Wednesday, November 14, 2007

Hacking into Unix System?

Hacking into Unix System?
I will be referring to all the UNIX variants/etc as UNIX, so when I say something about UNIX, it generally means all the variants (Unix System V variants that is: BSD, SunOS, Ultrix, Xenix, etc.), unless I state a variant in particular.

Most commonly used passwords during the remote log

ACCOUNT PASSWORD
------- --------
root root - Rarely open to hackers
sys sys / system / bin
bin sys / bin
mountfsys mountfsys
adm adm
uucp uucp
nuucp anon
anon anon
user user
games games
install install
reboot * See Below
demo demo
umountfsys umountfsys
sync sync
admin admin
guest guest
daemon daemon
Public access Unixes [like Public BBSs] will tell you how to logon if you are a new users. Unfortunatly, this phile is not about public access Unixes, but I will talk about them briefly later, as a UUCP/UseNet/Bitnet address for mail. OK. You've gotten to the login prompt! Now, what you need to do here is enter in a valid account. An Account usually consists of 8 characters or less. After you enter in an account, you will probably get a password prompt of some sort. The prompts may vary, as the source code to the login program is usually supplied with UNIX, or is readily available for free. Well, The easiest thing I can say to do to login is basically this: Get an account, or try the defaults. The defaults are ones that came with the operating system, in standard form. The accounts root, mountfsys, umountfsys, install, and sometimes sync are root level accounts, meaning they have sysop power, or total power.

The REBOOT login is what as known as a command login, which just simply doesn't let you into the operating system, but executes a program assigned to it. It usually does just what it says, reboot the system.
COMMAND LOGINS

There are "command logins", which, like reboot, execute a command then log you off instead of letting you use the command interpreter. BSD is notorious for having these, and concequently, so does MIT's computers. Here are some:

rwho - show who is online
finger - same
who - same
These are the most useful, since they will give the account names that are online, thus showing you several accounts that actually exist. When you get an invalid Account name / invalid password, or both, you will get some kind of error. Usually it is the "login incorrect" message. When the computer tells you that, you have done something wrong by either entering an invalid account name, or a valid account name, but invalid password. It does not tell you which mistake you made, for obvious reasons. Also, when you login incorrectly, the error log on the system gets updated, letting the sysops(s) know something is a miss.

Another error is "Cannot change to home directory" or "Cannot Change Directory." This means that no "home directory" which is essentially the 'root' directory for an account, which is the directory you start off in. On DOS, you start in A:\ or C:\ or whatever, but in UNIX you start in /homedirectory. [Note: The / is used in directories on UNIX, not a \ ]. Most systems will log you off after this, but some tell you that they will put you in the root directory [ '/'].

Another error is "No Shell". This means that no "shell" was defined for that particular account. The "shell" will be explained later. Some systems will log you off after this message. Others will tell you that they will use the regular shell, by saying "Using the bourne shell", or "Using sh"
User structure in the UNIX environment.

Think of UNIX having two levels of security: absolute power, or just a regular user. The ones that have absolute power are those users at the root level. Ok, now is the time to think in numbers. Unix associates numbers with account names. each account will have a number. Some will have the same number. That number is the UID [user-id] of the account. the root user id is 0. Any account that has a user id of 0 will have root access. Unix does not deal with account names (logins) but rather the number associated with them. for instance, If my user-id is 50, and someone else's is 50, with both have absolute power of each other, but no-one else.

A shell is an executable program which loads and runs when a user logs on, and is in the foreground. This "shell" can be any executable program, and it is defined in the "passwd" file which is the userfile. Each login can have a unique "shell". Ok. Now the shell that we usually will work with is a command interpreter. A command interpreter is simply something like MSDOS's COMMAND.COM, which processes commands, and sends them to the kernel [operating system]. A shell can be anything, as I said before,
but the one you want to have is a command interpreter. Here are the usual shells you will find:

sh - This is the bourne shell. It is your basic Unix "COMMAND.COM". It has
a "script" language, as do most of the command interpreters on Unix systems
csh - This is the "C" shell, which will allow you to enter "C" like commands.
ksh - this is the korn shell. Just another command interpreter.
tcsh - this is one, which is used at MIT I believe. Allows command editing.
vsh - visual shell. It is a menu driven deal. Sorta like.. Windows for DOS
rsh - restricted shell OR remote shell.

