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[Webhacking.kr] Challenge Old 6 - 문제풀이 본문

정보보안/워게임

[Webhacking.kr] Challenge Old 6 - 문제풀이

Ye0ngJae 2022. 12. 21. 10:33
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문제

 

 

 

 

풀이

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우선 view-source 버튼을 눌러 페이지의 소스코드를 확인하여 보자. 

 

<?php
include "../../config.php";
if($_GET['view_source']) view_source();
if(!$_COOKIE['user']){
  $val_id="guest";
  $val_pw="123qwe";
  for($i=0;$i<20;$i++){
    $val_id=base64_encode($val_id);
    $val_pw=base64_encode($val_pw);
  }
  $val_id=str_replace("1","!",$val_id);
  $val_id=str_replace("2","@",$val_id);
  $val_id=str_replace("3","$",$val_id);
  $val_id=str_replace("4","^",$val_id);
  $val_id=str_replace("5","&",$val_id);
  $val_id=str_replace("6","*",$val_id);
  $val_id=str_replace("7","(",$val_id);
  $val_id=str_replace("8",")",$val_id);

  $val_pw=str_replace("1","!",$val_pw);
  $val_pw=str_replace("2","@",$val_pw);
  $val_pw=str_replace("3","$",$val_pw);
  $val_pw=str_replace("4","^",$val_pw);
  $val_pw=str_replace("5","&",$val_pw);
  $val_pw=str_replace("6","*",$val_pw);
  $val_pw=str_replace("7","(",$val_pw);
  $val_pw=str_replace("8",")",$val_pw);

  Setcookie("user",$val_id,time()+86400,"/challenge/web-06/");
  Setcookie("password",$val_pw,time()+86400,"/challenge/web-06/");
  echo("<meta http-equiv=refresh content=0>");
  exit;
}
?>
<html>
<head>
<title>Challenge 6</title>
<style type="text/css">
body { background:black; color:white; font-size:10pt; }
</style>
</head>
<body>
<?php
$decode_id=$_COOKIE['user'];
$decode_pw=$_COOKIE['password'];

$decode_id=str_replace("!","1",$decode_id);
$decode_id=str_replace("@","2",$decode_id);
$decode_id=str_replace("$","3",$decode_id);
$decode_id=str_replace("^","4",$decode_id);
$decode_id=str_replace("&","5",$decode_id);
$decode_id=str_replace("*","6",$decode_id);
$decode_id=str_replace("(","7",$decode_id);
$decode_id=str_replace(")","8",$decode_id);

$decode_pw=str_replace("!","1",$decode_pw);
$decode_pw=str_replace("@","2",$decode_pw);
$decode_pw=str_replace("$","3",$decode_pw);
$decode_pw=str_replace("^","4",$decode_pw);
$decode_pw=str_replace("&","5",$decode_pw);
$decode_pw=str_replace("*","6",$decode_pw);
$decode_pw=str_replace("(","7",$decode_pw);
$decode_pw=str_replace(")","8",$decode_pw);

for($i=0;$i<20;$i++){
  $decode_id=base64_decode($decode_id);
  $decode_pw=base64_decode($decode_pw);
}

echo("<hr><a href=./?view_source=1 style=color:yellow;>view-source</a><br><br>");
echo("ID : $decode_id<br>PW : $decode_pw<hr>");

if($decode_id=="admin" && $decode_pw=="nimda"){
  solve(6);
}
?>
</body>
</html>

 

코드는 크게 base64 인코딩을 하여 쿠키 값에 저장을 하는 부분과 쿠키 값을 base64 디코딩하여 아래 조건문을 통해 비교를 하는 부분으로 나눌 수 있다. 

 

우선 base64 인코딩 부분을 살펴보자면, var_id와 var_pw 값을 20번정도 base64 인코딩 한 후에 특수문자들을 각각 다른 숫자로 치환하는 것을 확인할 수 있다. 이렇게 인코딩과 문자열 치환작업을 거친 var_id와 var_pw 값은 password와 user 쿠키에 저장되게 된다. 

