From 76996bce1051f47acda2a0b77f882625050fde98 Mon Sep 17 00:00:00 2001
From: Alex Ghiculescu <alex@tanda.co>
Date: Wed, 28 Jul 2021 13:36:55 -0500
Subject: [PATCH] Add more detail about what hosts are allowed

Fixes https://github.com/rails/rails/issues/41545
---
 .../middleware/templates/rescues/blocked_host.html.erb          | 2 +-
 .../middleware/templates/rescues/blocked_host.text.erb          | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/actionpack/lib/action_dispatch/middleware/templates/rescues/blocked_host.html.erb b/actionpack/lib/action_dispatch/middleware/templates/rescues/blocked_host.html.erb
index f6637b70c8a6a..cbef57e15dd69 100644
--- a/actionpack/lib/action_dispatch/middleware/templates/rescues/blocked_host.html.erb
+++ b/actionpack/lib/action_dispatch/middleware/templates/rescues/blocked_host.html.erb
@@ -2,6 +2,6 @@
   <h1>Blocked host: <%= @host %></h1>
 </header>
 <main role="main" id="container">
-  <h2>To allow requests to <%= @host %>, add the following to your environment configuration:</h2>
+  <h2>To allow requests to <%= @host %> make sure it is a valid hostname (containing only numbers, letters, dashes and dots), then add the following to your environment configuration:</h2>
   <pre>config.hosts &lt;&lt; "<%= @host %>"</pre>
 </main>
diff --git a/actionpack/lib/action_dispatch/middleware/templates/rescues/blocked_host.text.erb b/actionpack/lib/action_dispatch/middleware/templates/rescues/blocked_host.text.erb
index a94dd982a7078..75483ac8c829c 100644
--- a/actionpack/lib/action_dispatch/middleware/templates/rescues/blocked_host.text.erb
+++ b/actionpack/lib/action_dispatch/middleware/templates/rescues/blocked_host.text.erb
@@ -1,5 +1,5 @@
 Blocked host: <%= @host %>
 
-To allow requests to <%= @host %>, add the following to your environment configuration:
+To allow requests to <%= @host %> make sure it is a valid hostname (containing only numbers, letters, dashes and dots), then add the following to your environment configuration:
 
   config.hosts << "<%= @host %>"