hacking on Telnet explained

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					Telnet: the Number One Hacker Tool


In this Guide you will learn:

      What is telnet?

      How to telnet

      How to get telnet accounts <begin11c.shtml>

      Why you might not want to telnet <begin11c.shtml>

      How to install a telnet server on your home Windows computer <begin11c.shtml>

      How to turn off a telnet server on your home Linux computer <begin11d.shtml>

      How to explore computers using telnet <begin11d.shtml>

      Why not use a portscanner instead? <begin11f.shtml>

      How to break into web sites using telnet <begin11f.shtml>
"Where do I type that command?" People ask that all the time when they read my early Guides to
(mostly) Harmless Hacking. I wrote those guides back when the Internet was in its infancy and
almost everyone in cyberspace used telnet. However, nowadays you might never even hear about
telnet, much less use it, unless you are a hacker. So if you are still wondering about telnet, today
is your lucky day.

What Is Telnet?
Telnet is a protocol that is most commonly used to log into a remote computer. It also is the
single most powerful hacking tool on the planet. With just a telnet client program, you can:

      send email

      download source code from web sites

      send unexpected input to webservers that can give you amazing and sometimes illegal
       results

      give arbitrary input to many other services on Internet host computers

      probe the services offered by servers, routers and even people's home computers.

How to Telnet
Don't know how to telnet? Click the easy telnet links at happyhacker.com and land in the middle
of a real hacker wargame! This should work regardless of your computer operating system -- if
you have an up to date browser, if your online service provider gives you a true Internet
connection, and if your computer is able to telnet at all.
Did those links get you into a telnet session? Were you able to login to a remote computer? If
yes, congratulations.
If not, how can you fix the problem? If no telnet program appeared on your monitor when you
clicked these links, perhaps your browser is too ancient to allow telnet. Try installing the latest
Netscape browser (<http://www.netscape.com/>). Or, perhaps your operating system does not
include a telnet program. In that case, install or reinstall Windows 95 or 98. If you own a Mac,
get the superb Mac OS X or Linux PPC (<http://www.linuxppc.com/>).
If a telnet program came up and failed to connect, possibly the computer you were trying to
telnet into was down or just plain no longer in existence. Or, you may be using America Online
(or a similar extremely poor online service). If so, your simplest solution may be to get a better
online service provider. Determined to hack using AOL? See http://happyhacker.org/aol.shtml
<../aol.shtml> for some ways to make AOL give you a true Internet connection.
OK, so you've managed to telnet for the first time. Presumably you don't want to limit yourself to
telnet links on web sites. How do you telnet anywhere you want to go?
If you have Linux or any other type of Unix (BSD, SCO, Solaris, Sun OS, Irix, Ultrix, etc.)
telneting is easy. Just bring up "console" or "shell" (or whatever your GUI calls the command
line interface). At the prompt type:
telnet <hostname or IP address>

More on Telnet: the Number One Hacker Tool
Windows 2000 works pretty much like Unix. See Figure 1 for an example of a Win 2000 telnet
login. Not shown on the screen was the command "telnet 10.0.0.10", which I gave at the
Command (MS-DOS) prompt.
Figure 1: Telnet using Windows 2000
If you have Windows 95, 98 or NT, to telnet, bring up the MS-DOS prompt (Start --> Programs
--> MS-DOS).

Click "connect" then "remote system…". In the host name box place the host name or IP address
of the computer to which you wish to telnet. Leave the Port and Term Type boxes alone for now.
Here is a really important point. Every day people email me complaining that some computer
won't let them telnet into it. They ask what they are doing wrong. They aren't doing anything
wrong:

      Maybe the computer they are trying to reach no longer exists.

      Maybe the computer they are trying to reach doesn't allow telnet logins. For example,
       whois.internic.net no longer allows telnet logins on port 23 (the default port). Click here
       to learn how to telnet into whois.internic.net on the right port for that particular server.
       <../whois.shtml>

      Maybe a firewall is blocking them.

