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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}[],
# with {reasoning explained at length}[]
# 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}[]
# requires. Some Rack servers simply drop preceding headers, and only report
# the value that was {given in the last header}[].
# 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.
# 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
# for details.
^127\.0\.0\.1$ | # localhost IPv4
^::1$ | # localhost IPv6
^fc00: | # private IPv6 range fc00
^10\. | # private IPv4 range 10.x.x.x
^172\.(1[6-9]|2[0-9]|3[0-1])\.| # private IPv4 range ..
^192\.168\. # private IPv4 range 192.168.x.x
attr_reader :check_ip, :proxies
# Create a new +RemoteIp+ middleware instance.
# The +check_ip_spoofing+ 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 a regex, which will be used
# instead of +TRUSTED_PROXIES+, or a string, which 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, check_ip_spoofing = true, custom_proxies = nil)
@app = app
@check_ip = check_ip_spoofing
@proxies = case custom_proxies
when Regexp
when nil
Regexp.union(TRUSTED_PROXIES, custom_proxies)
# 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)
env["action_dispatch.remote_ip"] =, self)
# 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
# This constant contains a regular expression that validates every known
# form of IP v4 and v6 address, with or without abbreviations, adapted
# from {this gist}[].
VALID_IP = %r{
(^(25[0-5]|2[0-4][0-9]|1[0-9][0-9]|[0-9]{1,2})(\.(25[0-5]|2[0-4][0-9]|1[0-9][0-9]|[0-9]{1,2})){3}$) | # ip v4
(([0-9A-Fa-f]{1,4}:){7}[0-9A-Fa-f]{1,4}) | # ip v6 not abbreviated
(([0-9A-Fa-f]{1,4}:){6}:[0-9A-Fa-f]{1,4}) | # ip v6 with double colon in the end
(([0-9A-Fa-f]{1,4}:){5}:([0-9A-Fa-f]{1,4}:)?[0-9A-Fa-f]{1,4}) | # - ip addresses v6
(([0-9A-Fa-f]{1,4}:){4}:([0-9A-Fa-f]{1,4}:){0,2}[0-9A-Fa-f]{1,4}) | # - with
(([0-9A-Fa-f]{1,4}:){3}:([0-9A-Fa-f]{1,4}:){0,3}[0-9A-Fa-f]{1,4}) | # - double colon
(([0-9A-Fa-f]{1,4}:){2}:([0-9A-Fa-f]{1,4}:){0,4}[0-9A-Fa-f]{1,4}) | # - in the middle
(([0-9A-Fa-f]{1,4}:){6} ((\b((25[0-5])|(1\d{2})|(2[0-4]\d)|(\d{1,2}))\b)\.){3} (\b((25[0-5])|(1\d{2})|(2[0-4]\d)|(\d{1,2}))\b)) | # ip v6 with compatible to v4
(([0-9A-Fa-f]{1,4}:){1,5}:((\b((25[0-5])|(1\d{2})|(2[0-4]\d)|(\d{1,2}))\b)\.){3}(\b((25[0-5])|(1\d{2})|(2[0-4]\d)|(\d{1,2}))\b)) | # ip v6 with compatible to v4
(([0-9A-Fa-f]{1,4}:){1}:([0-9A-Fa-f]{1,4}:){0,4}((\b((25[0-5])|(1\d{2})|(2[0-4]\d)|(\d{1,2}))\b)\.){3}(\b((25[0-5])|(1\d{2})|(2[0-4]\d)|(\d{1,2}))\b)) | # ip v6 with compatible to v4
(([0-9A-Fa-f]{1,4}:){0,2}:([0-9A-Fa-f]{1,4}:){0,3}((\b((25[0-5])|(1\d{2})|(2[0-4]\d)|(\d{1,2}))\b)\.){3}(\b((25[0-5])|(1\d{2})|(2[0-4]\d)|(\d{1,2}))\b)) | # ip v6 with compatible to v4
(([0-9A-Fa-f]{1,4}:){0,3}:([0-9A-Fa-f]{1,4}:){0,2}((\b((25[0-5])|(1\d{2})|(2[0-4]\d)|(\d{1,2}))\b)\.){3}(\b((25[0-5])|(1\d{2})|(2[0-4]\d)|(\d{1,2}))\b)) | # ip v6 with compatible to v4
(([0-9A-Fa-f]{1,4}:){0,4}:([0-9A-Fa-f]{1,4}:){1}((\b((25[0-5])|(1\d{2})|(2[0-4]\d)|(\d{1,2}))\b)\.){3}(\b((25[0-5])|(1\d{2})|(2[0-4]\d)|(\d{1,2}))\b)) | # ip v6 with compatible to v4
(::([0-9A-Fa-f]{1,4}:){0,5}((\b((25[0-5])|(1\d{2})|(2[0-4]\d) |(\d{1,2}))\b)\.){3}(\b((25[0-5])|(1\d{2})|(2[0-4]\d)|(\d{1,2}))\b)) | # ip v6 with compatible to v4
([0-9A-Fa-f]{1,4}::([0-9A-Fa-f]{1,4}:){0,5}[0-9A-Fa-f]{1,4}) | # ip v6 with compatible to v4
(::([0-9A-Fa-f]{1,4}:){0,6}[0-9A-Fa-f]{1,4}) | # ip v6 with double colon at the beginning
(([0-9A-Fa-f]{1,4}:){1,7}:) # ip v6 without ending
def initialize(env, middleware)
@env = env
@check_ip = middleware.check_ip
@proxies = middleware.proxies
# 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}[],
# 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('REMOTE_ADDR').last
# Could be a CSV list and/or repeated headers that were concatenated.
client_ips = ips_from('HTTP_CLIENT_IP').reverse
forwarded_ips = ips_from('HTTP_X_FORWARDED_FOR').reverse
# +Client-Ip+ and +X-Forwarded-For+ should not, generally, both be set.
# If they are both set, it means that this request passed through two
# proxies with incompatible IP header conventions, and there is no way
# for us to determine which header is the right one after the fact.
# Since we have no idea, we give up and explode.
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=#{@env['HTTP_CLIENT_IP'].inspect} " +
# 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
# Memoizes the value returned by #calculate_ip and returns it for
# ActionDispatch::Request to use.
def to_s
@ip ||= calculate_ip
def ips_from(header)
# Split the comma-separated list into an array of strings
ips = @env[header] ? @env[header].strip.split(/[,\s]+/) : []
# Only return IPs that are valid according to the regex{ |ip| ip =~ VALID_IP }
def filter_proxies(ips)
ips.reject { |ip| ip =~ @proxies }
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