Anti-Abuse for servers at authentication time
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Build Status

The goal of 'wforce' is to detect brute forcing of passwords across many servers, services and instances. In order to support the real world, brute force detection policy can be tailored to deal with "bulk, but legitimate" users of your service, as well as botnet-wide slowscans of passwords.

The aim is to support the largest of installations, providing services to hundreds of millions of users. The current version of weakforced is not quite there yet, although it certainly scales to support up to ten million users, if not more. The limiting factor is number of logins per second at peak.

Wforce is a project by Dovecot, PowerDNS and Open-Xchange. For historical reasons, it lives in the PowerDNS github tree. If you have any questions, email

Here is how it works:

  • Report successful logins via JSON http-api
  • Report unsuccessful logins via JSON http-api
  • Query if a login should be allowed to proceed, should be delayed, or ignored via http-api
  • API for querying the status of logins, IP addresses etc.
  • Runtime console for server introspection

wforce is aimed to receive message from services like:

  • IMAP
  • POP3
  • Webmail logins
  • FTP logins
  • Authenticated SMTP
  • Self-service logins
  • Password recovery services

By gathering failed and successful login attempts from as many services as possible, brute forcing attacks as well as other suspicious behaviour can be detected and prevented more effectively.



From GitHub:

$ git clone
$ cd weakforced
$ autoreconf -i
$ ./configure
$ make

This requires recent versions of libtool, automake and autoconf to be installed. Secondly, we require (versions tagged up to 1.0.0):

  • Recent g++ (5.0+)
  • Boost 1.40+
  • Lua 5.1+ development libraries (or LuaJIT if you configure --with-luajit)
  • Getdns development libraries (if you want to use the DNS lookup functionality)
  • libsodium
  • python + virtualenv for regression testing
  • libgeoip-dev for GeoIP support
  • libsystemd-dev for systemd support
  • pandoc for building the manpages

The most recent versions also require:

  • Protobuf compiler and protobuf development libraries
  • libcurl-dev (OpenSSL version)
  • libhiredis-dev
  • libssl-dev
  • python-bottle for regression testing of webhooks

To build on OS X, brew install readline gcc and use ./configure LDFLAGS=-L/usr/local/opt/readline/lib CPPFLAGS=-I/usr/local/opt/readline/include CC=gcc-5 CXX=g++-5 CPP=cpp-5

Add --with-luajit to the end of the configure line if you want to use LuaJIT.


There is a sensible, if very simple, default policy in wforce.conf (running without this means no policy), and extensive support for crafting your own policies using the insanely great Lua scripting language.

Note that although there is a single Lua configuration file, the canonicalize, reset, report and allow functions run in different lua states from the rest of the configuration. This mostly "just works", but may lead to unexpectd behaviour such as running Lua commands at the server Lua prompt, and getting multiple answers (because Lua commands are passed to all Lua states).


-- set up the things we want to track
field_map = {}
-- use hyperloglog to track cardinality of (failed) password attempts
field_map["diffFailedPasswords"] = "hll"
-- track those things over 6x10 minute windows
newStringStatsDB("OneHourDB", 600, 6, field_map)

-- this function counts interesting things when "report" is invoked
function twreport(lt)
	sdb = getStringStatsDB("OneHourDB")
	if (not lt.success)
	   sdb:twAdd(lt.remote, "diffFailedPasswords", lt.pwhash)
	   addrlogin = lt.remote:tostring() .. lt.login
	   sdb:twAdd(addrlogin, "diffFailedPasswords", lt.pwhash)

function allow(lt)
	sdb = getStringStatsDB("OneHourDB")
	if(sdb:twGet(lt.remote, "diffFailedPasswords") > 50)
		return -1, "", "", {} -- BLOCK!
	// concatenate the IP address and login string
	addrlogin = lt.remote:tostring() .. lt.login	
	if(sdb:twGet(addrlogin, "diffFailedPasswords") > 3)
		return 3, "tarpitted", "diffFailedPasswords", {} -- must wait for 3 seconds

	return 0, "", "", {} -- OK!

