How to disable Django’s invalid HTTP_HOST error?

You shouldn’t be ignoring this error. Instead you should be denying the request before it reaches your Django backend. To deny requests with no HOST set you can use

SetEnvIfNoCase Host .+ VALID_HOST
Order Deny,Allow
Deny from All
Allow from env=VALID_HOST

or force the match to a particular domain (example.com)

SetEnvIfNoCase Host example\.com VALID_HOST
Order Deny,Allow
Deny from All
Allow from env=VALID_HOST