GUIDE TO (mostly) HARMLESS HACKING
Vol. 1 Number 2
In this issue we learn how to forge email -- and how
to spot forgeries. I
promise, this hack is spectacularly easy!
______________________________________________________________
Heroic
Hacking in Half an Hour
How would you like to totally blow away your friends? OK, what is the
hairiest thing you
hear that super hackers do?
It's gaining unauthorized access to a computer, right?
So how would you like to
be able to gain access and run a program on the
almost any of the millions of computers hooked up to the Internet? How
would
you like to access these Internet computers in the same way as the most
notorious hacker in history: Robert Morris!
It
was his "Morris Worm" which took down the Internet in 1990. Of course,
the flaw he exploited to fill up 10% of the computers
on the Internet with
his self-mailing virus has been fixed now -- on most Internet hosts.
But that same feature
of the Internet still has lots of fun and games and
bugs left in it. In fact, what we are about to learn is the first step
of
several of the most common ways that hackers break into private areas of
unsuspecting computers.
But I'm not
going to teach you to break into private parts of computers. It
sounds too sleazy. Besides, I am allergic to jail.
So
what you are about to learn is legal, harmless, yet still lots of fun. No
pulling the blinds and swearing blood oaths among
your buddies who will
witness you doing this hack.
But -- to do this hack, you need an on-line service which allows
you to
telnet to a specific port on an Internet host. Netcom, for example, will let
you get away with this.
But
Compuserve, America Online and many other Internet Service Providers
(ISPs) are such good nannies that they will shelter
you from this temptation.
But your best way to do this stuph is with a SHELL ACCOUNT! If you don't
have one yet,
get it now!
***********************************
Newbie note #1; A shell account is an Internet account that lets
you give
Unix commands. Unix is a lot like DOS. You get a prompt on your screen and
type out commands. Unix is the language
of the Internet. If you want to be
a serious hacker, you have to learn Unix.
****************************
Even
if you have never telnetted before, this hack is super simple. In fact,
even though what you are about to learn will look
like hacking of the most
heroic sort, you can master it in half an hour -- or less. And you only need
to memorize *two*
commands.
To find out whether your Internet service provider will let you do this
stuph, try this command:
telnet
callisto.unm.edu 25
This is a computer at the University of New Mexico. My Compuserve account
gets the vapors when
I try this. It simply crashes out of telnet without so
much as a "tsk, tsk."
But at least today Netcom will let
me do this command. And just about any
cheap "shell account" offered by a fly-by-night Internet service provider
will
let you do this. Many college accounts will let you get away with this,
too.
******************************
Newbie
note #2: How to Get Shell Accounts
Try your yellow pages phone book. Look under Internet. Call and ask for a
"shell
account."
They'll usually say, "Sure, can do." But lots of times they are lying. They
think you are too dumb to
know what a real shell account is. Or the
underpaid person you talk with doesn't have a clue.
The way around this
is to ask for a free temporary guest account. Any
worthwhile ISP will give you a test drive. Then try out today's hack.
*******************************
OK,
let's assume that you have an account that lets you telnet someplace
serious. So let's get back to this command:
telnet
callisto.unm.edu 25
If you have ever done telnet before, you probably just put in the name of
the computer you planned
to visit, but didn't add in any numbers afterward.
But those numbers afterward are what makes the first distinction between
the
good, boring Internet citizen and someone slaloming down the slippery slope
of hackerdom.
What that 25 means
is that you are commanding telnet to take you to a
specific port on your intended victim, er, computer.
***********************************
Newbie
note #3: Ports
A computer port is a place where information goes in or out of it. On your
home computer, examples of
ports are your monitor, which sends information
out, your keyboard and mouse, which send information in, and your modem,
which
sends information both out and in.
But an Internet host computer such as callisto.unm.edu has many more ports
than
a typical home computer. These ports are identified by numbers. Now
these are not all physical ports, like a keyboard or
RS232 serial port (for
your modem). They are virtual (software) ports.
