Servlet filter to integrate "X-Forwarded-For" and "X-Forwarded-Proto" HTTP headers.

Most of the design of this Servlet Filter is a port of mod_remoteip, this servlet filter replaces the apparent client remote IP address and hostname for the request with the IP address list presented by a proxy or a load balancer via a request headers (e.g. "X-Forwarded-For").

Another feature of this servlet filter is to replace the apparent scheme (http/https) and server port with the scheme presented by a proxy or a load balancer via a request header (e.g. "X-Forwarded-Proto").

This servlet filter proceeds as follows:

If the incoming request.getRemoteAddr() matches the servlet filter's list of internal or trusted proxies:

• Loop on the comma delimited list of IPs and hostnames passed by the preceding load balancer or proxy in the given request's Http header named $remoteIpHeader (default value x-forwarded-for). Values are processed in right-to-left order.
• For each ip/host of the list:
  • if it matches the internal proxies list, the ip/host is swallowed
  • if it matches the trusted proxies list, the ip/host is added to the created proxies header
  • otherwise, the ip/host is declared to be the remote ip and looping is stopped.
• If the request http header named $protocolHeader (default value X-Forwarded-Proto) consists only of forwards that match protocolHeaderHttpsValue configuration parameter (default https) then request.isSecure = true, request.scheme = https and request.serverPort = 443. Note that 443 can be overwritten with the $httpsServerPort configuration parameter.
• Mark the request with the attribute Globals#REQUEST_FORWARDED_ATTRIBUTE and value Boolean.TRUE to indicate that this request has been forwarded by one or more proxies.

Configuration parameters

XForwardedFilter property	Description	Equivalent mod_remoteip directive	Format	Default Value
remoteIpHeader	Name of the Http Header read by this servlet filter that holds the list of traversed IP addresses starting from the requesting client	RemoteIPHeader	Compliant http header name	x-forwarded-for
internalProxies	Regular expression that matches the IP addresses of internal proxies. If they appear in the remoteIpHeader value, they will be trusted and will not appear in the proxiesHeader value	RemoteIPInternalProxy	Regular expression (in the syntax supported by java.util.regex)	10\.\d{1,3}\.\d{1,3}\.\d{1,3}|192\.168\.\d{1,3}\.\d{1,3}| 169\.254\.\d{1,3}\.\d{1,3}|127\.\d{1,3}\.\d{1,3}\.\d{1,3}| 100\.6[4-9]{1}\.\d{1,3}\.\d{1,3}|100\.[7-9]{1}\d{1}\.\d{1,3}\.\d{1,3}| 100\.1[0-1]{1}\d{1}\.\d{1,3}\.\d{1,3}|100\.12[0-7]{1}\.\d{1,3}\.\d{1,3}| 172\.1[6-9]{1}\.\d{1,3}\.\d{1,3}|172\.2[0-9]{1}\.\d{1,3}\.\d{1,3}| 172\.3[0-1]{1}\.\d{1,3}\.\d{1,3}| 0:0:0:0:0:0:0:1|::1 By default, 10/8, 192.168/16, 169.254/16, 127/8, 100.64/10, 172.16/12, and 0:0:0:0:0:0:0:1 are allowed.
proxiesHeader	Name of the http header created by this servlet filter to hold the list of proxies that have been processed in the incoming remoteIpHeader	RemoteIPProxiesHeader	Compliant http header name	x-forwarded-by
trustedProxies	Regular expression that matches the IP addresses of trusted proxies. If they appear in the remoteIpHeader value, they will be trusted and will appear in the proxiesHeader value	RemoteIPTrustedProxy	Regular expression (in the syntax supported by java.util.regex)
protocolHeader	Name of the http header read by this servlet filter that holds the flag that this request	N/A	Compliant http header name like X-Forwarded-Proto, X-Forwarded-Ssl or Front-End-Https	X-Forwarded-Proto
protocolHeaderHttpsValue	Value of the protocolHeader to indicate that it is an Https request	N/A	String like https or ON	https
httpServerPort	Value returned by ServletRequest#getServerPort() when the protocolHeader indicates http protocol	N/A	integer	80
httpsServerPort	Value returned by ServletRequest#getServerPort() when the protocolHeader indicates https protocol	N/A	integer	443
enableLookups	Should a DNS lookup be performed to provide a host name when calling ServletRequest#getRemoteHost()	N/A	boolean	false

Regular expression vs. IP address blocks: mod_remoteip allows to use address blocks (e.g. 192.168/16) to configure RemoteIPInternalProxy and RemoteIPTrustedProxy ; as the JVM doesn't have a library similar to apr_ipsubnet_test, we rely on regular expressions.