EVERYTHING in Unix is CASE sensitive. This means "Hill" and "hill" are not the same thing. This allows for many files to be able to be stored, since "Hill" "hill" "hIll" "hiLl", etc. can be different files. So, when using the [] stuff, you have to specify capital letters if any files you are dealing with has capital letters. Most everything is lower case though

Commands to use?

ls - this is to get a directory. With no arguments, it will just print out
file names in either one column or multi-column output, depending on the
ls program you have access to.

example:
$ ls
hithere
runme
note.text
src
$
the -l switch will give you extended info on the files.
$ ls -l
rwx--x--x sirhack sirh 10990 runme
and so on....

the "rwx--x--x" is the file permission.
the "rwx--x--x" is the file permission. [Explained Later]
the "sirhack sirh" is the owner of the file/group the file is in.
sirhack = owner, sirh = user-group the file is in [explained later]
the 10990 is the size of the file in bytes.
"runme" is the file name.

cat - this types out a file onto the screen. should be used on text files.
only use it with binary files to make a user mad [explained later]
ex:
$ cat note.txt
This is a sample text file!
$

cp - this copies a file. syntax for it is "cp fromfile tofile"
$ cp runme runme2
$ ls
hithere
runme
note.text
src
runme2
Full pathnames can be included, as to copy it to another directory.
$ cp runme /usr/datwiz/runme

mv - this renames a file. syntax "mv oldname newname"
$ mv runme2 runit
$ ls
hithere
runme
note.text
src
runit
files can be renamed into other directories.
$ mv runit /usr/datwiz/run
$ ls
hithere
runme
note.text
src
$ ls /usr/datwiz
runme
run

pwd - gives current directory
$ pwd
/usr/sirhack
$ cd src
$ pwd
/usr/sirhack/src
$ cd ..
$ pwd
/usr/sirhack
[ the ".." means use the name one directory back. ]
$ cd ../datwiz
[translates to cd /usr/datwiz]
$ pwd
/usr/datwiz
$ cd $home
[goto home dir]
$ pwd
/usr/sirhack

rm - delete a file. syntax "rm filename" or "rm -r directory name"
$ rm note.text
$ ls
hithere
runme
src
$

write - chat with another user. Well, "write" to another user.
syntax: "write username"
$ write scythian
scythian has been notified
Hey Scy! What up??
Message from scythian on tty001 at 17:32
hey!
me: So, hows life?
scy: ok, I guess.
me: gotta go finish this text file.
scy: ok
me: control-D [to exit program]
$
mesg - turn write permissions on or off to your terminal (allow chat)
format "mesg y" or "mesg n"
cc - the C compiler. don't worry about this one right now.
chmod - change mode of a file. Change the access in other words.
syntax: "chmod mode filename"
$ chmod a+r newtext
Now everyone can read newtext.
a = all
r = read. This will be explained further in the File System section.

chown - change the owner of a file.
syntax: "chown owner filename"
$ chown scythian newtext
$
chgrp - change the group [explained later] of a file.
syntax: "chgrp group file"
$ chgrp root runme
$
finger - print out basic info on an account. Format: finger username
grep - search for patterns in a file. syntax: "grep pattern file"
$ grep 1 newtext
This is Line 1
$ grep THE newtext
This is THE first line
$ grep "THE line 1" newtext
$

mail - This is a very useful utility. Obviously, you already know what it
is by its name. There are several MAIL utilities, such as ELM, MUSH
and MSH, but the basic "mail" program is called "mail". The usage
is:
"mail username@address" or
"mail username"
or
"mail"
or "mail addr1!addr2!addr3!user"

"mail username@address" - This is used to send mail to someone on
another system, which is usually another UNIX, but some DOS machines and some
VAX machines can recieve Unix Mail. When you use "mail user@address" the
system you are on MUST have a "smart mailer" [known as smail], and must
have what we call system maps. The smart mailer will find the "adress" part
of the command and expand it into the full pathname usually. I could look
like this: mail phiber@optik

might have seen the mail bombing in the die hard 4 [
ps - process. This command allows you to see what you are actually doing
in memory. Everytime you run a program, it gets assigned a Process Id number
(PID), for accounting purposes, and so it can be tracked in memory, as
well as shut down by you, or root. usually, the first thing in a process
list given by "ps" is your shell name. Say I was logged in under sirhack,
using the shell "csh" and running "watch scythian". The watch program would
go into the background, meaning I'd still be able to do things while it was
running:
$ ps
PID TTY NAME
122 001 ksh
123 001 watch
$
That is a shortened PS. That is the default listing [a brief one].
The TTY column represents the "tty" [i/o device] that the process is being
run from. This is only useful really if you are using layers (don't worry)
or more than one person is logged in with the same account name. Now,
"ps -f" would give a full process listing on yourself, so instead of
seeing just plain ole "watch" you'd most likely see "watch scythian"
kill - kill a process. This is used to terminate a program in memory obvio-
ously. You can only kill processes you own [ones you started], unless you
are root, or your EUID is the same as the process you want to kill.
(Will explain euid later). If you kill the shell process, you are logged
off. By the same token, if you kill someone else's shell process, they
are logged off. So, if I said "kill 122" I would be logged off. However,
kill only sends a signal to UNIX telling it to kill off a process. If
you just use the syntax "kill pid" then UNIX kills the process WHEN it feels
like it, which may be never. So, you can specify urgency! Try "kill -num pid"
Kill -9 pid is a definite kill almost instantly. So if I did this:
$ kill 122
$ kill 123
$ ps
PID TTY NAME
122 001 ksh
123 001 watch
$ kill -9 123
[123]: killed

you can do "kill -1 0" to kill your shell process to log yourself off.
This is useful in scripts (will be explained later).

