Using the categorization fields

Serverless Stack

The event categorization fields work together to identify and group similar events from multiple data sources.

These general principles can help guide the categorization process:

• Events from multiple data sources that are similar enough to be viewed or analyzed together, should fall into the same event.category field.
• Both event.category and event.type are arrays and may be populated with multiple allowed values, if the event can be reasonably classified into more than one category and/or type.
• event.kind, event.category, event.type and event.outcome all have allowed values. This is to normalize these fields. Values that aren’t in the list of allowed values should not be used.
• Values of event.outcome are a very limited set to indicate success or failure. Domain-specific actions, such as deny and allow, that could be considered outcomes are not captured in the event.outcome field, but rather in the event.type and/or event.action fields.
• Values of event.category, event.type, and event.outcome are consistent across all values of event.kind.
• When a specific event doesn’t fit into any of the defined allowed categorization values, the field should be left empty.

The following examples detail populating the categorization fields and provides some context for the classification decisions.

This event from a firewall describes a successfully blocked network connection:

...
  {
    "source": {
      "address": "10.42.42.42",
      "ip": "10.42.42.42",
      "port": 38842
    },
    "destination": {
      "address": "10.42.42.1",
      "ip": "10.42.42.1",
      "port": 443
    },
    "rule": {
      "name": "wan-lan",
      "id": "default"
    },
    ...
    "event": {
      "kind": "event",
      "category": [
        "network"
      ],
      "type": [
        "connection",
        "denied"
      ],
      "outcome": "success",
      "action": "dropped"
    }
  }
...
		

1. Classifying as an event.
2. event.category categorizes this event as network activity.
3. The event was both an attempted network connection and was denied.
4. The blocking of this connection is expected. The outcome is a success from the perspective of the firewall emitting the event.
5. The firewall classifies this denied connection as dropped, and this value is captured in event.action.

A "denied" network connection could fall under different action values: "blocked", "dropped", "quarantined", etc. The event.action field captures the action taken as described by the source, and populating event.type:denied provides an independent, normalized value.

A single query will return all denied network connections which have been normalized with the same categorization values:

event.category:network AND event.type:denied
		

User alice attempts to add a user account, bob, into a directory service, but the action fails:

{
  "user": {
    "name": "alice",
    "target": {
      "name": "bob"
    }
  },
  "event": {
    "kind": "event",
    "category": [
      "iam"
    ],
    "type": [
      "user",
      "creation"
    ],
    "outcome": "failure"
  }
}
		

1. Again classifying as an event.
2. Categorized using iam for an event user account activity.
3. Both user and creation
4. The creation of a user account was attempted, but it was not successful.

A utility, such as a file integrity monitoring (FIM) application, takes inventory of a file but does not access or modify the file:

{
  "file": {
    "name": "example.png",
    "owner": "alice",
    "path": "/home/alice/example.png",
    "type": "file"
  },
  "event": {
    "kind": "event",
    "category": [
      "file"
    ],
    "type": [
      "info"
    ]
  }
}
		

1. Classifying as event.
2. The event is reporting on a file.
3. The info type categorizes purely informational events. The target file here was not accessed or modified.

The source data didn’t include any context around the event’s outcome, so event.outcome should not be populated.

An intrusion detection system (IDS) attempts to block a connection but fails. The event emitted by the IDS is considered an alert:

{
  "source": {
      "address": "10.42.42.42",
      "ip": "10.42.42.42",
      "port": 38842
    },
  "destination": {
      "address": "10.42.42.1",
      "ip": "10.42.42.1",
      "port": 443
  },
  ...
  "event": {
    "kind": "alert",
    "category": [
      "intrusion_detection",
      "network"
    ],
    "type": [
      "connection",
      "denied"
    ],
    "outcome": "failure"
  }
}
		

1. The IDS emitted this event when a detection rule generated an alert. The event.kind is set to alert.
2. With the event emitted from a network IDS device, the event is categorized both as network and intrusion_detection.
3. The alert event is a connection that was denied by the IDS' configuration.
4. The IDS experienced an issue when attempting to deny the connection. Since the action taken by the IDS failed, the outcome is set as failure.