위는 natas20의 초기화면이다.
아래 코드는 View sourcecode를 통해 확인해주었다.
<html>
<head>
<!-- This stuff in the header has nothing to do with the level -->
<link rel="stylesheet" type="text/css" href="http://natas.labs.overthewire.org/css/level.css">
<link rel="stylesheet" href="http://natas.labs.overthewire.org/css/jquery-ui.css" />
<link rel="stylesheet" href="http://natas.labs.overthewire.org/css/wechall.css" />
<script src="http://natas.labs.overthewire.org/js/jquery-1.9.1.js"></script>
<script src="http://natas.labs.overthewire.org/js/jquery-ui.js"></script>
<script src=http://natas.labs.overthewire.org/js/wechall-data.js></script><script src="http://natas.labs.overthewire.org/js/wechall.js"></script>
<script>var wechallinfo = { "level": "natas20", "pass": "<censored>" };</script></head>
<body>
<h1>natas20</h1>
<div id="content">
<?php
function debug($msg) { /* {{{ */
if(array_key_exists("debug", $_GET)) {
print "DEBUG: $msg<br>";
}
}
/* }}} */
function print_credentials() { /* {{{ */
if($_SESSION and array_key_exists("admin", $_SESSION) and $_SESSION["admin"] == 1) {
print "You are an admin. The credentials for the next level are:<br>";
print "<pre>Username: natas21\n";
print "Password: <censored></pre>";
} else {
print "You are logged in as a regular user. Login as an admin to retrieve credentials for natas21.";
}
}
/* }}} */
/* we don't need this */
function myopen($path, $name) {
//debug("MYOPEN $path $name");
return true;
}
/* we don't need this */
function myclose() {
//debug("MYCLOSE");
return true;
}
function myread($sid) {
debug("MYREAD $sid");
if(strspn($sid, "1234567890qwertyuiopasdfghjklzxcvbnmQWERTYUIOPASDFGHJKLZXCVBNM-") != strlen($sid)) {
debug("Invalid SID");
return "";
}
$filename = session_save_path() . "/" . "mysess_" . $sid;
if(!file_exists($filename)) {
debug("Session file doesn't exist");
return "";
}
debug("Reading from ". $filename);
$data = file_get_contents($filename);
$_SESSION = array();
foreach(explode("\n", $data) as $line) {
debug("Read [$line]");
$parts = explode(" ", $line, 2);
if($parts[0] != "") $_SESSION[$parts[0]] = $parts[1];
}
return session_encode();
}
function mywrite($sid, $data) {
// $data contains the serialized version of $_SESSION
// but our encoding is better
debug("MYWRITE $sid $data");
// make sure the sid is alnum only!!
if(strspn($sid, "1234567890qwertyuiopasdfghjklzxcvbnmQWERTYUIOPASDFGHJKLZXCVBNM-") != strlen($sid)) {
debug("Invalid SID");
return;
}
$filename = session_save_path() . "/" . "mysess_" . $sid;
$data = "";
debug("Saving in ". $filename);
ksort($_SESSION);
foreach($_SESSION as $key => $value) {
debug("$key => $value");
$data .= "$key $value\n";
}
file_put_contents($filename, $data);
chmod($filename, 0600);
}
/* we don't need this */
function mydestroy($sid) {
//debug("MYDESTROY $sid");
return true;
}
/* we don't need this */
function mygarbage($t) {
//debug("MYGARBAGE $t");
return true;
}
session_set_save_handler(
"myopen",
"myclose",
"myread",
"mywrite",
"mydestroy",
"mygarbage");
session_start();
if(array_key_exists("name", $_REQUEST)) {
$_SESSION["name"] = $_REQUEST["name"];
debug("Name set to " . $_REQUEST["name"]);
}
print_credentials();
$name = "";
if(array_key_exists("name", $_SESSION)) {
$name = $_SESSION["name"];
}
?>
<form action="index.php" method="POST">
Your name: <input name="name" value="<?=$name?>"><br>
<input type="submit" value="Change name" />
</form>
<div id="viewsource"><a href="index-source.html">View sourcecode</a></div>
</div>
</body>
</html>
function print_credentials() { /* {{{ */
if($_SESSION and array_key_exists("admin", $_SESSION) and $_SESSION["admin"] == 1) {
print "You are an admin. The credentials for the next level are:<br>";
print "<pre>Username: natas21\n";
print "Password: <censored></pre>";
} else {
print "You are logged in as a regular user. Login as an admin to retrieve credentials for natas21.";
}
}위 코드를 통해 admin을 1로 만들어야 한다는 것을 알 수 있다. 또한 debug값을 확인할 수 있다.
url에 ?debug=true&name=admin을 추가해주었더니 아래와 같이 떴다.
admin=1임을 넣어주기 위해 &admin=1을 해보았지만 아무런 변화가 일어나지 않았다.
그래서 개행문자를 이용하여 인코딩된 문자열을 넣어주었다.
url에 ?debug=true&name=admin%0aadmin%201 을 추가해주었더니 아래와 같이 비밀번호를 얻을 수 있었다.
|89OWrTkGmiLZLv12JY4tLj2c4FW0xn56
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