1 files changed, 35 insertions, 0 deletions
diff --git a/app/controllers/concerns/internal_redirect.rb b/app/controllers/concerns/internal_redirect.rb
new file mode 100644
index 00000000000..7409b2e89a5
--- /dev/null
+++ b/app/controllers/concerns/internal_redirect.rb
@@ -0,0 +1,35 @@
+module InternalRedirect
+  extend ActiveSupport::Concern
+
+  def safe_redirect_path(path)
+    return unless path
+    # Verify that the string starts with a `/` but not a double `/`.
+    return unless path =~ %r{^/\w.*$}
+
+    uri = URI(path)
+    # Ignore anything path of the redirect except for the path, querystring and,
+    # fragment, forcing the redirect within the same host.
+    full_path_for_uri(uri)
+  rescue URI::InvalidURIError
+    nil
+  end
+
+  def safe_redirect_path_for_url(url)
+    return unless url
+
+    uri = URI(url)
+    safe_redirect_path(full_path_for_uri(uri)) if host_allowed?(uri)
+  rescue URI::InvalidURIError
+    nil
+  end
+
+  def host_allowed?(uri)
+    uri.host == request.host &&
+      uri.port == request.port
+  end
+
+  def full_path_for_uri(uri)
+    path_with_query = [uri.path, uri.query].compact.join('?')
+    [path_with_query, uri.fragment].compact.join("#")
+  end
+end