require "ipaddr" module ActionDispatch # This middleware calculates the IP address of the remote client that is # making the request. It does this by checking various headers that could # contain the address, and then picking the last-set address that is not # on the list of trusted IPs. This follows the precedent set by e.g. # {the Tomcat server}[https://issues.apache.org/bugzilla/show_bug.cgi?id=50453], # with {reasoning explained at length}[http://blog.gingerlime.com/2012/rails-ip-spoofing-vulnerabilities-and-protection] # by @gingerlime. A more detailed explanation of the algorithm is given # at GetIp#calculate_ip. # # Some Rack servers concatenate repeated headers, like {HTTP RFC 2616}[http://www.w3.org/Protocols/rfc2616/rfc2616-sec4.html#sec4.2] # requires. Some Rack servers simply drop preceding headers, and only report # the value that was {given in the last header}[http://andre.arko.net/2011/12/26/repeated-headers-and-ruby-web-servers]. # If you are behind multiple proxy servers (like NGINX to HAProxy to Unicorn) # then you should test your Rack server to make sure your data is good. # # IF YOU DON'T USE A PROXY, THIS MAKES YOU VULNERABLE TO IP SPOOFING. # This middleware assumes that there is at least one proxy sitting around # and setting headers with the client's remote IP address. If you don't use # a proxy, because you are hosted on e.g. Heroku without SSL, any client can # claim to have any IP address by setting the X-Forwarded-For header. If you # care about that, then you need to explicitly drop or ignore those headers # sometime before this middleware runs. class RemoteIp class IpSpoofAttackError < StandardError; end # The default trusted IPs list simply includes IP addresses that are # guaranteed by the IP specification to be private addresses. Those will # not be the ultimate client IP in production, and so are discarded. See # http://en.wikipedia.org/wiki/Private_network for details. TRUSTED_PROXIES = [ "127.0.0.1", # localhost IPv4 "::1", # localhost IPv6 "fc00::/7", # private IPv6 range fc00::/7 "10.0.0.0/8", # private IPv4 range 10.x.x.x "172.16.0.0/12", # private IPv4 range 172.16.0.0 .. 172.31.255.255 "192.168.0.0/16", # private IPv4 range 192.168.x.x ].map { |proxy| IPAddr.new(proxy) } attr_reader :check_ip, :proxies # Create a new +RemoteIp+ middleware instance. # # The +ip_spoofing_check+ option is on by default. When on, an exception # is raised if it looks like the client is trying to lie about its own IP # address. It makes sense to turn off this check on sites aimed at non-IP # clients (like WAP devices), or behind proxies that set headers in an # incorrect or confusing way (like AWS ELB). # # The +custom_proxies+ argument can take an Array of string, IPAddr, or # Regexp objects which will be used instead of +TRUSTED_PROXIES+. If a # single string, IPAddr, or Regexp object is provided, it will be used in # addition to +TRUSTED_PROXIES+. Any proxy setup will put the value you # want in the middle (or at the beginning) of the X-Forwarded-For list, # with your proxy servers after it. If your proxies aren't removed, pass # them in via the +custom_proxies+ parameter. That way, the middleware will # ignore those IP addresses, and return the one that you want. def initialize(app, ip_spoofing_check = true, custom_proxies = nil) @app = app @check_ip = ip_spoofing_check @proxies = if custom_proxies.blank? TRUSTED_PROXIES elsif custom_proxies.respond_to?(:any?) custom_proxies else Array(custom_proxies) + TRUSTED_PROXIES end end # Since the IP address may not be needed, we store the object here # without calculating the IP to keep from slowing down the majority of # requests. For those requests that do need to know the IP, the # GetIp#calculate_ip method will calculate the memoized client IP address. def call(env) req = ActionDispatch::Request.new env req.remote_ip = GetIp.new(req, check_ip, proxies) @app.call(req.env) end # The GetIp class exists as a way to defer processing of the request data # into an actual IP address. If the ActionDispatch::Request#remote_ip method # is called, this class will calculate the value and then memoize it. class GetIp def initialize(req, check_ip, proxies) @req = req @check_ip = check_ip @proxies = proxies end # Sort through the various IP address headers, looking for the IP most # likely to be the address of the actual remote client making this # request. # # REMOTE_ADDR will be correct if the request is made directly against the # Ruby process, on e.g. Heroku. When the request is proxied by another # server like HAProxy or NGINX, the IP address that made the original # request will be put in an X-Forwarded-For header. If there are multiple # proxies, that header may contain a list of IPs. Other proxy services # set the Client-Ip header instead, so we check that too. # # As discussed in {this post about Rails IP Spoofing}[http://blog.gingerlime.com/2012/rails-ip-spoofing-vulnerabilities-and-protection/], # while the first IP in the list is likely to be the "originating" IP, # it could also have been set by the client maliciously. # # In order to find the first address that is (probably) accurate, we # take the list of IPs, remove known and trusted proxies, and then take # the last address left, which was presumably set by one of those proxies. def calculate_ip # Set by the Rack web server, this is a single value. remote_addr = ips_from(@req.remote_addr).last # Could be a CSV list and/or repeated headers that were concatenated. client_ips = ips_from(@req.client_ip).reverse forwarded_ips = ips_from(@req.x_forwarded_for).reverse # +Client-Ip+ and +X-Forwarded-For+ should not, generally, both be set. # If they are both set, it means that either: # # 1) This request passed through two proxies with incompatible IP header # conventions. # 2) The client passed one of +Client-Ip+ or +X-Forwarded-For+ # (whichever the proxy servers weren't using) themselves. # # Either way, there is no way for us to determine which header is the # right one after the fact. Since we have no idea, if we are concerned # about IP spoofing we need to give up and explode. (If you're not # concerned about IP spoofing you can turn the +ip_spoofing_check+ # option off.) should_check_ip = @check_ip && client_ips.last && forwarded_ips.last if should_check_ip && !forwarded_ips.include?(client_ips.last) # We don't know which came from the proxy, and which from the user raise IpSpoofAttackError, "IP spoofing attack?! " \ "HTTP_CLIENT_IP=#{@req.client_ip.inspect} " \ "HTTP_X_FORWARDED_FOR=#{@req.x_forwarded_for.inspect}" end # We assume these things about the IP headers: # # - X-Forwarded-For will be a list of IPs, one per proxy, or blank # - Client-Ip is propagated from the outermost proxy, or is blank # - REMOTE_ADDR will be the IP that made the request to Rack ips = [forwarded_ips, client_ips, remote_addr].flatten.compact # If every single IP option is in the trusted list, just return REMOTE_ADDR filter_proxies(ips).first || remote_addr end # Memoizes the value returned by #calculate_ip and returns it for # ActionDispatch::Request to use. def to_s @ip ||= calculate_ip end private def ips_from(header) # :doc: return [] unless header # Split the comma-separated list into an array of strings ips = header.strip.split(/[,\s]+/) ips.select do |ip| begin # Only return IPs that are valid according to the IPAddr#new method range = IPAddr.new(ip).to_range # we want to make sure nobody is sneaking a netmask in range.begin == range.end rescue ArgumentError nil end end end def filter_proxies(ips) # :doc: ips.reject do |ip| @proxies.any? { |proxy| proxy === ip } end end end end end