      Or maybe they make a telnet connection and the remote computer asks for a user name
       and password they don't have. Then they email me asking for how to get a login name
       and password that will work.
Newbie note: The owners or administrators of any Internet host computer decide who gets user
names and passwords. Believe it or not, about once a week someone emails me asking what user
name and password their own online service provider has assigned them for a telnet login. That's
why I'm telling people the obvious -- if you want to telnet into any computer, and you don't have
a user name and password, you must ask the owner, administrator of tech support for that system
for a user name and password. If they won't give that to you, they don't want you to have it!

You can go to jail warning: If you guess the user name and password, or use a computer
breakin technique to get or create them, or if someone other than an owner or administrator
or a legitimate user on that system gives you a user name and password, it is against the law to
use them. Many computer criminals give out user names and passwords that they obtained
illegally.

More on Telnet: the Number One Hacker Tool
How to Get Telnet Accounts
OK, so you want to get legal user names and passwords so you can telnet into other computers.
Here are some of the best ways:

      See http://happyhacker.org/links2.shtml#shells <../links2.shtml> for organizations that
       will give you free shell accounts. You can telnet into these.

      Ask Internet Service Providers for shell accounts. Some offer them, although most don't.

      Set up a telnet server on your own computer (see instructions below). Yes, once you are
       running a telnet server, you can telnet from your computer back into your computer.
       Simply give the command "telnet 127.0.0.1".

      Make friends with people who run Internet computers with telnet servers.

Why you May Not Want to Telnet
If you love your shell account server, don't ever, ever telnet or ftp into it. I recommend Ssh or
Openssh for logging into remote computers? The telnet (and ftp) protocol is a "clear text"
transmission. That means that computer on the same LAN as either You or your destination
computer, or any computer on any LAN or network path through which your connection passes
can steal your login name, password or anything else that goes across your connection. Ssh and
OpenSsh encrypt all communications so no one can snoop on you.

How to Install a Telnet Server on your Windows Computer
Usually you can't telnet into a Windows home computer. The reason is, they aren't running telnet
servers. Here's how to get a telnet server on your home Windows computers so your friends and
you can telnet in and play.
For Windows NT, the Options Pack includes a primitive telnet server.
For Windows 95/98/NT and 2000, you also can install shareware or commercial telnet servers.
Check out http://www.winfiles.com, or do a web search.
Of course installing a telnet server makes your computer vulnerable to all sorts of trouble from
hackers. It's your funeral, don't come crying top me if a telnet visitor destroys your computer

More on Telnet: the Number One Hacker Tool
How to Turn off a Telnet Server on your Unix-type Computer
If you go online with Linux or other Unix-type computer, a telnet server is the easiest way to
ensure you get destroyed by a malicious hacker. Here's how to prevent this. On most of these, the
file /etc/inetd.conf launches most of your servers. Edit the file to put a "#" in front of the line that
has telnet in it and either reboot your computer or kill and restart inetd.
If your computer doesn't use inetd to launch services, you should be able to find telnetd under
/etc/init.d.
Install ssh instead and only use that to log into your shell account.

How to Explore Computers Using Telnet
Even if a computer doesn't have a telnet server, there are lots of fun and even legal things to do
to it using telnet. The easiest thing to do is extract "banners" from a victim computer. A banner is
a message a computer will often give when you telnet to a port that is running an Internet server
of some sort.
For example, most mail sending servers use port 25. To telnet to port 25 from Win 2000 or a
Unix shell, simply type:
telnet <hostname or IP address> 25
Windows 95, 98 and NT make it a tiny bit harder.


