深入解析：BUUCTF在线评测-练习场-WebCTF习题[BSidesCF 2020]Had a bad day1-flag获取、解析

解题思路

打开靶场，作者对我们进行了亲切的关怀

老规矩查看源码、抓包并没有发现什么猫腻

点下面两个按钮会出现猫猫狗狗的图片，此时我们发现url多了个 参数category

那么比较明显就是提示我们是任意文件包含、任意文件读取漏洞了

找不到任何信息，只能知道有个index.php，那么我们尝试 伪协议读取index.php

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

 可以看到报错了

这里需要心细一点，看报错信息

include(php://filter/convert.base64-encode/resource=index.php.php)

 我们填了Index.php，怎么读的是index.php.php？

很明显，后端自动添加了.php，那么我们去掉.php试试

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

成功读取

打开源码复制全部base64编码

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解码：

Had a bad day?
Had a bad day?
Cheer up!
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!

emmm也没什么特别重要的信息，就看到了category参数进行了过滤判断。

输入参数必须包含woofers and meowers 以及index，否则无法包含文件。

 strpos函数是返回在输入字符串中第一次找到指定字符或字符串的位置，没找到就返回false。

接下来也可以去查看woofers and meowers两个文件去获取更多信息，但是两个php文件没啥用，没信息。

这时候只能靠直觉，全部信息只有这个过滤，那么绕过这个过滤就能找到flag。

flag一般都是藏在flag文件中，那么我们直接尝试读取flag文件，并且绕过index判断，这里有两个方法，一个是路径绕过，一个是伪协议过滤器绕过，把index放在这两个地方都可以：

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

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

 解码后成功获取flag

总结

一道基础的文件包含漏洞，去掉.php文件处需要心细一点分析报错信息，然后读取flag只能看直觉了，不过这个题的信息太少，也就只能读一下flag了