直接给了源码:
<?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><?= $message ?></p>
<?php } ?>
<form action="index.php" method="POST">
<input type="text" name="guess">
<input type="submit">
</form>
</body>
</html>
分析源码,结合过往做的爆破随机数题目的经验可以看出随机数是个幌子,直接忽略.随后百度$_SERVER['PHP_SELF']发现文章:[红日安全]代码审计Day15 – $_SERVER[‘PHP_SELF’]导致的防御失效问题
而且源码中还用到了basename(),可以获取到最后的文件名,而get请求source可以显示basename($_SERVER['PHP_SELF'])文件的内容,结合之前找到的文章构造payload,/index.php/config.php/?source.但是这里使用了正则对config.php是否为$_SERVER[‘PHP_SELF’]的结尾进行了判断,若config.php是结尾则程序结束.所以我们还需要绕过该正则.basename()函数会去掉非ascii字符,所以我们在config.php后面再加上非ascii字符然后get请求source.最终payload:/index.php/config.php/%ff?source
No responses yet