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<h1>
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247 CTF part 1
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<i class="fa fa-calendar padding-small"></i><time datetime="2019-11-09T10:01:00+01:00"> Sat 09 November 2019</time>
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<p>Recently I found new interesting wargame/ctf site <a href="https://247ctf.com/">247ctf</a>.
So let's try solving some of the challenges.</p>
<div class="toc">
<ul>
<li><a href="#the-more-the-merrier">The More The Merrier</a></li>
<li><a href="#the-secret-lock">The Secret Lock</a></li>
<li><a href="#text-editor-jail">Text Editor Jail</a></li>
<li><a href="#an-impossible-number">An Impossible Number</a></li>
<li><a href="#sensitive-server-memory">Sensitive Server Memory</a></li>
<li><a href="#the-flag-lottery">The Flag Lottery</a></li>
</ul>
</div>
<h2 id="the-more-the-merrier">The More The Merrier</h2>
<p>This is the first and easiest of reversing challenges offered.
Description:</p>
<blockquote>
<p>One byte is great. But what if you need more? Can you find the flag hidden in this binary?</p>
</blockquote>
<p>After not getting great results with Ghidra, I went along with IDA. Decompiling program in IDA we get:</p>
<div class="highlight"><pre><span></span><code><span class="kr">__int64</span><span class="w"> </span><span class="kr">__fastcall</span><span class="w"> </span><span class="n">main</span><span class="p">(</span><span class="kr">__int64</span><span class="w"> </span><span class="n">a1</span><span class="p">,</span><span class="w"> </span><span class="kt">char</span><span class="w"> </span><span class="o">**</span><span class="n">a2</span><span class="p">,</span><span class="w"> </span><span class="kt">char</span><span class="w"> </span><span class="o">**</span><span class="n">a3</span><span class="p">)</span>
<span class="p">{</span>
<span class="w"> </span><span class="n">puts</span><span class="p">(</span><span class="s">"Nothing to see here.."</span><span class="p">);</span>
<span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="mf">0L</span><span class="n">L</span><span class="p">;</span>
<span class="p">}</span>
</code></pre></div>
<p>So nothing much, after running <em>strings</em> on binary without success. I opened program in hex editor:</p>
<p><img alt="Rev flag" class="img-fluid centerimage" src="https://f3real.github.io/images/2019_11_9_247ctf_rev1.png"></p>
<p>and we get our flag. All in all, I feel it was more of steganography challenge then reversing but still a good introduction for beginners.</p>
<h2 id="the-secret-lock">The Secret Lock</h2>
<blockquote>
<p>Can you reverse the secret combination to open the lock and recover the flag?</p>
</blockquote>
<p>Now, this was an unexpected challenge! After extracting zip file we get html file .. It took me some time to find it since I was really expecting elf file.</p>
<p>Opening it in the browser we get a huge combination lock, 40 slots each having a range between 0 and 500. That's 40^500 combinations in total!</p>
<p>If we look at html source we can find huge if condition:</p>
<div class="highlight"><pre><span></span><code><span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="nb">Object</span><span class="p">.</span><span class="nx">keys</span><span class="p">(</span><span class="nx">flag</span><span class="p">).</span><span class="nx">length</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mf">40</span><span class="w"> </span><span class="o">&&</span><span class="w"> </span><span class="p">((</span><span class="nx">flag</span><span class="p">[</span><span class="mf">37</span><span class="p">]</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="nx">flag</span><span class="p">[</span><span class="mf">37</span><span class="p">])</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="nx">flag</span><span class="p">[</span><span class="mf">15</span><span class="p">]</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mf">0</span><span class="p">)</span><span class="w"> </span><span class="o">&&</span><span class="w"> </span><span class="p">((</span><span class="nx">flag</span><span class="p">[</span><span class="mf">3</span><span class="p">]</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="nx">flag</span><span class="p">[</span><span class="mf">31</span><span class="p">])</span><span class="w"> </span><span class="o">^</span><span class="w"> </span><span class="p">(</span><span class="nx">flag</span><span class="p">[</span><span class="mf">29</span><span class="p">]</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="nx">flag</span><span class="p">[</span><span class="mf">8</span><span class="p">])</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mf">234</span><span class="p">)</span><span class="w"> </span><span class="o">&&</span><span class="w"> </span><span class="p">((</span><span class="nx">flag</span><span class="p">[</span><span class="mf">32</span><span