mod_extforward¶

• Table of contents
• mod_extforward
  • Description
  • Options
  • Samples
  • Using $HTTP["scheme"] rules
  • Security

Module: mod_extforward

Description¶

This module will extract the client's "real" IP from Forwarded or X-Forwarded-For header which is added by Squid or other proxies. It might be useful for servers behind reverse proxy servers.

Options¶

• extforward.headers
  Sets headers to search for finding the original addresses.

  Default: empty, results in searching for "X-Forwarded-For" and "Forwarded-For"

  Example (for use with a Zeus ZXTM loadbalancer):
  

  extforward.headers = ("X-Cluster-Client-Ip")

  Since lighttpd 1.4.46, mod_extforward supports "Forwarded" (RFC7239). Since the header is spoofable through proxies which do not understand "Forwarded", this is not enabled by default and must be configured e.g. with extforward.headers = ("Forwarded", "X-Forwarded-For")

• extforward.forwarder
  Sets trust level of proxy IP's.

  Default: empty

  Example of usage:
  

  extforward.forwarder = ("10.0.0.232" => "trust")  

  will translate ip addresses coming from 10.0.0.232 to real ip addresses extracted from X-Forwarded-For (or whatever is specified in extforward.headers) HTTP request header.

  CIDR masks (e.g. "10.0.0.0/8" => "trust") are supported (since 1.4.50), but only for trusted IPs (not "untrusted").

  Important note:

  The effect of this module is variable on $HTTP["remoteip"] directives and other module's remote ip dependent actions.
  Things done by modules before we change the remoteip or after we reset it will match on the proxy's IP.
  Things done in between these two moments will match on the real client's IP.
  The moment things are done by a module depends on in which hook it does things and within the same hook
  on whether they are before/after us in the module loading order
  (order in the server.modules directive in the config file).

Tested behaviours:

mod_access: Will match on the real client.

mod_accesslog: In order to see the "real" ip address in access log, you'll have to load mod_extforward after mod_accesslog, like this:

    server.modules  = (
       .....
       "mod_accesslog",
       "mod_extforward" 
    )

• extforward.params (since 1.4.46)
  When processing "Forwarded" request header, extforward.params sets which values to propagate. "for" and "proto" are always enabled (not configurable) to maintain the existing behavior in mod_extforward. See also Docs_ModProxy for proxy.forwarded.
  

      extforward.params = ( #"host" => 1,        # overwrite "Host" with Forwarded value
                            #"remote_user" => 1, # set REMOTE_USER with Forwarded value
      )
  

• extforward.hap-PROXY (since 1.4.46)
  Enable processing of HAProxy PROXY protocol v1 or v2 (http://www.haproxy.org/download/1.8/doc/proxy-protocol.txt)
  mod_extforward must be loaded after mod_openssl in server.modules for this to work. Also, note that when extforward.hap-PROXY = "enable", mod_extforward will process HAProxy PROXY protocol requests only for trusted proxies configured in extforward.forwarder. The client IP address presented to other modules such as mod_access and mod_accesslog will be the IP address provided by the HAProxy PROXY protocol.

• extforward.hap-PROXY-ssl-client-verify (since 1.4.46)
  Enable setting SSL_CLIENT_VERIFY from HAProxy PROXY protocol.

Samples¶

Trust proxy 2001:db8::232, 2001:db8::233, 10.0.0.232 and 10.0.0.233

  extforward.forwarder = (
     "2001:db8::232" => "trust",
     "2001:db8::233" => "trust" 
     "10.0.0.232" => "trust",
     "10.0.0.233" => "trust" 
  )

Trust all proxies (NOT RECOMMENDED!)

  extforward.forwarder = ( "all" => "trust")

Note that "all" has precedence over specific entries, so "all except" setups will not work.

Using $HTTP["scheme"] rules¶

If you are running lighttpd behind a reverse proxy (such as haproxy) to provide HTTPS termination, you may want to configure lighttpd rules which act on $HTTP["scheme"] == "https" etc
As of lighttpd 1.4.40, mod_extforward is able to detect the scheme from the front proxy, allowing you to use scheme based conditional rules in lighttpd.conf

In order to do this, extforward.headers (default X-Forwarded-For, Forwarded-For) must match a corresponding HTTP request header, as well as the proxy being "trusted" via extforward.forwarder

Security¶

In general, data from external sources should not be trusted. This includes HTTP request headers. In certain controlled environments, it may be desirable to extend limited trust to some of this information. mod_extforward trusts some information provided by proxies with IPs that mod_extforward has been configured to trust. These proxies must, in turn, be configured to always append information to the headers mod_extforward trusts, e.g. X-Forwarded-For.

There are many (non-standard) HTTP request header extensions and conventions proposed over the years in order to propagate IP and other information through proxies since that information might otherwise be unavailable to proxies further down the line. Depending on the specific configuration of an environment, and the specific security requirements of that environment, it may be desirable to have lighttpd forcefully remove one or more non-standard HTTP request headers, e.g. using mod_setenv setenv.set-request-header (since 1.4.46) and setting the values to blank "" to have them omitted. This may be useful if lighttpd mod_proxy is going to act as reverse proxy, or if it is undesirable in a specific environment to have CGI, FastCGI, SCGI, etc. see these request headers.

    setenv.set-request-header = ( #"Forwarded" => "",          # RFC7239; the only standard HTTP request header in this list
                                  #"X-Forwarded-For" => "",    # most common convention (non-standard HTTP request header)
                                  #"X-Forwarded-Proto" => "",  # (used by mod_extforward if extforward.headers uses X-Forwarded-For)
                                  #"X-Host" => "",             # set by lighttpd with Host
                                  #"X-Forwarded-Host" => "",   # most common convention to which to append Host (set in lighttpd 1.4.46)
                                  "X-Forwarded-Server" => "",  # fallback used by some frameworks if X-Forwarded-Host not present
                                  "X-Forwarded-By" => "",
                                  "X-Origin-IP" => "",
                                  "X-Original-To" => "",
                                  "Forwarded-For" => "",
                                  "Via" => "",
                                  #... (more; not an exhaustive list)
                                )