When running on servers that are configured to accept a wildcard as a hostname (i.e. the server routes any request, regardless of the HOST header to an October CMS instance) the potential exists for Host Header Poisoning attacks to succeed. See the following resources for more information on Host Header Poisoning:
Check that the configuration setting cms.linkPolicy is set to force.
Alternative Workaround
Check to make sure that your web server does not accept any hostname when serving your web application.
Add an entry called testing.tld to your computer's host file and direct it to your server's IP address
Open the address testing.tld in your web browser
Make sure an October CMS website is not available at this address
If an October CMS website is returned, configure your webserver to only allow known hostnames. If you require assistance with this, please contact your server administrator.