 

다음으로 base64 디코딩 부분을 살펴보자면 아까 문자열을 base64 인코딩 한 코드의 역순으로 다시 디코딩하는 것을 확인할 수 있다. 따라서 위 코드의 base64 인코딩 부분 코드를 따로 작성하여 var_id와 var_pw 값을 아래 조건문에서 비교하는 값인 admin과 nimda로 변경해주면 될 것 같다. 

 

import base64

userid = 'admin'
userpw = 'nimda'
  
userid = userid.encode('ascii')
userpw = userpw.encode('ascii')

for i in range(0,20):
  userid = base64.b64encode(userid)
  userpw = base64.b64encode(userpw)
    
userid = userid.decode('ascii')
userpw = userpw.decode('ascii')

userid.replace('1','!')
userid.replace('2','@')
userid.replace('3','$')
userid.replace('4','^')
userid.replace('5','&')
userid.replace('6','*')
userid.replace('7','(')
userid.replace('8',')')

userpw.replace('1','!')
userpw.replace('2','@')
userpw.replace('3','$')
userpw.replace('4','^')
userpw.replace('5','&')
userpw.replace('6','*')
userpw.replace('7','(')
userpw.replace('8',')')
  
print(userid)
print(userpw)

 파이썬을 이용하여 base64 인코딩 부분을 작성하였다. 그리고 해당 코드를 실행하면 

 

