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<title>The "Quiz Your Friends" XSS Exploit | tait.tech</title>
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<h1>The "Quiz Your Friends" XSS Exploit</h1>
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<h4 class="post-date line-under"></h4>
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<div class="article">
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<h2 id="todo-write-intro">TODO write intro</h2>
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<h2 id="how-i-found-this-exploit">How I Found This Exploit</h2>
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<p>While filling in one of my friend’s surveys I thought it would be
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funny for them to know it is me without anyone else knowing.
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We were young and had <code class="highlighter-rouge">Inspect Element</code>ed a few things together,
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so it was a safe bet that an HTML joke would let them know.</p>
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<p>So I typed in my name like so:</p>
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<p><code class="highlighter-rouge">BOLD_STEVE.JPG</code></p>
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<p>Now in theory this should have shown in in the leaderboard as: “<b>Bold Steve</b>”
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However, to my horror and excitement, I saw this in the leaderboard:</p>
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<p><code class="highlighter-rouge">BOLD_STEVE_LEADERBOARD.JPG</code></p>
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<p>The text “Bold Steve” showed up <strong>in bold</strong> on the leaderboard.
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This told me all I needed to know. To add a <code class="highlighter-rouge"><script></code> tag was next.</p>
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<h4 id="hacking">Hacking:</h4>
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<p>So I went on my merry way thinking about ways to use malicious javascript.
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Then, I thought that might be mean, so I decided to warn users instead.
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I filled in the name with a script tag and a call to <code class="highlighter-rouge">alert()</code> to warn the user about this site.</p>
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<p><code class="highlighter-rouge">JAVASCRIPT_NAME.JPG</code></p>
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<p>I ran out of room before I could finish it. Hmmm.
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What if I do “Inspect Element” and manually override the max-length attribute?</p>
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<p>The unfortunate truth is: this worked as well!</p>
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<p>Not only could I manually set the max-length by changing it in the HTML,
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but there were no client-side OR server-side checks to make sure the name I was sending was less than or equal to 20 characters.</p>
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<p>If Javascript checked it, it would have stopped me (although maybe not a professional).
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If the server checked it, it could have stopped almost anyone.</p>
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<h5 id="server-side-validation">Server-Side Validation</h5>
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<p>As a side note, here is a great reason why you should do most of your validation on the server side.
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As a user, I can edit any of the HTML, CSS, or Javascript your server serves to me.</p>
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<p>Imagine trying to fit in a script tag doing anything useful with 20 characters?</p>
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<p><code class="highlighter-rouge"><script src="http:"></code></p>
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<p>There’s your 20 characters! No more! Good luck trying to do anything useful with this!</p>
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<p>The Quiz My Friends server has <em>no such checks in place</em>.
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Therefore, I can send an almost arbitrary load to them.
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Being able to send something potentially very large (more than a few megabytes) is a vulnerability of its own.
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Imagine being able to send entire executable progrmas as your “name” in one of these quizes?</p>
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<h2 id="executing-an-exploit">Executing An Exploit</h2>
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<p>Suppose we’re on a vulnerable site like <a href="https://www.quizyourfriends.com/">Quiz Your Friends</a>
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and you decide you want to hack your friend’s quiz!
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How can this be done?</p>
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<h4 id="creating-a-quiz">Creating A Quiz</h4>
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<p>Here is my quiz below:</p>
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<p><code class="highlighter-rouge">CREATING_QUIZ.IMG</code></p>
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<h4 id="setting-a-name-with-an-html-tag">Setting A Name With an HTML Tag</h4>
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<p>Just like the image above, about how I found out about this vulnerability: go ahead and use an HTML tag in your name to test this out.</p>
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<p><code class="highlighter-rouge">BOLD_ITALIC_STEVE.JPG</code></p>
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<footer>
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This page is mirrored on <a href="https://beta.tait.tech/2020-04-27-quiz-your-friends-xss.html">beta.tait.tech</a>.
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