ipfilter

ipfilter

This is middleware for the Caddy web server that implements black and whitelisting based on IP addresses (or CIDR ranges) or country of origin using a MaxMind database.

Syntax

ipfilter <basepath> {
    rule       <block | allow>
    ip         <addresses or CIDR ranges to block>
    prefix_dir <IP addr directory prefix>
    database   </path/to/GeoLite2-Country.mmdb>
    country    <ISO two letter country codes>
    blockpage  <blockpage.html>
    strict
}

You can specify zero or more ipfilter blocks. Each ipfilter block has to specify at least one ip, prefix_dir or country directive. If no ipfilter blocks are defined this middleware will allow every request.

• basepath: A sequence of URI path prefixes to match for the filter to be active. You have to specify at least one path prefix. Use / to match every request. If the request doesn't match one of these prefixes the filter is ignored for purposes of determining if the request is blocked or allowed.

• rule: Should the filter block (blacklist) or allow (whitelist) the addresses. This directive is mandatory. It is an error to use it more than once per ipfilter block. The rule in effect for the last ipfilter block to match a request determines if it is blocked or allowed.

  Note that if you only have ipfilter blocks that specify rule allow then any request which doesn't match those filters will be implicitly blocked.

• ip: A sequence of IP adddresses or CIDR ranges to match. For example, ip 1.2.3.4 192.168.0.0/24 This is optional. It can be used more than once in each ipfilter block rather than enumerating all IPs after a single ip directive.

• prefix_dir: Specifies a directory in which to search for file names matching the IP address of the request. This is optional. It is an error to use this more than once per ipfilter block.

  You can specify a relative pathname to place it relative to the Caddy server CWD (which should be the content root dir). When putting the blacklisted directory in the web server document tree you should also add an internal directive to ensure those files are not visible via HTTP GET requests. For example, internal /blacklist/. You can also specify an absolute pathname to locate the blacklist directory outside the document tree. And the path can include environment vars. For example, prefix_dir {$HOME}/etc/www/blacklist.

  You can create the file in the root of the blacklist directory. This is known as using a "flat" namespace. For example, blacklist/127.0.0.1 or blacklist/2601:647:4601:fa93:1865:4b6c:d055:3f3. However, putting thousands of files in a single directory may cause poor performance of the lookup function. So you can also, and should, use a "sharded" namespace. This involves creating the file in a subdirectory based on the first two components of the address. For example, blacklist/127/0/127.0.0.1 or blacklist/2601/647/2601:647:4601:fa93:1865:4b6c:d055:3f3.

  Note that you can also whitelist IP addresses using this mechanism by specifying rule allow. This may be useful when it follows a more general blocking rule (e.g., by country) and you want to selectively allow some addresses through but don't want to hardcode the addresses in the Caddy config file.

  This mechanism is most useful when coupled with automated monitoring of your web server activity to detect signals that your server is under attack from malware. All your monitoring software has to do is create a file in the blacklist directory.

  At this time the content of the file is ignored. In the future the contents will probably be read and exposed as a placeholder variable for use in conjuction with a template to be filled in via the markdown directive. So you should consider putting some explanatory text in the file explaining why the address was blocked.

• database: Specifies the path to a MaxMind database. This is required if using the country directive; otherwise it should be omitted.

• country: A whitespace separated sequence of ISO two letter country codes to filter. This is optional but if used also requires a database directive. Note that if a country could not be found for the address it will be the empty string. This can be specified more than once per block rather than enumerating all countries on a single line.

• blockpage: Names the file to be returned if the ipfilter matches. Note that a http.StatusOK (200) status is returned if the page is successfully returned to the client. This is optional. If not specified then a http.StatusForbidden (403) status is returned.

• strict: Use this to disallow use of the address in the X-Forwarded-For request header if any. This is optional and defaults to false. If true or there is no X-Forwarded-For header use the address from the request remote address.

Caddyfile examples

Filter clients based on a given IP or range of IPs

ipfilter / {
	rule block
	ip 70.1.128.0/19 2001:db8::/122 9.12.20.16
}

caddy will block any clients with IPs that fall into one of these two ranges 70.1.128.0/19 and 2001:db8::/122 , or a client that has an IP of 9.12.20.16 explicitly.

ipfilter / {
	rule allow
	blockpage default.html
	ip 55.3.4.20 2e80::20:f8ff:fe31:77cf
}

caddy will serve only these 2 IPs, eveyone else will get default.html

ipfilter / {
	rule block
	prefix_dir blacklisted
}

caddy will block any client IP that appears as a file name in the blacklisted directory.

Filter clients based on their Country ISO Code

filtering with country codes requires a local copy of the Geo database, can be downloaded for free from MaxMind

ipfilter / {
	rule allow
	database /data/GeoLite.mmdb
	country US JP
}

with that in your Caddyfile caddy will only serve users from the United States or Japan

ipfilter /notglobal /secret {
	rule block
	database /data/GeoLite.mmdb
	blockpage default.html
	country US JP
}

having that in your Caddyfile caddy will ignore any requests from United States or Japan to /notglobal or /secret and it will show default.html instead, blockpage is optional.

Using mutiple ipfilter blocks

The ipfilter blocks are evaluated for each HTTP request in the order they appear. The last rule which matches a request is used to decide if the request is allowed. So in general you will want more general rules (e.g., blacklist an entire country) to appear before more specific rules (e.g., to whitelist specific address ranges).

ipfilter / {
	rule allow
	ip 32.55.3.10
}

ipfilter /webhook {
	rule allow
	ip 192.168.1.0/24
}

You can use as many ipfilter blocks as you please, the above says: block everyone but 32.55.3.10, Unless it falls in 192.168.1.0/24 and requesting a path in /webhook. Note that this is slightly subtle. Any request doesn't match any of those filters is implicitly blocked. In other words, there is no need to explicitly block every address followed by "allow" filters like those above.

Backward compatibility

ipfilter supports CIDR notation. This is the recommended way of specifiying ranges. The old formats of ranging over IPs will get converted to CIDR via range2CIDRs for the purpose of backward compatibility.