HACKING UNIX SYSTEM?????????????????????????

The first step in hacking a UNIX is to get into the operating system
by finding a valid account/password. The object of hacking is usually to
get root (full privileges), so if you're lucky enough to get in as root,
you need not read anymore of this hacking phile , and get into the
"Having Fun" Section. Hacking can also be just to get other's accounts also.

Getting IN
----------
The first thing to do is to GET IN to the Unix. I mean, get past
the login prompt. That is the very first thing. When you come across a UNIX,
sometimes it will identify itself by saying something like,
"Young INC. Company UNIX"
or Just
"Young Inc. Please login"

Here is where you try the defaults I listed. If you get in with those
you can get into the more advanced hacking (getting root). If you do something
wrong at login, you'll get the message
"login incorrect"
This was meant to confuse hackers, or keep the wondering. Why?
Well, you don't know if you've enterred an account that does not exist, or one
that does exist, and got the wrong password. If you login as root and it says
"Not on Console", you have a problem. You have to login as someone else,
and use SU to become root.

Now, this is where you have to think. If you cannot get in with a
default, you are obviously going to have to find something else to
login as. Some systems provide a good way to do this by allowing the use
of command logins. These are ones which simply execute a command, then
logoff. However, the commands they execute are usually useful. For instance
there are three common command logins that tell you who is online at the
present time. They are:
who
rwho
finger

If you ever successfully get one of these to work, you can write down
the usernames of those online, and try to logon as them. Lots of unsuspecting
users use there login name as their password. For instance, the user
"bob" may have a password named "bob" or "bob1". This, as you know, is
not smart, but they don't expect a hacking spree to be carried out on
them. They merely want to be able to login fast.
If a command login does not exist, or is not useful at all, you will
have to brainstorm. A good thing to try is to use the name of the unix
that it is identified as. For instance, Young INC's Unix may have an account
named "young"
Young, INC. Please Login.
login: young
UNIX SYSTEM V REL 3.2
(c)1984 AT&T..
..
..
..

Some unixes have an account open named "test". This is also a default,
but surprisingly enough, it is sometimes left open. It is good to try to
use it. Remember, brainstorming is the key to a unix that has no apparent
defaults open. Think of things that may go along with the Unix. type
in stuff like "info", "password", "dial", "bbs" and other things that
may pertain to the system. "att" is present on some machines also.

ONCE INSIDE -- SPECIAL FILES
There are several files that are very important to the UNIX
environment. They are as follows:

/etc/passwd - This is probably the most important file on a Unix. Why?
well, basically, it holds the valid usernames/passwords.
This is important since only those listed in the passwd
file can login, and even then some can't (will explain).
The format for the passwordfile is this:

username:password:UserID:GroupID:description(or real name):homedir:shell

Here are two sample entries:

sirhack:89fGc%^7&a,Ty:100:100:Sir Hackalot:/usr/sirhack:/bin/sh
demo::101:100:Test Account:/usr/demo:/usr/sh
In the first line, sirhack is a valid user. The second
field, however, is supposed to be a password, right? Well,
it is, but it's encrypted with the DES encryption standard.
the part that says "&a,Ty" may include a date after the comma
(Ty) that tells unix when the password expires. Yes, the
date is encrypted into two alphanumeric characters (Ty).

In the Second example, the demo account has no password.
so at Login, you could type in:

login: demo
UNIX system V
(c)1984 AT&T
..
..

But with sirhack, you'd have to enter a password. Now,
the password file is great, since a lot of times, you;ll
be able to browse through it to look for unpassworded
accounts. Remember that some accounts can be restricted
from logging in, as such:

bin:*:2:2:binaccount:/bin:/bin/sh

The '*' means you won't be able to login with it. Your
only hope would be to run an SUID shell

Remember that some accounts can be restricted
from logging in, as such:

bin:*:2:2:binaccount:/bin:/bin/sh

The '*' means you won't be able to login with it. Your
only hope would be to run an SUID shell (explained later).
note about the DES encryption: each unix makes its own unique "keyword" to base encryption off of. Most of the time its just random letters and numbers. Its chosen at installation time by the operating system. Now, decrypting DES encrypted things ain't easy. Its pretty much impossible. Especially decrypting the password file (decrypting the password field within the password file to be exact). Always beware a hacker who
says he decrypted a password file. He's full of shit. Passwords are never decrypted on unix, but rather, a system call is made to a function called "crypt" from within the C language, and the string you enter as the password gets encrypted, and compared to the encrypted password. If they match, you're in. Now, there are password hackers, but they do not decrypt the password file, but rather, encrypt words from a dictionary
and try them against every account (by crypting/comparing) until it finds a match (later on!). Remember, few, if none, have decrypted the password file successfully