Vm0wd2QyUXlVWGxWV0d4V1YwZDRWMVl3WkRSV01WbDNXa1JTVjAxV2JETlhhMUpUVmpBeFYySkVUbGhoTVVwVVZtcEJlRll5U2tWVWJHaG9UVlZ3VlZadGNFSmxSbGw1VTJ0V1ZXSkhhRzlVVmxaM1ZsWmFjVkZ0UmxSTmJFcEpWbTEwYTFkSFNrZGpSVGxhVmpOU1IxcFZXbUZrUjA1R1UyMTRVMkpIZHpGV1ZFb3dWakZhV0ZOcmFHaFNlbXhXVm1wT1QwMHhjRlpYYlVaclVqQTFSMWRyV25kV01ERkZVbFJHVjFaRmIzZFdha1poVjBaT2NtRkhhRk5sYlhoWFZtMXdUMVF3TUhoalJscFlZbGhTV0ZSV2FFTlNiRnBZWlVaT1ZXSlZXVEpWYkZKRFZqQXhkVlZ1V2xaaGExcFlXa1ZhVDJOc2NFZGhSMnhUVFcxb2IxWXhaREJaVmxsM1RVaG9hbEpzY0ZsWmJGWmhZMnhXY1ZGVVJsTk5WMUo1VmpKNFQxWlhTbFpYVkVwV1lrWktTRlpxUm1GU2JVbDZXa1prYUdFeGNHOVdha0poVkRKT2RGSnJhR2hTYXpWeldXeG9iMWRHV25STldHUlZUVlpHTTFSVmFHOWhiRXB6WTBac1dtSkdXbWhaTVZwaFpFZFNTRkpyTlZOaVJtOTNWMnhXWVZReFdsaFRiRnBZVmtWd1YxbHJXa3RUUmxweFVtMUdVMkpWYkRaWGExcHJZVWRGZUdOSE9WZGhhMHBvVmtSS1QyUkdTbkpoUjJoVFlYcFdlbGRYZUc5aU1XUkhWMjVTVGxOSGFGQlZiVEUwVmpGU1ZtRkhPVmhTTUhCNVZHeGFjMWR0U2tkWGJXaGFUVzVvV0ZreFdrZFdWa3B6VkdzMVYySkdhM2hXYTFwaFZURlZlRmR1U2s1WFJYQnhWVzB4YjFZeFVsaE9WazVPVFZad2VGVXlkREJXTVZweVkwWndXR0V4Y0ROV2FrWkxWakpPU1dKR1pGZFNWWEJ2Vm10U1MxUXlUWGxVYTFwb1VqTkNWRmxZY0ZkWFZscFlZMFU1YVUxcmJEUldNalZUVkd4a1NGVnNXbFZXYkhCWVZHdGFWbVZIUmtoUFYyaHBVbGhDTmxkVVFtRmpNV1IwVTJ0a1dHSlhhR0ZVVnpWdlYwWnJlRmRyWkZkV2EzQjZWa2R6TVZZd01WWmlla1pYWWxoQ1RGUnJXbEpsUm1SellVWlNhVkp1UW5oV1YzaHJWVEZzVjFWc1dsaGlWVnBQVkZaYWQyVkdWWGxrUkVKWFRWWndlVmt3V25kWFIwVjRZMFJPV21FeVVrZGFWM2hIWTIxS1IxcEhiRmhTVlhCS1ZtMTBVMU14VlhoWFdHaFlZbXhhVjFsc1pHOVdSbXhaWTBaa2JHSkhVbGxhVldNMVlWVXhXRlZyYUZkTmFsWlVWa2Q0YTFOR1ZuTlhiRlpYWWtoQ1NWWkdVa2RWTVZwMFVtdG9VRll5YUhCVmJHaERUbXhrVlZGdFJtcE5WMUl3VlRKMGExZEhTbGhoUjBaVlZucFdkbFl3V25OT2JFcHpXa2R3YVZORlNrbFdNblJyWXpGVmVWTnVTbFJpVlZwWVZGYzFiMWRHWkZkWGJFcHNVbTFTZWxsVldsTmhWa3AxVVd4d1YySllVbGhhUkVaYVpVZEtTVk5zYUdoTk1VcFZWbGN4TkdReVZrZFdiR1JvVW5wc2IxUldXbmRsYkZsNVkwVmtWMDFFUmpGWlZXaExWMnhhV0ZWclpHRldNMmhJV1RJeFMxSXhjRWhpUm1oVFZsaENTMVp0TVRCVk1VMTRWbGhvV0ZkSGFGbFpiWGhoVm14c2NscEhPV3BTYkhCNFZrY3dOVll4V25OalJXaFlWa1UxZGxsV1ZYaFhSbFp5WVVaa1RtRnNXbFZXYTJRMFdWWktjMVJ1VG1oU2JGcFlXV3hhUm1ReFduRlJiVVphVm0xU1NWWlhkRzloTVVwMFlVWlNWVlpXY0dGVVZscGhZekZ3UlZWdGNFNVdNVWwzVmxSS01HRXhaRWhUYkdob1VqQmFWbFp0ZUhkTk1WcHlWMjFHYWxacmNEQmFSV1F3VmpKS2NsTnJhRmRTTTJob1ZrUktSMVl4VG5WVmJFSlhVbFJXV1ZaR1l6RmlNV1JIWWtaV1VsZEhhRlJVVm1SVFpXeHNWbGRzVG1oU1ZFWjZWVEkxYjFZeFdYcFZiR2hZVm14d1lWcFZXbXRrVmtwelZtMXNWMUl6YURWV01XUXdXVmRSZVZaclpGZGliRXB5Vld0V1MySXhiRmxqUldSc1ZteEtlbFp0TURWWFIwcEhZMFpvV2sxSGFFeFdNbmhoVjBaV2NscEhSbGROTW1oSlYxUkplRk14U1hoalJXUmhVbXMxV0ZZd1ZrdE5iRnAwWTBWa1dsWXdWalJXYkdodlYwWmtTR0ZHV2xwaVdHaG9WbTE0YzJOc1pISmtSM0JUWWtad05GWlhNVEJOUmxsNFYyNU9hbEpYYUZoV2FrNVRWRVpzVlZGWWFGTldhM0I2VmtkNFlWVXlTa1pYV0hCWFZsWndSMVF4V2tOVmJFSlZUVVF3UFE9PQ==
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

 

base64 인코딩된 userid 값과 userpw 값을 확인할 수 있다. 해당 base64 문자열을 문제의 쿠키 값으로 넣어주면. 문제가 풀리는 것을 확인할 수 있다. 

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