***********************************
But
there is phun in that port 25. Incredible phun. You see, whenever you
telnet to a computer's port 25, you will get one
of two results: once in
awhile, a message saying "access denied" as you hit a firewall. But, more
often than not, you
get something like this:
Trying 129.24.96.10...
Connected to callisto.unm.edu.
Escape character is '^]'.
220
callisto.unm.edu Smail3.1.28.1 #41 ready at Fri, 12 Jul 96 12:17 MDT
Hey, get a look at this! It didn't ask us to
log in. It just says...ready!
Notice it is running Smail3.1.28.1, a program used to compose and send email.
Ohmigosh,
what do we do now? Well, if you really want to look sophisticated,
the next thing you do is ask callisto.unm.edu to tell
you what commands you
can use. In general, when you get on a strange computer, at least one of
three commands will get
you information: "help," "?", or "man." In this case
I type in:
help
... and this is what I get
250
The following SMTP commands are recognized:
250
250 HELO hostname startup and give
your hostname
250 MAIL FROM:<sender address> start transaction from sender
250
RCPT TO:<recipient address> name recipient for message
250 VRFY <address>
verify deliverability of address
250 EXPN <address>
expand mailing list address
250 DATA
start text of mail message
250 RSET
reset state, drop transaction
250 NOOP
do nothing
250 DEBUG [level]
set debugging level,default 1
250 HELP
produce this help message
250 QUIT
close SMTP connection
250
250 The normal sequence of events in sending a message is to state the
250 sender address
with a MAIL FROM command, give the recipients with
250 as many RCPT TO commands as are required (one address per command)
250
and then to specify the mail message text after the DATA command.
250 Multiple messages may be specified. End the
last one with a QUIT.
Getting this list of commands is pretty nifty. It makes you look really kewl
because you know
how to get the computer to tell you how to hack it. And it
means that all you have to memorize is the "telnet <hostname>
25 " and
"help" commands. For the rest, you can simply check up on the commands while
on-line. So even if your memory
is as bad as mine, you really can learn and
memorize this hack in only half an hour. Heck, maybe half a minute.
OK,
so what do we do with these commands? Yup, you figured it out, this is a
very, very primitive email program. And guess
why you can get on it without
logging in? Guess why it was the point of vulnerability that allowed Robert
Morris to
crash the Internet?
Port 25 moves email from one node to the next across the Internet. It
automatically takes incoming
email and if the email doesn't belong to
someone with an email address on that computer, it sends it on to the next
computer
on the net, eventually to wend its way to the person to who this
email belongs.
Oftentimes email will go directly
from sender to recipient, but if you email
to someone far away, or if the Internet is clogged with traffic, email may
go
through several computers.
There are millions of computers on the Internet that forward email. And you
can get
access to almost any one of these computers without a password!
Furthermore, as you will soon learn, it is easy to get
the Internet
addresses of these millions of computers.
Some of these computers have very good security, making
it hard to have
serious fun with them. But others have very little security. One of the joys
of hacking is exploring
these computers to find ones that suit ones fancy.
OK, so now that we are in Morris Worm country, what can we do with
it? Well,
here's what I did. (My commands have no number in front of them, whereas the
computer's responses are prefixed
by numbers.)
helo santa@north.pole.org
250 callisto.unm.edu Hello santa@north.pole.org
mail from:santa@north.pole.org
250
<santa@north.pole.org> ... Sender Okay
rcpt to:cmeinel@nmia.com
250 <cmeinel@nmia.com> ... Recipient Okay
data
354
Enter mail, end with "." on a line by itself
It works!!!
.
250 Mail accepted
What happened here is that
I sent some fake email to myself. Now let's take
a look at what I got in my mailbox, showing the complete header:
Here's
what I saw using the free version of Eudora:
X POP3 Rcpt: cmeinel@socrates
This line tells us that X-POP3 is
the program of my ISP that received my
email, and that my incoming email is handled by the computer Socrates.
