[RFC] Risk Score Extensions - Stage 1

rfcs/text/0042-risk-score-extensions.md

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 This RFC seeks to extend the [existing risk fields](https://www.elastic.co/guide/en/ecs/current/ecs-risk.html) [(RFC 0031)](https://github.com/elastic/ecs/pull/2048) to support new/extended Risk Score investigation workflows. The workflows that this RFC intends to enable include all those described in 0031, along with the following:
 
 1. Risk Score Explainability
@@ -24,16 +21,50 @@ This RFC seeks to extend the [existing risk fields](https://www.elastic.co/guide
     * These categories' definitions may be _extended_ in the future to include new data sources
   * Due to the above category traits, we need to come up with a naming convention for these categorical score fields that allows them to be extended without invalidating the existing field names.
 
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 ## Fields
 
+I'll enumerate the fields being introduced here grouped by their motivation/goal:
+
+### Identifier Fields
+These fields are intended to allow future extensibility of our concept of an "identifier." Currently, we leverage two such fields: `host.name` and `user.name`, to group documents for the purposes of risk scoring, but we definitely imagine this being extended in the future to allow multiple such fields for hosts and users, or more simply to allow administrators to configure fields other than those above. The presence of these two fields allows us to audit/explain how a particular risk score was identified.
+
+* `id_field`
+* `id_value`
+
+
+### Risk Category Fields
+Some of the context here was discussed in Stage 0; please read the above for that. More specifically, these fields seek to provide the category contributions to the score, and the number of risk inputs in that category, across each of the five proposed categories:
+
+* `category_1_score`
+* `category_1_count`
+* `category_2_score`
+* `category_2_count`
+* `category_3_score`
+* `category_3_count`
+* `category_4_score`
+* `category_4_count`
+* `category_5_score`
+* `category_5_count`
+
+### Risk Explainability
+Beyond the per-category explanations, these fields' purpose is to provide more insight/data for the analyst to further investigate the components of the risk score.
+
+* `risk.inputs`
+  * Generally, these objects are meant as a convenience for one investigating risk; they are the "most risky" inputs as determined by the risk engine, and serve as a shortcut to further investigation.
+* `inputs.id`, `inputs.index`
+  * These fields allow one to uniquely identify the original risk input document.
+* `inputs.category`, `inputs.risk_score`
+  * More "convenience" fields that could also be discovered in the original risk input document.
+* `inputs.description`
+  * These field is intended to be a precursor to what we are referring to as "Risk Reasons," which seek to aggregate/present multiple risk inputs in an easier to consume/analyze format.
+* `notes`
+  * Miscellaneous text field intended to provide more details that cannot be presented in the other fields.
+
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@@ -44,15 +75,11 @@ Stage 2: Add or update all remaining field definitions. The list should now be e
 
 ## Usage
 
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-Stage 1: Describe at a high-level how these field changes will be used in practice. Real world examples are encouraged. The goal here is to understand how people would leverage these fields to gain insights or solve problems. ~1-3 paragraphs.
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+We intend to leverage these new fields as part of the new implementation of the Risk Engine within Kibana. In fact, we have already written [the code that uses these fields](https://github.com/elastic/kibana/pull/161503/files#diff-75c9ad5c7d4b56459148fd9c08cb6cb229e932ea00f3e39725134ba429ad2915R66-R85), albeit not in the exact form described here. Beyond the existing ECS `risk` fields, the new implementation mainly seeks to improve explainability of individual risk scores.
 
 ## Source data
 
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+The new Risk Engine will initially use Detection Engine Alerts as inputs to its scoring mechanism. However, we intend also to allow ingestion from the other Risk Categories described here, provided that they conform to the appropriate schema. Said schema is outside of the scope of this RFC, but based on the current implementation all we will need are a `score` field and a `category` field in order to ingest any arbitrary document.
 
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@@ -74,6 +101,13 @@ The goal here is to research and understand the impact of these changes on users
 
 ## Concerns
 
+There are two broad concerns at this stage:
+
+1. Category fields introducing a new "ordered" pattern
+  * Rather than having either an array of objects, or an explicit `nested` field type, both of which allow an arbitrary number of items, we're instead opting to add 10 explicit fields (five explicit categories, each with two fields) under the _assumption_ that we won't extend the number of categories further. We have a bit of wiggle room (i.e. six categories, 12 fields wouldn't be out of question), but this is not a scalable solution if we need a large number of categories. However, that is only a potential future issue, and we can likely reevaluate and address it if/when it arises.
+2. Mapping of `inputs` as a simple `object`
+  * The biggest motivation for this choice is to avoid the performance/storage/syntax complexities that come with a `nested` mapping, but we also don't have any feature requirements that would currently necessitate `inputs` being `nested`.
+
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@@ -91,19 +125,8 @@ Stage 3: Document resolutions for all existing concerns. Any new concerns should
 The following are the people that consulted on the contents of this RFC.
 