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Sample with internal proxies

XForwardedFilter configuration:

<filter> <filter-name>RemoteIpFilter</filter-name> <filter-class>org.apache.catalina.filters.RemoteIpFilter</filter-class> <init-param> <param-name>internalProxies</param-name> <param-value>192\.168\.0\.10|192\.168\.0\.11</param-value> </init-param> <init-param> <param-name>remoteIpHeader</param-name> <param-value>x-forwarded-for</param-value> </init-param> <init-param> <param-name>remoteIpProxiesHeader</param-name> <param-value>x-forwarded-by</param-value> </init-param> <init-param> <param-name>protocolHeader</param-name> <param-value>x-forwarded-proto</param-value> </init-param> </filter> <filter-mapping> <filter-name>RemoteIpFilter</filter-name> <url-pattern>/*</url-pattern> <dispatcher>REQUEST</dispatcher> </filter-mapping>

Request Values

property	Value Before RemoteIpFilter	Value After RemoteIpFilter
request.remoteAddr	192.168.0.10	140.211.11.130
request.header['x-forwarded-for']	140.211.11.130, 192.168.0.10	null
request.header['x-forwarded-by']	null	null
request.header['x-forwarded-proto']	https	https
request.scheme	http	https
request.secure	false	true
request.serverPort	80	443

Note : x-forwarded-by header is null because only internal proxies as been traversed by the request. x-forwarded-by is null because all the proxies are trusted or internal.

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Sample with trusted proxies

RemoteIpFilter configuration:

<filter> <filter-name>RemoteIpFilter</filter-name> <filter-class>org.apache.catalina.filters.RemoteIpFilter</filter-class> <init-param> <param-name>internalProxies</param-name> <param-value>192\.168\.0\.10|192\.168\.0\.11</param-value> </init-param> <init-param> <param-name>remoteIpHeader</param-name> <param-value>x-forwarded-for</param-value> </init-param> <init-param> <param-name>remoteIpProxiesHeader</param-name> <param-value>x-forwarded-by</param-value> </init-param> <init-param> <param-name>trustedProxies</param-name> <param-value>proxy1|proxy2</param-value> </init-param> </filter> <filter-mapping> <filter-name>RemoteIpFilter</filter-name> <url-pattern>/*</url-pattern> <dispatcher>REQUEST</dispatcher> </filter-mapping>

Request Values

property	Value Before RemoteIpFilter	Value After RemoteIpFilter
request.remoteAddr	192.168.0.10	140.211.11.130
request.header['x-forwarded-for']	140.211.11.130, proxy1, proxy2	null
request.header['x-forwarded-by']	null	proxy1, proxy2

Note : proxy1 and proxy2 are both trusted proxies that come in x-forwarded-for header, they both are migrated in x-forwarded-by header. x-forwarded-by is null because all the proxies are trusted or internal.

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Sample with internal and trusted proxies

RemoteIpFilter configuration:

<filter> <filter-name>RemoteIpFilter</filter-name> <filter-class>org.apache.catalina.filters.RemoteIpFilter</filter-class> <init-param> <param-name>internalProxies</param-name> <param-value>192\.168\.0\.10|192\.168\.0\.11</param-value> </init-param> <init-param> <param-name>remoteIpHeader</param-name> <param-value>x-forwarded-for</param-value> </init-param> <init-param> <param-name>remoteIpProxiesHeader</param-name> <param-value>x-forwarded-by</param-value> </init-param> <init-param> <param-name>trustedProxies</param-name> <param-value>proxy1|proxy2</param-value> </init-param> </filter> <filter-mapping> <filter-name>RemoteIpFilter</filter-name> <url-pattern>/*</url-pattern> <dispatcher>REQUEST</dispatcher> </filter-mapping>

Request Values

property	Value Before RemoteIpFilter	Value After RemoteIpFilter
request.remoteAddr	192.168.0.10	140.211.11.130
request.header['x-forwarded-for']	140.211.11.130, proxy1, proxy2, 192.168.0.10	null
request.header['x-forwarded-by']	null	proxy1, proxy2

Note : proxy1 and proxy2 are both trusted proxies that come in x-forwarded-for header, they both are migrated in x-forwarded-by header. As 192.168.0.10 is an internal proxy, it does not appear in x-forwarded-by. x-forwarded-by is null because all the proxies are trusted or internal.

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Sample with an untrusted proxy

RemoteIpFilter configuration:

<filter> <filter-name>RemoteIpFilter</filter-name> <filter-class>org.apache.catalina.filters.RemoteIpFilter</filter-class> <init-param> <param-name>internalProxies</param-name> <param-value>192\.168\.0\.10|192\.168\.0\.11</param-value> </init-param> <init-param> <param-name>remoteIpHeader</param-name> <param-value>x-forwarded-for</param-value> </init-param> <init-param> <param-name>remoteIpProxiesHeader</param-name> <param-value>x-forwarded-by</param-value> </init-param> <init-param> <param-name>trustedProxies</param-name> <param-value>proxy1|proxy2</param-value> </init-param> </filter> <filter-mapping> <filter-name>RemoteIpFilter</filter-name> <url-pattern>/*</url-pattern> <dispatcher>REQUEST</dispatcher> </filter-mapping>

Request Values

property	Value Before RemoteIpFilter	Value After RemoteIpFilter
request.remoteAddr	192.168.0.10	untrusted-proxy
request.header['x-forwarded-for']	140.211.11.130, untrusted-proxy, proxy1	140.211.11.130
request.header['x-forwarded-by']	null	proxy1

Note : x-forwarded-by holds the trusted proxy proxy1. x-forwarded-by holds 140.211.11.130 because untrusted-proxy is not trusted and thus, we cannot trust that untrusted-proxy is the actual remote ip. request.remoteAddr is untrusted-proxy that is an IP verified by proxy1.

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