.. _Plugin Examples: Examples ======== How to properly code a plugin is described in the reminder of this section. However, before delving into the technical details, a couple of examples are presented to give the reader a quick and direct overview of ntopng plugins. .. _Blacklisted Flows: Blacklisted Flows ----------------- Aim of this plugin is to trigger an alert every time a flow is found to have its client or server (or both) in a blacklist. ntopng loads custom and predefined blacklists as explained in :ref:`Category Lists`. This plugin tests each flow for its client and server, and possibly create an alert when they are found to be blacklisted. Full plugin sources are available on `GitHub blacklisted flows plugin page `_. The complete structure of the plugin is as follows: .. code:: bash blacklisted |-- manifest.lua |-- user_scripts `-- flow `-- blacklisted.lua |-- alert_definitions `-- alert_flow_blacklisted.lua |-- status_definitions `-- status_blacklisted.lua As it can be seen from the file system tree, a plugin is a set of Lua files, placed in pre-defined sub-directories. The root directory, :code:`blacklisted`, should carry a name which is representative for the plugin. This directory contains other sub-directories and a :code:`manifest.lua` file, a plugin manifest containing basic plugin information: .. code:: lua -- -- (C) 2019-20 - ntop.org -- return { title = "Blacklisted Hosts", description = "Detects blacklisted hosts and triggers alerts", author = "ntop", version = 1, dependencies = {}, } Sub-directories :code:`alert_definitions` and :code:`status_definitions` contain Lua scripts which are necessary to tell ntopng the plugin is going to set certain flow status and trigger certain alerts. In this specific plugin, :code:`alert_flow_blacklisted.lua` tells ntopng the plugin is willing to create an alert for blacklisted flows. Similarly, :code:`status_blacklisted.lua` tells ntopng the plugin is going to set a blacklisted status for certain flows. Those two directories, as said by their names, contain just definitions of alerts and flow status, the actual logic stays in directory :code:`user_scripts`. As this plugin requires flows to carry on its task, directory :code:`user_scripts` with the logic must contain a subdirectly :code:`flow`, which, in turn, contains file :code:`blacklisted.lua`. ntopng knows it has to execute :code:`blacklisted.lua` agains each flow it sees because :code:`blacklisted.lua` is found under the :code:`flow` directory. Let's have a look at the contents of :code:`blacklisted.lua`: .. code:: lua -- -- (C) 2019-20 - ntop.org -- local flow_consts = require("flow_consts") -- ################################################################# local script = { -- NOTE: hooks defined below hooks = {}, gui = { i18n_title = "flow_callbacks_config.blacklisted", i18n_description = "flow_callbacks_config.blacklisted_description", } } -- ################################################################# function script.hooks.protocolDetected(now) if flow.isBlacklisted() then local info = flow.getBlacklistedInfo() local flow_score = 100 local cli_score, srv_score if info["blacklisted.srv"] then cli_score = 100 srv_score = 5 else cli_score = 5 srv_score = 10 end flow.triggerStatus(flow_consts.status_types.status_blacklisted.status_id, info, flow_score, cli_score, srv_score) end end -- ################################################################# return script The first thing to observe, is that :code:`blacklisted.lua` contains a single :code:`function` with a predefined name :code:`script.hooks.protocolDetected`. This name tells ntopng to execute the plugin for every flow, as soon as the flow has its :code:`protocolDetected`, which is one of the several events plugins can attach to. The body of the function has access to a :code:`flow` Lua table, with several methods available to be called, among which :code:`flow.isBlacklisted()`. Method :code:`flow.isBlacklisted()` returns a boolean which is either true or false, depending on whether any of the client or server is blacklisted. As this plugin wants to trigger an alert then the flow is blacklisted, method is called and tested in the first :code:`if`. When the flow is blacklisted and the method returns true, a couple of scores are computed. Scores are numbers associated to the client and server of the flow and attempt to summarize how critical is the issue for both the client and the server. So why does the client score is much higher when the server is blacklisted? Because in this case it is assumed that the client is infected and attempting to contact malicious hosts. When is the client to be blacklisted, then it may just be a scan attempt by a malicious host and thus the score is lower. Once the scores have been computed, the function calls :code:`flow.triggerStatus`. This is the actual call that causes ntopng to set the blacklisted status and trigger an alert! This call wants the two scores as parameters, along with the flow status defined in :code:`status_definitions` and an info table which contains certain extra details and description of the flow blacklisted peers. From this point on, the flow will appear as alerted and with status blacklisted in the ntopng web UI, along with the scores specified for its client and server. That is pretty much all to create a flow script! A quick note on the :code:`gui` section. It has just a title and a description that will be used by ntopng in the web UI, to allow a user to enable/disable the plugin. .. _Flow Flooders: Flow Flooders ------------- Aim of this plugin is to trigger an alert when an host or a network is having more than a predefined number of flows over a minute. As an host can be either the client or the server