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# frozen_string_literal: true
require "action_dispatch/http/request"
module ActionDispatch
# This middleware guards from DNS rebinding attacks by explicitly permitting
# the hosts a request can be sent to.
#
# When a request comes to an unauthorized host, the +response_app+
# application will be executed and rendered. If no +response_app+ is given, a
# default one will run, which responds with +403 Forbidden+.
class HostAuthorization
class Permissions # :nodoc:
def initialize(hosts)
@hosts = sanitize_hosts(hosts)
end
def empty?
@hosts.empty?
end
def allows?(host)
@hosts.any? do |allowed|
allowed === host
rescue
# IPAddr#=== raises an error if you give it a hostname instead of
# IP. Treat similar errors as blocked access.
false
end
end
private
def sanitize_hosts(hosts)
Array(hosts).map do |host|
case host
when Regexp then sanitize_regexp(host)
when String then sanitize_string(host)
else host
end
end
end
def sanitize_regexp(host)
/\A#{host}\z/
end
def sanitize_string(host)
if host.start_with?(".")
/\A(.+\.)?#{Regexp.escape(host[1..-1])}\z/
else
host
end
end
end
DEFAULT_RESPONSE_APP = -> env do
request = Request.new(env)
format = request.xhr? ? "text/plain" : "text/html"
template = DebugView.new(host: request.host)
body = template.render(template: "rescues/blocked_host", layout: "rescues/layout")
[403, {
"Content-Type" => "#{format}; charset=#{Response.default_charset}",
"Content-Length" => body.bytesize.to_s,
}, [body]]
end
def initialize(app, hosts, response_app = nil)
@app = app
@permissions = Permissions.new(hosts)
@response_app = response_app || DEFAULT_RESPONSE_APP
end
def call(env)
return @app.call(env) if @permissions.empty?
request = Request.new(env)
if authorized?(request)
mark_as_authorized(request)
@app.call(env)
else
@response_app.call(env)
end
end
private
def authorized?(request)
origin_host = request.get_header("HTTP_HOST").to_s.sub(/:\d+\z/, "")
forwarded_host = request.x_forwarded_host.to_s.split(/,\s?/).last.to_s.sub(/:\d+\z/, "")
@permissions.allows?(origin_host) &&
(forwarded_host.blank? || @permissions.allows?(forwarded_host))
end
def mark_as_authorized(request)
request.set_header("action_dispatch.authorized_host", request.host)
end
end
end
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