Many more metrics are available to base decisions on. Some example code is in wforce.conf, and more extensive examples are in wforce.conf.example. For full documentation, use "man wforce.conf".

To report (if you configured with 'webserver("", "secret")'):

$ for a in {1..101}
    curl -X POST -H "Content-Type: application/json" --data '{"login":"ahu", "remote": "", "pwhash":"1234'$a'", "success":"false"}' \ -u wforce:secret

This reports 101 failed logins for one user, but with different password hashes.

Now to look up if we're still allowed in:

$ curl -X POST -H "Content-Type: application/json" --data '{"login":"ahu", "remote": "", "pwhash":"1234"}' \ -u wforce:super
{"status": -1, "msg": "diffFailedPasswords"}

It appears we are not!

You can also provide additional information for use by weakforce using the optional "attrs" object. An example:

$ curl -X POST -H "Content-Type: application/json" --data '{"login":"ahu", "remote": "",
"pwhash":"1234", "attrs":{"attr1":"val1", "attr2":"val2"}}' \ -u wforce:super
{"status": 0, "msg": ""}

An example using the optional attrs object using multi-valued attributes:

$ curl -X POST -H "Content-Type: application/json" --data '{"login":"ahu", "remote": "",
"pwhash":"1234", "attrs":{"attr1":"val1", "attr2":["val2","val3"]}}' \ -u wforce:super
{"status": 0, "msg": ""}

There is also a command to reset the stats for a given login and/or IP Address, using the 'reset' command, the logic for which is also implemented in Lua. The default configuration for reset is as follows:

function reset(type, login, ip)
	 sdb = getStringStatsDB("OneHourDB")
	 if (string.find(type, "ip"))
	 if (string.find(type, "login"))
	 if (string.find(type, "ip") and string.find(type, "login"))
		iplogin = ip:tostring() .. login
	 return true

To test it out, try the following to reset the login 'ahu':

$ curl -X POST -H "Content-Type: application/json" --data '{"login":"ahu"}'\ -u wforce:super
{"status": "ok"}

You can reset IP addresses also:

$ curl -X POST -H "Content-Type: application/json" --data '{"ip":""}'\ -u wforce:super
{"status": "ok"}

Or both in the same command (this helps if you are tracking stats using compound keys combining both IP address and login):

$ curl -X POST -H "Content-Type: application/json" --data '{"login":"ahu", "ip":"FE80::0202:B3FF:FE1E:8329"}'\ -u wforce:super
{"status": "ok"}

Finally there is a "ping" command, to check the server is up and answering requests:

$ curl -X GET -u wforce:super
{"status": "ok"}


Available over TCP/IP, like this:


Launch wforce as a daemon (wforce --daemon), to connect, run wforce -c. Comes with autocomplete and command history. If you put an actual IP address in place of, you can use the same config to listen and connect remotely.

To get some stats, try:

> stats()
40 reports, 8 allow-queries, 40 entries in database

The wforce manpage describes the command-line options and all the possible console commands in more detail.


Wforce accepts reports with 4 mandatory fields plus multiple optional fields.


  • login (string): the user name or number or whatever
  • remote (ip address): the address the user arrived on
  • pwhash (string): a highly truncated hash of the password used
  • success (boolean): was the login a success or not?


  • policy_reject (boolean) - If the login was not successful only because of a policy-based reject from wforce (i.e. the username and password were correct).
  • attrs (json object): additional information about the login. For example, attributes from a user database.
  • device_id (string) - A string that represents the device that the user logged in from. For HTTP this would typically be the User-Agent string, and for IMAP it would be the IMAP client ID command string.
  • protocol (string) - A string representing the protocol used to login, e.g. "http", "imap", "pop3".
  • tls (boolean) - Whether or not the login was secured with TLS.