 * @rylnd | author
-* @SourinPaul | SME / EA product manager
-
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+* @SourinPaul | sponsor
+* @ebeahan | reviewer
 
 
 ## References
@@ -117,6 +140,7 @@ e.g.:
 <!-- An RFC should link to the PRs for each of it stage advancements. -->
 
 * Stage 0: https://github.com/elastic/ecs/pull/2232
+* Stage 1: https://github.com/elastic/ecs/pull/2236
 
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 * Stage 1: https://github.com/elastic/ecs/pull/NNN

rfcs/text/0042/risk.yml

@@ -0,0 +1,161 @@
+---
+- name: risk
+  title: Risk information
+  group: 2
+  short: Fields for describing risk score and level.
+  beta: >
+    These fields are in beta and are subject to change.
+  description: >
+    Fields for describing risk score and risk level of entities such as hosts and users.
+    These fields are not allowed to be nested under `event.*`. Please continue to use
+    `event.risk_score` and `event.risk_score_norm` for event risk.
+  reusable:
+    top_level: false
+    expected:
+      - host
+      - user
+  type: group
+  fields:
+    - name: id_field
+      level: extended
+      type: keyword
+      example: host.name
+      description: >
+        The name of the ECS field that identifies the entity. Typically, hosts use `host.name` and users use `user.name`.
+    - name: id_value
+      level: extended
+      type: keyword
+      example: host-001.local
+      description: >
+        The entity's identifier value that was used to calculate risk. Typically, hosts use values from `host.name` and users use values from `user.name`.
+    - name: category_1_score
+      level: extended
+      type: float
+      example: 33.0
+      description: >
+        The contribution of Category 1 to the overall risk score (`calculated_score`).
+
+        Risk Categories logically group risk inputs from various domain use cases. Category 1 includes Alerts, namely from Kibana's Detection Engine.
+    - name: category_1_count
+      level: extended
+      type: long
+      example: 3291
+      description: >
+        The number of risk input documents that contributed to the Category 1 score.
+
+        Risk Categories logically group risk inputs from various domain use cases. Category 1 includes Alerts, namely from Kibana's Detection Engine.
+    - name: category_2_score
+      level: extended
+      type: float
+      example: 35.0
+      description: >
+        The contribution of Category 2 to the overall risk score (`calculated_score`).
+
+        Risk Categories logically group risk inputs from various domain use cases. Category 2 includes inputs from Posture Management.
+    - name: category_2_count
+      level: extended
+      type: long
+      example: 1921
+      description: >
+        The number of risk input documents that contributed to the Category 2 score.
+
+        Risk Categories logically group risk inputs from various domain use cases. Category 2 includes inputs from Posture Management.
+    - name: category_3_score
+      level: extended
+      type: float
+      example: 25.0
+      description: >
+        The contribution of Category 3 to the overall risk score (`calculated_score`).
+
+        Risk Categories logically group risk inputs from various domain use cases. Category 3 includes inputs from Vulnerabilities.
+    - name: category_3_count
+      level: extended
+      type: long
+      example: 4920
+      description: >
+        The number of risk input documents that contributed to the Category 3 score.
+
+        Risk Categories logically group risk inputs from various domain use cases. Category 3 includes inputs from Vulnerabilities.
+    - name: category_4_score
+      level: extended
+      type: float
+      example: 55.0
+      description: >
+        The contribution of Category 4 to the overall risk score (`calculated_score`).
+
+        Risk Categories logically group risk inputs from various domain use cases. Category 4 includes Entity Contexts.
+    - name: category_4_count
+      level: extended
+      type: long
+      example: 1308
+      description: >
+        The number of risk input documents that contributed to the Category 4 score.
+
+        Risk Categories logically group risk inputs from various domain use cases. Category 4 includes Entity Contexts.
+    - name: category_5_score
+      level: extended
+      type: float
+      example: 75.0
+      description: >
+        The contribution of Category 5 to the overall risk score (`calculated_score`).
+
+        Risk Categories logically group risk inputs from various domain use cases. Category 5 contains inputs from Anomalies.
+    - name: category_5_count
+      level: extended
+      type: long
+      example: 14922
+      description: >
+        The number of risk input documents that contributed to the Category 5 score.
+
+        Risk Categories logically group risk inputs from various domain use cases. Category 5 contains inputs from Anomalies.
+    - name: inputs
+      level: extended
+      type: object
+      normalize: array
+      description: >
+        An array of the top risk input documents that contributed to the overall risk score.
+      fields:
+        - name: id
+          level: extended
+          type: keyword
+          description: >
+            The identifier (_id) of the risk input document.
+        - name: index
+          level: extended
+          type: keyword
+          description: >
+            The index (`_index`) of the risk input document.
+        - name: category
+          level: extended
+          type: keyword
+          example: category_1
+          description: >
+            The risk category of the risk input document.
+        - name: description
+          level: extended
+          type: keyword
+          example: "Generated from Detection Engine Rule: Malware Prevention Alert"
+          description: >
+            A human-readable description of the risk input document.
+          multi_fields:
+            - type: match_only_text
+              name: text
+        - name: risk_score
+          level: extended
+          type: float
+          example: 30.0
+          description: >
+            The weighted risk score of the risk input document.
+        - name: timestamp
+          level: extended
+          type: date
+          example: '2019-08-16T01:40:25Z'
+          description: >
+            The @timestamp of the risk input document.
+    - name: notes
+      level: extended
+      type: keyword
+      normalize: array
+      example: ["This score was boosted due to the entity being a host."]
+      description: >
+        Notes about the risk score and/or its calculation.