class="p">]</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="nx">flag</span><span class="p">[</span><span class="mf">12</span><span class="p">])</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="nx">flag</span><span class="p">[</span><span class="mf">9</span><span class="p">]</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="o">-</span><span class="mf">2332</span><span class="p">)</span><span class="w"> </span><span class="o">&&</span><span class="w"> </span><span class="p">((</span><span class="nx">flag</span><span class="p">[</span><span class="mf">24</span><span class="p">]</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="nx">flag</span><span class="p">[</span><span class="mf">27</span><span class="p">]</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="nx">flag</span><span class="p">[</span><span class="mf">13</span><span class="p">])</span><span class="w"> </span><span class="o">^</span><span class="w"> </span><span class="nx">flag</span><span class="p">[</span><span class="mf">6</span><span class="p">]</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mf">114</span><span class="p">)</span><span class="w"> </span><span class="o">&&</span><span class="w"> </span><span class="p">((</span><span class="nx">flag</span><span class="p">[</span><span class="mf">38</span><span class="p">]</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="nx">flag</span><span class="p">[</span><span class="mf">15</span><span class="p">])</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="nx">flag</span><span class="p">[</span><span class="mf">33</span><span class="p">]</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mf">800</span><span class="p">)</span><span class="w"> </span><span class="o">&&</span><span class="w"> </span><span class="p">((</span><span class="nx">flag</span><span class="p">[</span><span class="mf">34</span><span class="p">]</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="nx">flag</span><span class="p">[</span><span class="mf">21</span><span class="p">])</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="nx">flag</span><span class="p">[</span><span class="mf">26</span><span class="p">]</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mf">98</span><span class="p">)</span><span class="w"> </span><span class="o">&&</span><span class="w"> </span><span class="p">((</span><span class="nx">flag</span><span class="p">[</span><span class="mf">29</span><span class="p">]</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="nx">flag</span><span class="p">[</span><span class="mf">0</span><span class="p">])</span><span class="w"> </span><span class="o">^</span><span class="w"> </span><span class="p">(</span><span class="nx">flag</span><span class="p">[</span><span class="mf">8</span><span class="p">]</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="nx">flag</span><span class="p">[</span><span class="mf">38</span><span class="p">])</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mf">248</span><span class="p">)</span><span class="w"> </span><span class="o">&&</span><span class="w"> </span><span class="p">((</span><span class="nx">flag</span><span class="p">[</span><span class="mf">21</span><span class="p">]</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="nx">flag</span><span class="p">[</span><span class="mf">18</span><span class="p">])</span><span class="w"> </span><span class="o">^</span><span class="w"> </span><span class="p">(</span><span class="nx">flag</span><span class="p">[</span><span class="mf">7</span><span class="p">]</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="nx">flag</span><span class="p">[</span><span class="mf">15</span><span class="p">])</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mf">2694</span><span class="p">)</span><span class="w"> </span><span class="o">&&</span><span class="w"> </span><span class="p">((</span><span class="nx">flag</span><span class="p">[</span><span class="mf">28</span><span class="p">]</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="nx">flag</span><span class="p">[</span><span class="mf">23</span><span class="p">])</span><span class="w"> </span><span class="o">^</span><span class="w"> </span><span class="p">(</span><span class="nx">flag</span><span class="p">[</span><span class="mf">19</span><span class="p">]</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="nx">flag</span><span class="p">[</span><span class="mf">5</span><span class="p">])</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="o">-</span><span class="mf">9813</span><span class="p">)</span><span class="w"> </span><span class="o">&&</span><span class="w"> </span><span class="p">((</span><span class="nx">flag</span><span class="p">[</span><span class="mf">34</span><span class="p">]</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="nx">flag</span><span class="p">[</span><span class="mf">30</span><span class="p">])</span><span class="w"> </span><span class="o">^</span><span class="w"> </span><span