Untitled

malllllllll
The code presented here is a subset of
my alpha perl spoofer, slapfro, which is
available from 9mm.com/philez.html. I
thought it would be nice to see something
other than a knockoff of a knockoff of a
spoofer for once and maybe give some
more people the ability to play with the insides
of tcplip.
Greetz, boys and gurliez. Today, we play
with the insides of tcplip. In particular,
we'll be building a tcp spoofer in perl
(yeah, you can do icmp or udp too if ya
want). We'll call this one - umm - lego. All
we really want to do with lego is build our
own packets. This can be useful if you like
to set the source address to something arbitrary,
or if you want to experiment with
flags or some shit. We're not going to do tcp
connection spoofing, because that would be
too big in scope for our purposes. At this
point we'll just send out some tcp packets
with increasing port numbers, sort of like
the way a half-opened portscan would look.
If lots of people begin to use this, we get
the added benefit of making uptight sysadmins
look silly, and finally teaching them
that portscaning is neither harmful, intrusive,
nor necessarily evidenee that anything
at all came from the apparent source of the
scan. Ahem.
DD mill
There are three main sections of code
that we will use to create our packet: the
first sets up things like source and destination
address, ports, number of packets, and
any looping and shit that we might use to
send lots of packets or to vary the packets,
say, by incrementing the destination port
each time we send. The second section is
the guts: we figure out what our ip and tcp
headers will look like, then we put the
packet together. The third section calculates
a checksum for the packet - used to tell the
receiving machine that the packet didn't get
mangled in transit. I admit, I ripped off the
checksum code from Net::Ping. Shit, who
wants to write checksum code when it's already
there for you? The three sections are
nested 1,2,3 - they each use the next as a
subroutine.
A Quick Tour
The first point of interest is the specifications
of target box, source box, and ports.
If your ambition is low and all you want to
do is watch some home-brewed tcp packets
fly, just put in some valid source and destination
addresses, run a sniffer, and enjoy.
For the slightly more motivated, you could
take these five items as parameters from the
command line.
Page 6 2600 Magazine Fall 1998