middleman/middleman-templates/lib/middleman-templates/html5/source/crossdomain.xml

<?xml version="1.0"?>
<!DOCTYPE cross-domain-policy SYSTEM "http://www.adobe.com/xml/dtds/cross-domain-policy.dtd">
<cross-domain-policy>
    <!-- Read this: www.adobe.com/devnet/articles/crossdomain_policy_file_spec.html -->

    <!-- Most restrictive policy: -->
    <site-control permitted-cross-domain-policies="none"/>

    <!-- Least restrictive policy: -->
    <!--
    <site-control permitted-cross-domain-policies="all"/>
    <allow-access-from domain="*" to-ports="*" secure="false"/>
    <allow-http-request-headers-from domain="*" headers="*" secure="false"/>
    -->
</cross-domain-policy>