Re: Automatic blocking

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]


On Wed, 16 Aug 2006 04:25:38 -0600, Ashley M. Kirchner wrote:

>     I looked around on the web and found a few different programs to do 
> this, so I thought I'd ask here for advice: what are people using to 
> automatically block incoming attacks via ssh and ftp?  I'm referring to 
> those script kiddies who simply hit your system over and over and over 
> again in a very short period of time, probing both the ssh as well as 
> the ftp daemons trying to log in.
>     And related to the question, what's the best practice here, adding 
> them to /etc/hosts.deny or dropping the traffic with iptables?

The answer to your question is portsentry. It runs in the background,
monitoring a list of ports for incoming connections. If an attacker
hits a port so many times in a short amount of time, portsentry
bans the offending machine, by introducing the appropriate rule
in iptables. Of course, the list of ports, and the threshold for
the number of hits are configurable. 

That said, cool as it may sound, portsentry has a major drawback
which made me and many others prefer a non-dynamic approach to
security. Portsentry can be used to produce a denial of service
attack. Suppose you connect regularly from your machine
to your machine, and knows that. Then can send packets to pretending to originate
from Then for all it knows, portsentry running on your will cut off acces to Sounds complicated, but
it's trivial to do that, with things like nc or nmap. 

There is also a good chance that you will lock yourself out
remotely, by accident, after a few failed login attempts from to your I did it, and had to drive home,
curse at the world, etc. Removed portsentry and used a sound
security policy instead.

If you are the only user to connect remotely via sshd, then
the easiest way to foil sshd brute force attacks is to run 
sshd on a non-default port (e.g. the birthday of your pet).
Specify that in /etc/ssh/sshd_config.

[Index of Archives]     [Current Fedora Users]     [Fedora Desktop]     [Fedora SELinux]     [Yosemite News]     [Yosemite Photos]     [KDE Users]     [Fedora Tools]     [Fedora Docs]

  Powered by Linux