class="p">(</span><span class="nx">flag</span><span class="p">[</span><span class="mf">37</span><span class="p">]</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="nx">flag</span><span class="p">[</span><span class="mf">6</span><span class="p">])</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mf">72</span><span class="p">)</span><span class="w"> </span><span class="o">&&</span><span class="w"> </span><span class="p">((</span><span class="nx">flag</span><span class="p">[</span><span class="mf">23</span><span class="p">]</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="nx">flag</span><span class="p">[</span><span class="mf">22</span><span class="p">])</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="nx">flag</span><span class="p">[</span><span class="mf">12</span><span class="p">]</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mf">4950</span><span class="p">)</span><span class="w"> </span><span class="o">&&</span><span class="w"> </span><span class="p">((</span><span class="nx">flag</span><span class="p">[</span><span class="mf">9</span><span class="p">]</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="nx">flag</span><span class="p">[</span><span class="mf">28</span><span class="p">])</span><span class="w"> </span><span class="o">^</span><span class="w"> </span><span class="p">(</span><span class="nx">flag</span><span class="p">[</span><span class="mf">20</span><span class="p">]</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="nx">flag</span><span class="p">[</span><span class="mf">11</span><span class="p">])</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mf">5143</span><span class="p">)</span><span class="w"> </span><span class="o">&&</span><span class="w"> </span><span class="p">((</span><span class="nx">flag</span><span class="p">[</span><span class="mf">2</span><span class="p">]</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="nx">flag</span><span class="p">[</span><span class="mf">22</span><span class="p">])</span><span class="w"> </span><span class="o">^</span><span class="w"> </span><span class="p">(</span><span class="nx">flag</span><span class="p">[</span><span class="mf">37</span><span class="p">]</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="nx">flag</span><span class="p">[</span><span class="mf">0</span><span class="p">])</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mf">2759</span><span class="p">)</span><span class="w"> </span><span class="o">&&</span><span class="w"> </span><span class="p">((</span><span class="nx">flag</span><span class="p">[</span><span class="mf">26</span><span class="p">]</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="nx">flag</span><span class="p">[</span><span class="mf">12</span><span class="p">])</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="nx">flag</span><span class="p">[</span><span class="mf">3</span><span class="p">]</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="o">-</span><span class="mf">3350</span><span class="p">)</span><span class="w"> </span><span class="o">&&</span><span class="w"> </span><span class="p">((</span><span class="nx">flag</span><span class="p">[</span><span class="mf">35</span><span class="p">]</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="nx">flag</span><span class="p">[</span><span class="mf">0</span><span class="p">])</span><span class="w"> </span><span class="o">^</span><span class="w"> </span><span class="p">(</span><span class="nx">flag</span><span class="p">[</span><span class="mf">23</span><span class="p">]</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="nx">flag</span><span class="p">[</span><span class="mf">21</span><span class="p">])</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mf">2698</span><span class="p">)</span><span class="w"> </span><span class="o">&&</span><span class="w"> </span><span class="p">((</span><span class="nx">flag</span><span class="p">[</span><span class="mf">20</span><span class="p">]</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="nx">flag</span><span class="p">[</span><span class="mf">31</span><span class="p">])</span><span class="w"> </span><span class="o">^</span><span class="w"> </span><span class="p">(</span><span class="nx">flag</span><span class="p">[</span><span class="mf">5</span><span class="p">]</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="nx">flag</span><span class="p">[</span><span class="mf">10</span><span class="p">])</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mf">22</span><span class="p">)</span><span class="w"> </span><span class="o">&&</span><span class="w"> </span><span class="p">((</span><span class="nx">flag</span><span class="p">[</span><span class="mf">31</span><span class="p">]</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="nx">flag</span><span class="p">[</span><span class="mf">19</span><span class="p">])</span><span class="w"> </span><span class="o">^</span><span class="w"> </span><span class="p">(</span><span class="nx">flag</span><span