[MRCTF2020]Ez_bypass

Posted 2021-05-14 H3h3QAQ

[MRCTF2020]Ez_bypass

打开后是一串php代码

I put something in F12 for you
include 'flag.php';
$flag='MRCTF{xxxxxxxxxxxxxxxxxxxxxxxxx}';
if(isset($_GET['gg'])&&isset($_GET['id'])) {
    $id=$_GET['id'];
    $gg=$_GET['gg'];
    if (md5($id) === md5($gg) && $id !== $gg) {
        echo 'You got the first step';
        if(isset($_POST['passwd'])) {
            $passwd=$_POST['passwd'];
            if (!is_numeric($passwd))
            {
                 if($passwd==1234567)
                 {
                     echo 'Good Job!';
                     highlight_file('flag.php');
                     die('By Retr_0');
                 }
                 else
                 {
                     echo "can you think twice??";
                 }
            }
            else{
                echo 'You can not get it !';
            }

        }
        else{
            die('only one way to get the flag');
        }
}
    else {
        echo "You are not a real hacker!";
    }
}
else{
    die('Please input first');
}
}Please input first

打开靶机是一串php代码

审计过后发现是md5绕过

if (md5($id) === md5($gg) && $id !== $gg)

在这说一下原理：

md5()函数无法操作数组，返回NULL，两个NULL相等

即可绕过这一关

构造payload：

http://5c026421-c5fb-49bb-ae03-a80c3bf2bd3b.node3.buuoj.cn/?id[]=1&gg[]=1

is_numeric()直接用1234567a 绕过即可

让后再用hackbar POST传值即可