*****************************
Evil
Genius Tip: incoming email is handled by port 110. Try telnetting there
someday. But usually POP, the program running on
110, won't give you help
with its commands and boots you off the minute you make a misstep.
*****************************
Return
Path: <santa@north.pole.org>
This line above is my fake email address.
Apparently From: santa@north.pole.org
Date:
Fri, 12 Jul 96 12:18 MDT
But note that the header lines above say "Apparently-From" This is important
because it
alerts me to the fact that this is fake mail.
Apparently To: cmeinel@nmia.com
X Status:
It works!!!
Now
here is an interesting fact. Different email reading programs show
different headers. So how good your fake email is depends
on part on what
email program is used to read it. Here's what Pine, an email program that
runs on Unix systems, shows
with this same email:
Return Path: <santa@north.pole.org>
Received:
from callisto.unm.edu by nmia.com
with smtp
(Linux Smail3.1.28.1
#4)
id m0uemp4 000LFGC; Fri, 12 Jul 96 12:20 MDT
This identifies the
computer on which I ran the smail program. It also tells
what version of the smail program was running.
Apparently
From: santa@north.pole.org
And here is the "apparently-from" message again. So both Pine and Eudora
show this is
fake mail.
Received: from santa@north.pole.org by callisto.unm.edu with smtp
(Smail3.1.28.1
#41) id m0uemnL 0000HFC; Fri, 12 Jul 96 12:18 MDT
Message Id: <m0uemnL 0000HFC@callisto.unm.edu>
Oh, oh!
Not only does it show that it may be fake mail -- it has a message
ID! This means that somewhere on Callisto there will
be a log of message IDs
telling who has used port 25 and the smail program. You see, every time
someone logs on to port
25 on that computer, their email address is left
behind on the log along with that message ID.
Date: Fri, 12 Jul
96 12:18 MDT
Apparently From: santa@north.pole.com
Apparently To: cmeinel@nmia.com
It works!!!
If
someone were to use this email program to do a dastardly deed, that
message ID is what will put the narcs on his or her
tail. So if you want to
fake email, it is harder to get away with it if you send it to someone using
Pine than if they
use the free version of Eudora. (You can tell what email
program a person uses by looking at the header of their email.)
But
-- the email programs on port 25 of many Internet hosts are not as well
defended as callisto.unm.edu. Some are better defended,
and some are not
defended at all. In fact, it is possible that some may not even keep a log
of users of port 25, making
them perfect for criminal email forgery.
So just because you get email with perfect-looking headers doesn't mean it
is
genuine. You need some sort of encrypted verification scheme to be almost
certain email is genuine.
******************************************
You
can go to jail note: If you are contemplating using fake email to commit
a crime, think again. If you are reading this
you don't know enough to forge
email well enough to elude arrest.
*******************************************
Here
is an example of a different email program, sendmail. This will give
you an idea of the small variations you'll run into
with this hack.
Here's my command:
telnet ns.Interlink.Net 25
The computer answers:
Trying 198.168.73.8...
Connected
to NS.INTERLINK.NET.
Escape character is '^]'.
220 InterLink.NET Sendmail AIX 3.2/UCB 5.64/4.03 ready at Fri, 12 Jul
1996
15:45
Then I tell it:
helo santa@north.pole.org
And it responds:
250 InterLink.NET Hello
santa@north.pole.org (plato.nmia.com)
Oh, oh! This sendmail version isn't fooled at all! See how it puts
"(plato.nmia.com)"
-- the computer I was using for this hack -- in there
just to let me know it knows from what computer I've telnetted? But
what the
heck, all Internet hosts know that kind of info. I'll just bull ahead and
send fake mail anyhow. Again, my
input has no numbers in front, while the
responses of the computer are prefaced by the number 250:
mail from:santa@north.pole.com
250
santa@north.pole.com... Sender is valid.
rcpt to:cmeinel@nmia.com
250 cmeinel@nmia.com... Recipient is valid.
data
354
Enter mail. End with the . character on a line by itself.
