How can I stealth port 113?

[BritishNemesis]

Just was running some tests over at https://grc.com/ and found that although my port 113 was closed it was not stealthed. They had a neat little writeup on it https://grc.com/port_113.htm and I was just wondering how one would go about stealthing this port as my router just doesn't seem to block out the port no matter what I try. I've got a built in firewall in redhat that I use but nothing specified in ipchains or whatever. I also run my own webserver so it said that that port was open (which of course it was) and I was wondering if there are any security vulnerabilities with that as well?

Can anyone give me a really good way of nailing down these ports so I can host a web server securely?

[Hubbe]

You have to remember that from the moment you connect to the internet you are never 100% protected. You run your own webserver (probably apache) on an open port, ofcourse there are security vulnerabilities. All it needs for example is a bug in the code and someone to exploit it.

Now you give very litle information about your hardware. So it is a litte difficult to give you help. You have port 113 closed, that means that no connection can be establiched trough that port. It is totaly safe. The problem is that your computer responds to a query to port 113 so even if all your other ports is stelthed a possible hacker knows that you exists, so ofcourse the best idea would to get it in stealth mode.

Now you don't say what kind of software firwewall you are using or witch distro you are using, so it is a little difficult to give you some help.
But if you have a newer distro that have the iptables module in the kernel you could write it a little like this to stealth port 113.

$IPTABLES -A INPUT -i eth0 -m state --state NEW,ESTABLISHED,RELATED -p tcp -s $UNIVERSE -d $EXTIP --dport 113 -j drop

[Vaseline]

113 is visible intentionally because it's requested all the time, and will slow things down if stealthed when you're trying to connect to most IRC networks for example..