nion's blog

There are many servers using tools like fail2ban, denyhosts or blockhosts to defend their machine from different brute force attacks especially on ssh.

It is old news that this can lead to dangerous results because of stuff like IP spoofing.

The following paper on http://www.ossec.net/en/attacking-loganalysis.html which came across full-disclosure today shows how to do DoS attacks on a server running these tools using a technique very similar to SQL injections, called log injection.

This shows another time that it might be very self-desctructive if you use such tools.
So if you use one of the services, patch them, this attack can be run by everyone capable of open a shell and use netcat/telnet/foo.