class="p">[</span><span class="mf">1</span><span class="p">]</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="nx">flag</span><span class="p">[</span><span class="mf">2</span><span class="p">])</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="o">-</span><span class="mf">2655</span><span class="p">)</span><span class="w"> </span><span class="o">&&</span><span class="w"> </span><span class="p">((</span><span class="nx">flag</span><span class="p">[</span><span class="mf">38</span><span class="p">]</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="nx">flag</span><span class="p">[</span><span class="mf">14</span><span class="p">])</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="nx">flag</span><span class="p">[</span><span class="mf">18</span><span class="p">]</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mf">55</span><span class="p">)</span><span class="w"> </span><span class="o">&&</span><span class="w"> </span><span class="p">((</span><span class="nx">flag</span><span class="p">[</span><span class="mf">29</span><span class="p">]</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="nx">flag</span><span class="p">[</span><span class="mf">19</span><span class="p">]</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="nx">flag</span><span class="p">[</span><span class="mf">10</span><span class="p">])</span><span class="w"> </span><span class="o">^</span><span class="w"> </span><span class="nx">flag</span><span class="p">[</span><span class="mf">2</span><span class="p">]</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mf">93</span><span class="p">)</span><span class="w"> </span><span class="o">&&</span><span class="w"> </span><span class="p">((</span><span class="nx">flag</span><span class="p">[</span><span class="mf">13</span><span class="p">]</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="nx">flag</span><span class="p">[</span><span class="mf">25</span><span class="p">]</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="nx">flag</span><span class="p">[</span><span class="mf">30</span><span class="p">])</span><span class="w"> </span><span class="o">^</span><span class="w"> </span><span class="nx">flag</span><span class="p">[</span><span class="mf">29</span><span class="p">]</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mf">13</span><span class="p">)</span><span class="w"> </span><span class="o">&&</span><span class="w"> </span><span class="p">((</span><span class="nx">flag</span><span class="p">[</span><span class="mf">35</span><span class="p">]</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="nx">flag</span><span class="p">[</span><span class="mf">33</span><span class="p">])</span><span class="w"> </span><span class="o">^</span><span class="w"> </span><span class="p">(</span><span class="nx">flag</span><span class="p">[</span><span class="mf">26</span><span class="p">]</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="nx">flag</span><span class="p">[</span><span class="mf">21</span><span class="p">])</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mf">249</span><span class="p">)</span><span class="w"> </span><span class="o">&&</span><span class="w"> </span><span class="p">((</span><span class="nx">flag</span><span class="p">[</span><span class="mf">17</span><span class="p">]</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="nx">flag</span><span class="p">[</span><span class="mf">24</span><span class="p">])</span><span class="w"> </span><span class="o">^</span><span class="w"> </span><span class="p">(</span><span class="nx">flag</span><span class="p">[</span><span class="mf">34</span><span class="p">]</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="nx">flag</span><span class="p">[</span><span class="mf">1</span><span class="p">])</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mf">253</span><span class="p">)</span><span class="w"> </span><span class="o">&&</span><span class="w"> </span><span class="p">.....</span>
</code></pre></div>
<p>Obviously, a job for SAT solver. I decided to go with Z3. After parsing if and splitting its conditions we can run our script and get our flag.</p>
<p>Python code <a href="https://github.com/F3real/ctf_solutions/blob/master/2019/247ctf/secret_sol.py">here</a>.</p>
<p>Interestingly biggest issue I had was with getting results from Z3 model so in the end I just manually modified printed output in notepad and gotten the flag.</p>
<h2 id="text-editor-jail">Text Editor Jail</h2>
<blockquote>
<p>We didn't have time to setup and test a proper jail, so this text editor will have to do for now. Can you break free?</p>
</blockquote>
<p>In vim/nvim we can run shell commands by using <code>:! <command></code> syntax.</p>
<p>Solution:</p>
<div class="highlight"><pre><span></span><code>:! ls
:! ./run_for_flag
</code></pre></div>
<h2 id="an-impossible-number">An Impossible Number</h2>
<blockquote>
<p>Can you think of a number which at the same time is one more than itself?</p>
</blockquote>
