS attacks now. Intentionally slowing down
the connection of the attack is just a technique to make the DOS more
effective, but I don't even know why it matters anymore to our situation -
the attacker can just send more requests to the server - I suppose the slow
connection is more effective at blocking out legitimate users competing for

> > If we limit the number of connections per ip address, that means a
> slowloris
> > attack will require the coordination of thousands of nodes and make it
> highly
> > impractical.
> If we pay money, we can use a *botnet* to do this. This actually
> happens in the real world. But I don't think a bad guy targets your
> web server.
> --Kazu
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