During the development of #33145, I have named a few concepts in the
code as `whitelisted`. We decided to stay away from the term and I
adjusted most of the code afterwards, but here are the cases I forgot to
change.
I also found a case in the API guide that we could have cleaned up as
well.
[ci skip]
The ActionDispatch::HostAuthorization is a new middleware that prevent
against DNS rebinding and other Host header attacks. By default it is
included only in the development environment with the following
configuration:
Rails.application.config.hosts = [
IPAddr.new("0.0.0.0/0"), # All IPv4 addresses.
IPAddr.new("::/0"), # All IPv6 addresses.
"localhost" # The localhost reserved domain.
]
In other environments, `Rails.application.config.hosts` is empty and no
Host header checks will be done. If you want to guard against header
attacks on production, you have to manually permit the allowed hosts
with:
Rails.application.config.hosts << "product.com"
The host of a request is checked against the hosts entries with the case
operator (#===), which lets hosts support entries of type RegExp,
Proc and IPAddr to name a few. Here is an example with a regexp.
# Allow requests from subdomains like `www.product.com` and
# `beta1.product.com`.
Rails.application.config.hosts << /.*\.product\.com/
A special case is supported that allows you to permit all sub-domains:
# Allow requests from subdomains like `www.product.com` and
# `beta1.product.com`.
Rails.application.config.hosts << ".product.com"
