Drupal Trusted Host Settings

As of January 2015, Drupal supports "trusted host patterns", where you can (and should) specify a set of regular expressions that the domains on incoming requests must match. Example configuration in settings.php would read:

$settings['trusted_host_patterns'] = array(
'^www\.example\.co.uk$',
'^example\.co.uk$',
);

See the above change record for more details. Note that, if you're doing local development, you might get (temporarily) locked out of your site by the above configuration on its own. You should add a trusted host pattern for '^localhost$' in this case.

See also: https://www.drupal.org/node/1992030