<p>Let's look at provided c source:</p>
<div class="highlight"><pre><span></span><code><span class="cp">#include</span><span class="w"> </span><span class="cpf"><stdio.h></span>
<span class="kt">int</span><span class="w"> </span><span class="nf">main</span><span class="p">()</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">impossible_number</span><span class="p">;</span>
<span class="w"> </span><span class="kt">FILE</span><span class="w"> </span><span class="o">*</span><span class="n">flag</span><span class="p">;</span>
<span class="w"> </span><span class="kt">char</span><span class="w"> </span><span class="n">c</span><span class="p">;</span>
<span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="n">scanf</span><span class="p">(</span><span class="s">"%d"</span><span class="p">,</span><span class="w"> </span><span class="o">&</span><span class="n">impossible_number</span><span class="p">))</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="n">impossible_number</span><span class="w"> </span><span class="o">></span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="o">&&</span><span class="w"> </span><span class="n">impossible_number</span><span class="w"> </span><span class="o">></span><span class="w"> </span><span class="p">(</span><span class="n">impossible_number</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mi">1</span><span class="p">))</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="n">flag</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">fopen</span><span class="p">(</span><span class="s">"flag.txt"</span><span class="p">,</span><span class="s">"r"</span><span class="p">);</span>
<span class="w"> </span><span class="k">while</span><span class="p">((</span><span class="n">c</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">getc</span><span class="p">(</span><span class="n">flag</span><span class="p">))</span><span class="w"> </span><span class="o">!=</span><span class="w"> </span><span class="n">EOF</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="n">printf</span><span class="p">(</span><span class="s">"%c"</span><span class="p">,</span><span class="n">c</span><span class="p">);</span>
<span class="w"> </span><span class="p">}</span>
<span class="w"> </span><span class="p">}</span>
<span class="w"> </span><span class="p">}</span>
<span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span>
<span class="p">}</span>
</code></pre></div>
<p>Max signed 32 int is 2 147 483 647. Adding 1 to it will turn it negative and we can pass our check.</p>
<div class="highlight"><pre><span></span><code>nc <url> <port>
2147483647
</code></pre></div>
<h2 id="sensitive-server-memory">Sensitive Server Memory</h2>
<blockquote>
<p>The webserver for this challenge is storing sensitive data in memory. Can you read it? Did anybody patch since 2014?</p>
</blockquote>
<p>After reading the description it is obviously a reference to one of the more famous vulnerabilities, heartbleed. Using available POC on a given server is enough to solve this challenge.</p>
<div class="highlight"><pre><span></span><code>python .\heartbleed.py <url_without_tcp://> -p <port>
</code></pre></div>
<h2 id="the-flag-lottery">The Flag Lottery</h2>
<blockquote>
<p>Can you guess the secret number to win the lottery? The prize is a flag!</p>
</blockquote>
<p>Challenge source:</p>
<div class="highlight"><pre><span></span><code><span class="kn">import</span> <span class="nn">SocketServer</span><span class="o">,</span> <span class="nn">threading</span><span class="o">,</span> <span class="nn">random</span><span class="o">,</span> <span class="nn">time</span>
<span class="k">class</span> <span class="nc">ThreadedLotteryServer</span><span class="p">(</span><span class="n">SocketServer</span><span class="o">.</span><span class="n">ThreadingMixIn</span><span class="p">,</span> <span class="n">SocketServer</span><span class="o">.</span><span class="n">TCPServer</span><span class="p">):</span>
<span class="k">pass</span>
<span class="k">class</span> <span class="nc">LotteryHandler</span><span class="p">(</span><span class="n">SocketServer</span><span class="o">.</span><span class="n">BaseRequestHandler</span><span class="p">):</span>
<span class="k">def</span> <span class="nf">handle</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
<span class="n">secret</span> <span class="o">=</span> <span class="n">random</span><span class="o">.</span><span class="n">Random</span><span class="p">()</span>
<span class="n">secret</span><span class="o">.</span><span class="n">seed</span><span class="p">(</span><span class="nb">int</span><span class="p">(</span><span class="n">time</span><span class="o">.</span><span class="n">time</span><span class="p">()))</span>
<span class="n">winning_choice</span> <span class="o">=</span> <span class="nb">str</span><span class="p">(</span><span class="n">secret</span><span class="o">.</span><span class="n">random</span><span class="p">())</span>