It works!
.
250 Ok
quit
221 InterLink.NET:
closing the connection.
OK, what kind of email did that computer generate? Here's what I saw using Pine:
Return
Path: <santa@north.pole.org>
Received:
from InterLink.NET by nmia.com
with smtp
(Linux Smail3.1.28.1
#4)
id m0ueo7t 000LEKC; Fri, 12 Jul 96 13:43 MDT
Received: from plato.nmia.com
by InterLink.NET (AIX 3.2/UCB 5.64/4.03)
id AA23900; Fri, 12 Jul
1996 15:43:20 0400
Oops. Here the InterLink.NET computer has revealed the computer I was on
when I telnetted
to its port 25. However, many people use that Internet host
computer.
Date: Fri, 12 Jul 1996 15:43:20 0400
From:
santa@north.pole.org
Message Id: <9607121943.AA23900@InterLink.NET>
Apparently To: cmeinel@nmia.com
It
worked!
OK, here it doesn't say "Apparently-From," so now I know the computer
ns.Interlink.Net is a pretty good
one to send fake mail from. An experienced
email aficionado would know from the Received: line that this is fake mail.
But
its phoniness doesn't just jump out at you.
I'm going to try another computer. Hmmm, the University of California at
Berkeley
is renowned for its computer sciences research. I wonder what their
hosts are like? Having first looked up the numerical
Internet address of one
of their machines, I give the command:
telnet 128.32.152.164 25
It responds with:
Trying
128.32.152.164...
Connected to 128.32.152.164.
Escape character is '^]'.
220 remarque.berkeley.edu ESMTP Sendmail
8.7.3/1.31 ready at Thu, 11 Jul
1996 12
help
214 This is Sendmail version 8.7.3
214 Commands:
214
HELO EHLO MAIL RCPT DATA
214
RSET NOOP QUIT HELP VRFY
214
EXPN VERB
214 For more info use "HELP <topic>".
214 To report bugs in the implementation send
email to
214 sendmail@CS.Berkeley.EDU.
214 For local information send email to Postmaster
at your site.
214 End of HELP info
Oh, boy, a slightly different sendmail program! I wonder what more it will
tell
me about these commands?
HELP mail
214 MAIL FROM: <sender>
214 Specifies the
sender.
214 End of HELP info
Big f***ing deal! Oh, well, let's see what this computer (which we now know
is
named remarque) will do to fake mail.
MAIL FROM:santa@north.pole.org
250 santa@north.pole.org... Sender ok
Heyyy...
this is interesting ... I didn't say "helo" and this sendmail
program didn't slap me on the wrist! Wonder what that means...
RCPT
TO:cmeinel@techbroker.com
250 Recipient ok
DATA
354 Enter mail, end with "." on a line by itself
This is fake
mail on a Berkeley computer for which I do not have a password.
.
250 MAA23472 Message accepted for delivery
quit
221
remarque.berkeley.edu closing connection
Now we go to Pine and see what the header looks like:
Return Path:
<santa@north.pole.org>
Received:
from nmia.com by nmia.com
with smtp
(Linux Smail3.1.28.1
#4)
id m0ueRnW 000LGiC; Thu, 11 Jul 96 13:53 MDT
Received:
from remarque.berkeley.edu by nmia.com
with smtp
(Linux Smail3.1.28.1
#4)
id m0ueRnV 000LGhC; Thu, 11 Jul 96 13:53 MDT
Apparently To: <cmeinel@techbroker.com>
Received:
from merde.dis.org by remarque.berkeley.edu (8.7.3/1.31)
id MAA23472; Thu,
11 Jul 1996 12:49:56 0700 (PDT)
Look at the three "received" messages. My ISP's computer received this email
not
directly from Remarque.berkeley.edu. but from merde.dis.com, which in
turn got the email from Remarque.
