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Re: Dynamic DNS "Spoofing" & IRC
From: c4 <c4 () jolt nu>
Date: Fri, 02 May 2003 17:53:45 +0200

Well you dont even have to have dyndns... just control over the over the domain is sufficient.
Just connect and change the dns afterwards...

This dosn't have anything to do with dns & irc really... it just utilizes the fact that your ircclient performs a dns check seperatly.

The problem with rechecking dns is that for a pretty large network such as ircnet or efnet it would take some resources to do this check, thus allowing a denial attack being made more easily against one server.

At 23:47 2003-05-01, you wrote:
This is a trivial "feature/flaw" I've been holding onto for a bit, and it's
probably commonly known, but I haven't seen it posted anywhere, more of a
neat little thing in taking advantage of IRC and it's treatment of dyndns
within DNS if reverse lookup is possible.

IRC (Internet Relay Chat) servers being a common ground for chat, have some
annoyances such as the username () ipaddress or username () domainname, some
people don't like that etc, being that they have to use a bouncer to avoid
showing their own ip address or hostname to other users if they want to
maintain some sort of privacy.

Well here's a pseudo-privacy trick that can be reasonably easy to perform
given one has control of a dns server that performs reverse and forward
lookups, support for dyndns scripts, and a domain-name registered to you.
You can optionally use a bouncer if you want.

In my example, I will use the host name spooftest.domain.com, a port
forwarding tool, a zoneedit account with my dyndns script that forward
resolves, and a friend's server (he/she runs an isp) that allows for me to
have an PTR record to the ip address "" (<-- this is a private
address for demo purposes) on his server as spooftest.domain.com

Step 1) I have zoneedit script set up to tell it that my dyndns address is
to spooftest.domain.com is, which it updates immediately and the server has PTR record for as spooftest.domain.com (thus
allowing reverse and forward lookup of spooftest.domain.com)
My portforward (say we're using datapipe.c on the box)
settings are datapipe 6667 irc.whateverserver.net 6667

Step 2) Log into irc server on your local machine by doing a /server
spooftest.domain.com 6667, make sure the irc server has resolved you as
username () spooftest domain com

Step 3) Run your dyndns script for zoneedit to assign your ip address as
whatever ip you want (in this case I'll use, then wait about a
minute before joining a channel.

By this time, your dyndns should have updated and changed your ip address to, and irc servers don't re-check after you've connected (so anyone
resolving your hostname will come up with

I don't know if this is categorized as a flaw in dns or irc, or just merely
exploiting a feature, and this is a rather trivial trick (surely can't be
original and I apologize if it's been posted before).

A fix I think would have ircd recheck after a certain amount of time for
resolving properties of their dns, and I was going to say dnssec, but I
can't really see that fixing the problem unless ircd re-checks as well

This "feature/flaw" could probably apply to other application protocols as
well that do not recheck dns properties, but I haven't taken the time to
come up for other practical uses for it.

This has been tested on most ircd server versions and all so far are victim
to this "hack".


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