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Dealing with ftp attacks

Just a thought,

if you can detect an attack, script a block of that IP only, and  
unlock it after an hour or two, again with a script.

if you have known customers (internal users?) you could make an  
authorized table and block everyone else from China.

Just a thought.  I don't know the FTP daemon, but the concept seems good.

Quoting John Abreau <john.abreau at>:

> What's the recommended way of dealing with ftp attacks?
> We have an ftp server for supporting our customers, running vsftpd,
> and every once in a while it's come under attack from somewhere
> in China; the attacker slams the ftp port, showing an authentication
> failure every 3 seconds, continuously until the server locks up
> four hours later.
> It happened yesterday evening, and I had to waste a few hours
> driving into work to power-cycle the server. I set up a script
> to scan the logs hourly and page me if it detected an attack,
> and about an hour after I got home, at 2 am, I got a report of
> a second attack.
> I dealt with it by blocking the ip addresses with
>     route add -net reject
> which interrupted the attack before the server could lock up.
> And I just got yet another alert, a few minutes ago; these
> assholes seem determined to break in.
> One concern I have is that these routes will gradually
> clog up my routing table. Also, this machine is our external
> mail server, and we have customers in China, so I can't just
> block off all of China.
> --
> John Abreau
> IT Manager
> Zuken USA
> 238 Littleton Rd., Suite 100
> Westford, MA 01886
> T: 978-392-1777            F: 978-692-4725
> M: 978-764-8934
> E: John.Abreau at  W:

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