[CentOS] Paranoid Firewalling
t004 at kbocek.com
Wed Sep 7 01:02:08 UTC 2005
I'm familiar with 'port-knocking' and after mulling it over decided to
simply use the 'PermitRootLogin without-password' option to sshd. I
looked at the user names being testing in the scripts and decided that
it was unlikely anyone would hit one of our users, especially with the
security script I had installed. Forcing DSA keys for root access solved
my last concern.
Maciej Żenczykowski wrote:
> Instead of keeping the ssh port open, use something like the following:
> -A INPUT -p tcp --dport SECRETPORT# -m recent --set
> -A INPUT -p tcp --dport ssh -m state --state NEW -m recent --update
> --seconds 43200 -j ACCEPT
> and then before ssh'ing in from outside telnet the SECRETPORT# on the
> machine in order to open the ssh port for the next 12 hours.
> Gets rid of script kiddies.
> On Tue, 6 Sep 2005, Sam Drinkard wrote:
>> If you don't mind, could you let me know where that script is? I'm
>> seeing the same thing -- kiddies trying to log in. I use something
>> similar, but manual entry on my mail server that is in a co-lo site
>> running FreeBSD. Here at home, I thought I'd be pretty well protected
>> behind the router, but I have to have the ssh port open, and I'm
>> seeing hundreds of attempts. Thanks...
>> Kirk Bocek wrote:
>>> Good question Alex. However, I've never studied the scripts that
>>> 'script kiddies' use and so have no answer.
>>> Part of what has prompted this change is the recent surge of
>>> brute-force password attacks. From the timing of the password
>>> attempts, it's clear that these are script driven.
>>> I found a perl script that watches for failed logins. After a
>>> configurable number, the script enters the IP address into
>>> /etc/hosts.deny. After a configurable number of days, the script then
>>> removes the IP address.
>>> What I see in /var/log/secure is a whole series of 'Invalid user'
>>> messages followed by 'Failed password for invalid user' messages.
>>> These will then, because of the script, be terminated by a 'refused
>>> connect from' message when the address is entered into hosts.deny.
>>> My point in all this is that I only ever see *one* 'refused connect'
>>> message. So at least for this script, it gives up when it can't
>>> connect anymore.
>>> Kirk Bocek
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