Hey, I
know who owns merde.dis.org! So the Berkeley computer forwarded this
fake mail through famed computer security expert Pete
Shipley's Internet
host computer! Hint: the name "merde" is a joke. So is "dis.org."
Now let's see what email from
remarque looks like. Let's use Pine again:
Date: Thu, 11 Jul 1996 12:49:56 0700 (PDT)
From: santa@north.pole.org
Message
Id: <199607111949.MAA23472@remarque.berkeley.edu>
This is fake mail on a Berkeley computer for which I do not
have a password.
Hey, this is pretty kewl. It doesn't warn that the Santa address is phony!
Even better, it keeps secret the name of
the originating computer:
plato.nmia.com. Thus remarque.berkeley.edu was a really good computer from
which to send fake
mail. (Note: last time I checked, they had fixed
remarque, so don't bother telnetting there.)
But not all sendmail
programs are so friendly to fake mail. Check out the
email I created from atropos.c2.org!
telnet atropos.c2.org
25
Trying 140.174.185.14...
Connected to atropos.c2.org.
Escape character is '^]'.
220 atropos.c2.org ESMTP
Sendmail 8.7.4/CSUA ready at Fri, 12 Jul 1996 15:41:33
help
502 Sendmail 8.7.4 HELP not implemented
Gee,
you're pretty snippy today, aren't you... What the heck, let's plow
ahead anyhow...
helo santa@north.pole.org
501
Invalid domain name
Hey, what's it to you, buddy? Other sendmail programs don't give a darn what
name I use with
"helo." OK, OK, I'll give you a valid domain name. But not
a valid user name!
helo satan@unm.edu
250
atropos.c2.org Hello cmeinel@plato.nmia.com [198.59.166.165], pleased
to meet you
Verrrry funny, pal. I'll just
bet you're pleased to meet me. Why the #%&@
did you demand a valid domain name when you knew who I was all along?
mail
from:santa@north.pole.com
250 santa@north.pole.com... Sender ok
rcpt to: cmeinel@nmia.com
250 Recipient ok
data
354
Enter mail, end with "." on a line by itself
Oh, crap!
.
250 PAA13437 Message accepted for delivery
quit
221
atropos.c2.org closing connection
OK, what kind of email did that obnoxious little sendmail program generate?
I
rush over to Pine and take a look:
Return Path: <santa@north.pole.com>
Well, how very nice to allow
me to use my fake address.
Received:
from atropos.c2.org by nmia.com
with smtp
(Linux Smail3.1.28.1
#4)
id m0ueqxh 000LD9C; Fri, 12 Jul 96 16:45 MDT
Apparently To: <cmeinel@nmia.com>
Received:
from satan.unm.edu (cmeinel@plato.nmia.com [198.59.166.165])
Oh, how truly special! Not only did the computer atropos.c2.org
blab out my
true identity, it also revealed that satan.unm.edu thing. Grump...
that will teach me.
by atropos.c2.org
(8.7.4/CSUA) with SMTP id PAA13437 for
cmeinel@nmia.com; Fri, 12
Jul 1996 15:44:37 0700 (PDT)
Date: Fri,
12 Jul 1996 15:44:37 0700 (PDT)
From: santa@north.pole.com
Message Id: <199607122244.PAA13437@atropos.c2.org>
Oh, crap!
So, the moral of that little hack is that there are lots of different email
programs floating around
on port 25 of Internet hosts. So if you want to
have fun with them, it's a good idea to check them out first before you
use
them to show off with.
_________________________________________________________
Want to share some kewl
stuph? Tell me I'm terrific? Flame me? For the first
two, I'm at cmeinel@techbroker.com. Please direct flames to
dev/null@techbroker.com.
Happy hacking!
Copyright 1996 Carolyn P. Meinel. You may forward the GUIDE TO (mostly)
HARMLESS HACKING as long as you
leave this notice at the end. To subscribe,
email cmeinel@techbroker.com with message "subscribe hacker
<joe.blow@boring.ISP.net>"
substituting your real email address for Joe Blow's.
________________________________________________________