of a flow, two types of alerts are meaningful in this case, namely, a flow flood attacker alert and a flow flood victim alert. The same reasoning can be applied to networks as well. A network can either be considered a flow flood attacker or a flow flood victim, depending on whether its host are the clients or servers of the monitored flows. The predefined threshold can be configured from the web UI so that one can tune it on a host-by-host or CIDR basis. Indeed, a threshold which is meaningful for an host is not necessarily meaningful for another host. Full plugin sources are available on `GitHub flow flood plugin page `_. The complete structure of the plugin is as follows: .. code:: bash flow_flood/ |-- manifest.lua |-- alert_definitions | `-- alert_flows_flood.lua `-- user_scripts |-- host | |-- flow_flood_attacker.lua | `-- flow_flood_victim.lua `-- network `-- flow_flood_victim.lua From the file system tree, it can be seen that the plugin is self-contained in :code:`flow_flood`, a directory which carries a name representative for the plugin. The :code:`manifest.lua` script, a sort of manifest for the plugin, contains basic information and description .. code:: lua -- -- (C) 2019-20 - ntop.org -- return { title = "Flow Flood detector", description = "Detects flow flood attacks and triggers alerts", author = "ntop", version = 1, dependencies = {}, } This plugin doesn't work on flows, so no :code:`flow` directory is present under :code:`user_scripts` and no :code:`status_definitions` is necessary as it has been seen for the `Blacklisted Flows`_. However, as this plugin generates alerts, :code:`alert_flows_flood.lua` is needed under :code:`alert_definitions` to tell ntopng about this. The logic stays under :code:`user_scripts` which has two sub-directories: :code:`host` and :code:`network`, each one containing lua files with the logic necessary to trigger the alert. ntopng will execute scripts under the :code:`host` directory on every host and scripts under the :code:`network` directory on every network. Let's have a closer look at :code:`host` s :code:`flow_flood_attacker.lua`, of the scripts executed on hosts (the other Lua script are similar): .. code:: lua -- -- (C) 2019-20 - ntop.org -- local alerts_api = require("alerts_api") local alert_consts = require("alert_consts") local user_scripts = require("user_scripts") local script = { default_enabled = true, default_value = { -- "> 50" operator = "gt", threshold = 50, }, -- This script is only for alerts generation is_alert = true, -- See below hooks = {}, gui = { i18n_title = "entity_thresholds.flow_attacker_title", i18n_description = "entity_thresholds.flow_attacker_description", i18n_field_unit = user_scripts.field_units.flow_sec, input_builder = "threshold_cross", field_max = 65535, field_min = 1, field_operator = "gt"; } } -- ################################################################# function script.hooks.min(params) local ff = host.getFlowFlood() local value = ff["hits.flow_flood_attacker"] or 0 -- Check if the configured threshold is crossed by the value and possibly trigger an alert alerts_api.checkThresholdAlert(params, alert_consts.alert_types.alert_flows_flood, value) end -- ################################################################# return script The first thing to observe is that the script has only one function with a pre-defined name :code:`script.hooks.min`. This name tells ntopng to call this function on every host, *every minute*. The body of the function is fairly straightforward. It access a Lua table :code:`host`, with several methods available to be called. This Lua table contains references and methods that can be called on every host of the system. As the aim of this plugin is to determine whether the host is a flow flooder, method :code:`host.getFlowFlood()` is called which contains flooding information. Then, a :code:`value` is read from key :code:`hits.flow_flood_attacker` of the returned table. At this point, checking whether to trigger an alert or not, depending on whether the :code:`value` is above the pre-defined threshold, is up to the ntopng engine. From the perspective of this script, it suffices to call method :code:`alerts_api.checkThresholdAlert`. The method takes as input some params which falls outside the scope of this example, along with the type of alert that needs to be generated, and the actual :code:`value`. That is pretty much all. The ntopng engine will evaluate :code:`value` and possibly trigger the alert. Let's now have a closer look at the :code:`local script` table, which basically contains all the necessary configuraton, default values, and information to properly render a configuration page on the web UI. The table tells ntopng this script is enabled by default (:code:`default_enabled = true`) and also specify the default threshold values that should be used when no configuration has been input from the web UI (:code:`default_value`). Then, a boolean flag :code:`is_alert = true` is used to indicate the purpose of this user script is to generate alerts. An empty :code:`hooks` table is then specified. This table is used by ntopng to determine when a certain user script needs do be called. Remember the function :code:`script.hooks.min`? That actually adds the entry :code:`min` to the :code:`hooks` table so this plugin will be exected every minute! Finally, there is a :code:`gui` table to give ntopng instructions on how to render the configuration page of this user script. Basically, a title, description and unit of measure are indicated, along with an input builder and upper and lower bounds for the input. Input builders, as it will be seen in the next section, are used by ntopng to render the configuration of the user script.