The entire HTTP API is documented using the excellent OpenAPI (swagger) specification.

The pwhash field deserves some clarification. In order to distinguish actual brute forcing of a password, and repeated incorrect but identical login attempts, we need some marker that tells us if passwords are different.

Naively, we could hash the password, but this would spread knowledge of secret credentials beyond where it should reasonably be. Even if we salt and iterate the hash, or use a specific 'slow' hash, we're still spreading knowledge.

However, if we take any kind of hash and truncate it severely, for example to 12 bits, the hash tells us very little about the password itself - since one in 4096 random strings will match it anyhow. But for detecting multiple identical logins, it is good enough.

For additional security, hash the login name together with the password - this prevents detecting different logins that might have the same password.

NOTE: wforce does not require any specific kind of hashing scheme, but it is important that all services reporting successful/failed logins use the same scheme!

When in doubt, try:


Which denotes to take the first 12 bits of the hash of the concatenation of a secret, the login, a 0 byte and the password. Prepend 4 0 bits to get something that can be expressed as two bytes.

API Calls

We can call 'report', and 'allow' commands. The optional 'attrs' field enables the client to send additional data to weakforced.

To report, POST to /?command=report a JSON object with fields from the LoginTuple as described above.

To request if a login should be allowed, POST to /?command=allow, again with the LoginTuple. The result is a JSON object with a "status" field. If this is -1, do not perform login validation (i.e. provide no clue to the client if the password was correct or not, or even if the account exists).

If 0, allow login validation to proceed. If a positive number, sleep this many seconds until allowing login validation to proceed.

Custom API Endpoints

You can create custom API commands (REST Endpoints) using the following configuration:

setCustomEndpoint("custom", customfunc)

which will create a new API command "custom", which calls the Lua function "customfunc" whenever that command is invoked. Parameters to custom commands are always in the same form, which is key-value pairs wrapped in an 'attrs' object. For example, the following parameters sents as json in the message body would be valid:

{ "attrs" : { "key" : "value" }}

Custom functions return values are also key-value pairs, this time wrapped in an 'r_attrs' object, along with a boolean success field, for example:

{ "r_attrs" : { "key" : "value" }, "success" : true}

An example configuration for a custom API endpoint would look like:

function custom(args)
	for k,v in pairs(args.attrs) do
		infoLog("custom func argument attrs", { key=k, value=v });
	-- return consists of a boolean, followed by { key-value pairs }
	return true, { key=value }
setCustomEndpoint("custom", custom)

An example curl command would be:

% curl -v -X POST -H "Content-Type: application/json" --data
  '{"attrs":{"login1":"ahu", "remote": "",  "pwhash":"1234"}}' -u wforce:super
{"r_attrs": {}, "success": true}


It is possible to configure webhooks, which get called whenever specific events occur. To do this, use the "addWebHook" configuration command. For example:

config_keys["url"] = ""
config_keys["secret"] = "verysecretcode"
events = { "report", "allow" }
addWebHook(events, config_keys)

The above will call the webhook at the specified url, for every report and allow command received, with the body of the POST containing the original json data sent to wforce. For more information use "man wforce.conf" and "man wforce_webhook".

Custom WebHooks

Custom webhooks can also be defined, which are not invoked based on specific events, but instead from Lua. Configuration is similar to normal webhooks:

config_keys["url"] = ""
config_keys["secret"] = "verysecretcode"
config_keys["content-type"] = "application/json"
addCustomWebHook("mycustomhook", config_keys)

However, the webhook will only be invoked via the Lua "runCustomWebHook" command, for example:

runCustomWebHook(mycustomhook", "{ \"foo\":\"bar\" }")

The above command will invoke the custom webhook "mycustomhook" with the data contained in the second argument, which is simply a Lua string. No parsing of the data is performed, however the Content-Type of the webhook, which defaults to application/json can be customized as shown above.