More on Telnet: the Number One Hacker Tool
If the victim computer is running a mail server, you will see something that looks like this:
Whoa, look at that! The victim computer told us what operating system (Windows NT) and mail
server (Mercur) it runs!
A quick search of the Bugtraq archives at <http://www.securityfocus.com/> revealed horrid
things a criminal could do to that Mercur mail server. Since I think it is more fun to be nice, I
told someone at the company using this mail server about the problems. He invited me to
vacation at his beautiful Swiss home, where he and his wife keep horses and take long trail rides
in the Alps. Golly, that is much more fun than breaking into a computer!
Right about now some elite ueberhaxorz are probably reading this and saying "What a lamer
Meinel is! We can do the same thing by running nmap."
They are right, you can learn the same things by running a port scanning program such as nmap
(available at <http://www.insecure.org/>). However, I am quite careful about under what
circumstances I run any port scanner. In order to get information on what programs are running
on what ports, you must run a port scanner in a mode that will probably convince the owner of
the victim computer that you are a criminal. He or she may persuade your online service provider
to cancel your account.
The other reason to analyze computers using telnet is that you learn more. It's the difference
between eating at McDonalds and learning how to cook.



More on Telnet: the Number One Hacker Tool
A quick search of the Bugtraq archives at <http://www.securityfocus.com/> revealed horrid
things a criminal could do to that Mercur mail server. Since I think it is more fun to be nice, I
told someone at the company using this mail server about the problems. He invited me to
vacation at his beautiful Swiss home, where he and his wife keep horses and take long trail rides
in the Alps. Golly, that is much more fun than breaking into a computer!
Right about now some elite ueberhaxorz are probably reading this and saying "What a lamer
Meinel is! We can do the same thing by running nmap."
They are right, you can learn the same things by running a port scanning program such as nmap
(available at <http://www.insecure.org/>). However, I am quite careful about under what
circumstances I run any port scanner. In order to get information on what programs are running
on what ports, you must run a port scanner in a mode that will probably convince the owner of
the victim computer that you are a criminal. He or she may persuade your online service provider
to cancel your account.
The other reason to analyze computers using telnet is that you learn more. It's the difference
between eating at McDonalds and learning how to cook.

How to Break into Web Sites Using Telnet
You don't have to use a web browser to access files on a web site. All you need to do is:
telnet <victimcomputer> 80
Or specify port 80 in a Windows telnet.
If you are using Windows 95/98/NT, whenever you are NOT logging into a telnet account, you
should enable local echo. Otherwise whatever you type in (unless you are in a telnet account)
will not show on the screen. To enable local echo, click Terminal --> Preferences --> Local
Echo.
So how do you send stuff back to the webserver? Try this:
GET / HTTP/1.0
<your command here>
What kinds of commands can you send? The book Hackproofing Your Network
<../bookstore/general.shtml> (by Ryan Russell of Securityfocus.com and Stance Cunningham)
suggests a fun and harmless hack. Create and store a bogus cookie in the location on your web
browser that stores cookies. (Find it by searching for the file "cookies.txt".) Name your bogus
cookie something like "MyBogusCookie." Then telnet to the victim webserver and give
something like this command:
GET / HTTP/1.0
User-Agent: HaveABogusCookieThisIsAJoke 123.4
Cookie: /; MyBogusCookie
The Überhacker! -- How to Break into Computers <../uberhacker/index.shtml> book details a
number of serious attacks you can perform through sending funny input to a webserver.
Basically, you need to learn how to write shell programs, and then find ways to get them to be
run by the webserver. I'm not going to explain them here, however. These attacks, when carried
out against a vulnerable webserver, are so easy that little kids could do them, and I don't want to
be responsible for their behavior. It's much harder for little kids to get a hold of Russell's and my
books than it is for them to read this GTMHH on the Happy Hacker website.
So are you dying to know what to send a webserver in order to break into it, without having to
buy a book? Here are some hints. How to do this will depend on what webserver it is, what
operating system it runs on, whether its security weaknesses have been fixed, and whether the
web designer has used things such as Common Gateway Interface (CGI) or Server Side Includes
(SSIs) that have weaknesses in them.
You will have to research these issues at Web sites that archive vulnerabilities and exploits such
as <http://www.securityfocus.com/> and <http://packestorm.securify.com/>. You will need to
study web site programming (HTML -- hypertext markup language, CGI and SSIs) and shell
programming. You will need to learn webserver commands (documented at
<http://www.w3.org/hypertext/WWW/markup/Markup.html>). You will have to use your brain
and be persistent.
But at least if you come across a telnet exploit, now you know the answer to the question "where
do I type that command?"

				
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