You can prevent browsing to /blog
on non-www.mysite.com
sites using a UrlRewrite rule:
<rule name="RequestBlockingRule1" patternSyntax="Wildcard" stopProcessing="true">
<match url="*" />
<conditions logicalGrouping="MatchAll">
<add input="{URL}" pattern="/blog*" />
<add input="{HTTP_HOST}" pattern="www.mysite.com" negate="true" />
</conditions>
<action
type="CustomResponse" statusCode="403"
statusReason="Forbidden: Access is denied."
statusDescription="You do not have permission to view this directory or page." />
</rule>