Blacklisting capability is provided via either REST endpoints or Lua commands, to add/delete IP addresses, logins or IP:login tuples from the Blacklist. Blacklist information can be replicated (see below), and also optionally persisted in a Redis DB. Use "man wforce.conf" to learn more about the blacklist commands.

Load balancing: siblings

For high-availability or performance reasons it may be desireable to run multiple instances of wforce. To present a unified view of status however, these instances then need to share data. To do so, wforce implements a simple knowledge-sharing system.

The original version of wforce simply broadcast all received report tuples (best effort, UDP) to all siblings. However the latest version only broadcasts incremental changes to the underlying state databases, namely the stats dbs and the blacklist.

The sibling list is parsed such that we don't broadcast messages to ourselves accidentally, and can thus be identical across all servers.

Even if you configure siblings, stats db data is not replicated by default. To do this, use the "twEnableReplication()" command on each stats db for which you wish to enable replication. Blacklist information is automatically replicated if you have configured siblings.

To define siblings, use:


The first line sets the authentication and encryption key for our sibling communications. To make your own key (recommended), run makeKey() on the console and paste the output in all your configuration files.

This last line configures that we also listen to our other siblings (which is nice). The default port is 4001, the protocol is UDP.

To view sibling stats:

> siblings()
Address                             Sucesses  Failures     Note                   18        7                   25        0                   0         0            Self

With this setup, several wforces are all kept in sync, and can be load balanced behind (for example) haproxy, which incidentally can also offer SSL.

GeoIP2 Support

GeoIP support is provided using the GeoIP2 Maxmind APIs DBs (i.e. DBs ending in .mmdb). This is the preferred integration to use, as support for GeoIP Legacy DBs will be discontinued by Maxmind in 2019.

GeoIP2 DBs are represented by a Lua object that is created with the following call:

newGeoIP2DB("Name", "/path/to/file.mmdb")

The Lua object is retrieved with the following call:

local mygeodb = getGeoIP2DB("Name")

You can then lookup infomation using the following calls:

  • lookupCountry() - Returns the 2 letter country code associated with the IP address
  • lookupISP() - Returns the name of the ISP associated with the IP address (requires the Maxmind ISP DB, which is only available on subscription)
  • lookupCity - Rather than only returning a city name, this call returns a Lua table which includes the following information:
    • country_code
    • country_name
    • region
    • city
    • postal_code
    • continent_code
    • latitude
    • longitude

For example:

local geoip_data = mygeodp:lookupCity(newCA(""))

Legacy GeoIP Support

Support for legacy GeoIP databases (i.e. ending in .dat) is deprecated, since Maxmind will be discontinuing support for them in 2019.

Three types of GeoIP lookup are supported:

  • Country lookups - Initialized with initGeoIPDB() and looked up with lookupCountry()
  • ISP Lookups - Initialized with initGeoIPISPDB() and looked up with lookupISP()
  • City Lookup - Initialized with initGeoIPCityDB() and looked up with lookupCity()

The Country and ISP lookups return a string, while lookupCity() returns a Lua map consisting of the following keys:

  • country_code
  • country_name
  • region
  • city
  • postal_code
  • continent_code
  • latitude
  • longitude

For example:

local geoip_data = lookupCity(newCA(""))

When a DB is initialized, wforce attempts to open both v4 and v6 versions of the database. If either is not found an error is thrown, so make sure both ipv4 and v6 versions of each DB are installed.

Additionally, when using the free/lite versions of the databases, you may see errors such as "initGeoIPCityDB(): Error initialising GeoIP (No geoip v6 city db available)". This is usually because the filenames for the "lite" DBs are not the same as the expected filenames for the full DBs, specifically all files must start with GeoIP rather than GeoLite. Creating symbolic links to the expected filenames will fix this problem, for example:

ln -s GeoLiteCityv6.dat GeoIPCityv6.dat