<span class="bp">self</span><span class="o">.</span><span class="n">request</span><span class="o">.</span><span class="n">sendall</span><span class="p">(</span><span class="s2">"Can you guess the number to win the flag lottery?</span><span class="se">\n</span><span class="s2">"</span><span class="p">)</span>
<span class="n">your_choice</span> <span class="o">=</span> <span class="bp">self</span><span class="o">.</span><span class="n">request</span><span class="o">.</span><span class="n">recv</span><span class="p">(</span><span class="mi">1024</span><span class="p">)</span><span class="o">.</span><span class="n">strip</span><span class="p">()</span>
<span class="k">if</span> <span class="n">winning_choice</span> <span class="o">==</span> <span class="n">your_choice</span><span class="p">:</span>
<span class="bp">self</span><span class="o">.</span><span class="n">request</span><span class="o">.</span><span class="n">sendall</span><span class="p">(</span><span class="s2">"Congratulations you won the lottery! Have a flag!</span><span class="se">\n</span><span class="s2">"</span><span class="p">)</span>
<span class="bp">self</span><span class="o">.</span><span class="n">request</span><span class="o">.</span><span class="n">sendall</span><span class="p">(</span><span class="s2">"</span><span class="si">%s</span><span class="se">\n</span><span class="s2">"</span> <span class="o">%</span> <span class="nb">open</span><span class="p">(</span><span class="s1">'flag.txt'</span><span class="p">)</span><span class="o">.</span><span class="n">readline</span><span class="p">()</span><span class="o">.</span><span class="n">rstrip</span><span class="p">())</span>
<span class="k">else</span><span class="p">:</span>
<span class="bp">self</span><span class="o">.</span><span class="n">request</span><span class="o">.</span><span class="n">sendall</span><span class="p">(</span><span class="s2">"Nope! The winning number was </span><span class="si">%s</span><span class="s2">, better luck next time!</span><span class="se">\n</span><span class="s2">"</span> <span class="o">%</span> <span class="n">winning_choice</span><span class="p">)</span>
<span class="k">return</span>
<span class="k">if</span> <span class="vm">__name__</span> <span class="o">==</span> <span class="s1">'__main__'</span><span class="p">:</span>
<span class="n">SocketServer</span><span class="o">.</span><span class="n">TCPServer</span><span class="o">.</span><span class="n">allow_reuse_address</span> <span class="o">=</span> <span class="kc">True</span>
<span class="n">server</span> <span class="o">=</span> <span class="n">ThreadedLotteryServer</span><span class="p">((</span><span class="s2">"0.0.0.0"</span><span class="p">,</span> <span class="mi">5000</span><span class="p">),</span> <span class="n">LotteryHandler</span><span class="p">)</span>
<span class="n">server_thread</span> <span class="o">=</span> <span class="n">threading</span><span class="o">.</span><span class="n">Thread</span><span class="p">(</span><span class="n">target</span><span class="o">=</span><span class="n">server</span><span class="o">.</span><span class="n">serve_forever</span><span class="p">)</span>
<span class="n">server_thread</span><span class="o">.</span><span class="n">daemon</span> <span class="o">=</span> <span class="kc">True</span>
<span class="n">server_thread</span><span class="o">.</span><span class="n">start</span><span class="p">()</span>
<span class="n">server</span><span class="o">.</span><span class="n">serve_forever</span><span class="p">()</span>
</code></pre></div>
<p>The problem lies in incorrectly initialized random. We can simply initialize it in the same way (with a small added time delay of 1 sec) and get the correct solution.</p>
<p>Note: The solution requires python 2. On python 3 precision of random differs a bit and won't produce the same results.</p>
<p>All provided challenges and solutions can be found on <a href="https://github.com/F3real/ctf_solutions/tree/master/2019/247ctf">github repo</a>.</p>
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elm.classList.toggle('collapsed');
document.getElementById(selector).classList.toggle('show');
}, false);
}
function showBigNav() {;
sidebarBig.style.display = 'block';
sidebarSmall.style.display = 'none';
}
function showSmallNav() {
sidebarBig.style.display = 'none';
sidebarSmall.style.display = 'block';
}
const mediaQuery = window.matchMedia('(min-width:768px)');
mediaQuery.onchange = e => {
if (wrapper.classList.contains('toggled')) {
wrapper.classList.remove('toggled');
} else {
if (e.matches) {
showBigNav();
} else {
showSmallNav();
}
}
}
function setNavbar() {
var condition = wrapper.classList.contains('toggled');
if (!mediaQuery.matches) {
condition = !condition;
}
if (condition) {
showSmallNav();
} else {
showBigNav();
}
}
function toggleMenu(){
wrapper.classList.toggle('toggled');
setNavbar();
}
window.onload = setNavbar;
</script>
<script data-goatcounter="https://f3real.goatcounter.com/count"
async src="//gc.zgo.at/count.js"></script>
</body>
</html>