Writing Simple Detections

Construct YAML detections in the CLI workflow

Overview

Simple Detections can be created in the CLI workflow in YAML, in addition to being created in the Simple Detection Builder in the Console.

Simple Detections created in the CLI workflow, then uploaded to Panther, can be viewed and edited in the Simple Detection builder in the Console. This may be valuable if members of your team have varying levels of experience with YAML.

Simple detections can be used in detection derivation.

If you aren't sure whether to write detections locally as Simple Detections (in YAML) or Python detections, see the Using Python vs. Simple Detections YAML section.

If your team uses the CLI workflow to manage detection content, the changes made to detections using the Simple Detection builder in the Console will be overwritten on next upload (except for Inline Filters created in the Console, which will be preserved).

If you create or edit detections using the Simple Detection builder in the Console, copy the resulting YAML representation and include it in your local detections files, in order to prevent the changes from being overwritten on next upload.

Limitations of Simple Detections YAML

• Scheduled rules and policies cannot be created as Simple Detections.

  • Only rules can be created in YAML.

• Panther-managed Simple Detections are not yet available.

  • It is possible, however, to use Panther-managed Python detections alongside your own Simple Detections.

• Many helper functions available in Python, including those for specific log sources, are not represented in YAML.

  • Some global helpers have been converted into YAML keys, e.g., deep_get() is DeepKey.

• It is not possible to make external API calls in Simple Detections, including to fetch values from your Dynamo KV store to use caching.

How to create a Simple Detection (rule) in YAML

Creating a Simple Detection rule in the CLI workflow

If you're writing Simple Detections locally (instead of in the Simple Detection Builder in the Console), we recommend managing your local detection files in a version control system like GitHub or GitLab.

Folder setup

If you group your rules into folders, each folder name must contain rules in order for them to be found during upload (using either PAT or the bulk uploader in the Console).

We recommend grouping rules into folders based on log/resource type, e.g., suricata_rules or aws_s3_policies.

File setup

Each rule and scheduled rule consists of:

• A YAML specification file (a file with a .yml extension) containing the detection logic, as well as metadata attributes of the detection.

  • This file has similar syntax to the Python YAML files, with some additional keys.

Simple Detection rules contain lists of boolean logic called match expressions that detect suspicious behaviors. Returning a value of True indicates suspicious activity, which triggers an alert.

Learn more about Simple Detection YAML syntax, and see a complete list of required and optional YAML fields below.

• Create a YAML file (e.g. my_new_rule.yml) using the template below (including a top-level Detection key):

  AnalysisType: rule
  DedupPeriodMinutes: 60 # 1 hour
  DisplayName: Example Rule to Check the Format of the Spec
  Enabled: true
  RuleID: Type.Behavior.MoreContext
  Severity: High
  LogTypes:
    - LogType.GoesHere
  Reports:
    ReportName (like CIS, MITRE ATT&CK):
      - The specific report section relevant to this rule
  Tags:
    - Tags
    - Go
    - Here
  Description: >
    This rule exists to validate the CLI workflows of the Panther CLI
  Runbook: >
    First, find out who wrote this the spec format, then notify them with feedback.
  Reference: https://www.a-clickable-link-to-more-info.com
  Detection:
    - KeyPath: hostName
      Condition: Contains
      Value: prod

After this rule is uploaded to Panther, it will be viewable in the Console in the Simple Detection builder.

Simple Detection YAML syntax

Each custom Simple Detection can be composed of:

• Detection key

  Detection: 

• Filter key

  InlineFilters: 

• Metadata keys

  AnalysisType: 
  Enabled: 
  CreateAlert: 
  RuleID:
  CreatedBy:
  LogTypes: 
  Reports: 
  Tags: 
  Tests: 

• Alert keys (dynamic)

  DynamicSeverities: 
  AlertTitle: 
  AlertContext: 
  GroupBy: 

• Alert keys (static)

  Severity:
  Description:
  DedupPeriodMinutes:
  Threshold: 
  DisplayName:
  OutputIds:
  Reference:
  Runbook:
  SummaryAttributes: 

Learn more about each of these keys, including which are required and optional, in the Simple Detection rule specification reference below.

Detection

Within the Detection key, include one or more match expressions.

InlineFilters

Learn more about using InlineFilters in Simple Detections on Modifying Detections with Inline Filters.

Dynamic alert keys in Simple Detections

Alert fields are fields in a Simple Detection definition that are applicable to the alerts generated by that detection.

Alert fields can be static or dynamic. With static alert fields, you provide a set value in the detection definition, which does not change based on the incoming event. Dynamic alert fields, however, can use information in the event to determine the value.

If you are using alert deduplication, the first event to match the detection is used by these alert keys.

DynamicSeverities

Use DynamicSeverities to dynamically set the severity of an alert generated by a match on this detection. This field is dynamic because you can use values from the event to determine the severity.

When DynamicSeverities is present, its value overrides the value of the Severity key. Severity is still required, and its value will be the fallback value if there are no matches on any of the match expressions contained within DynamicSeverities.

Within the DynamicSeverities key, include one or more ChangeTo keys, each with a corresponding Conditions key. The value of ChangeTo should be one of the alert severities. The ChangeTo blocks are evaluated in order, from top to bottom, and evaluation stops once a match has been found.

Within Conditions, include one or more match expressions. The Conditions list has the following limitations:

• No list comprehension, multi-key, or absolute match expressions may be used.

• No combinators may be used.

Example:

DynamicSeverities:
  - ChangeTo: CRITICAL
    Conditions:
      - Key: status
        Condition: Equals
        Value: severe
  - ChangeTo: MEDIUM
    Conditions:
      - KeyPath: user.name
        Condition: StartsWith
        Value: admin_
      - DeepKey:
          - user
          - roles
        Condition: Contains
        Value: wheel

AlertTitle

Use AlertTitle to dynamically set the title of an alert generated by a match on this detection. This field is dynamic because you can use values from the event in the title.

The value of AlertTitle should be a string. You can reference event values by using curly braces. Inside the curly braces, use JSON path syntax.

Example:

AlertTitle: "User {actor.username} impersonated {target.username} at {time}"

AlertContext

AlertContext lets you identify event data to pass onto generated alerts, formatted as a dictionary.

Within AlertContext, include one or more KeyName and KeyValue pairs. KeyName takes a string of your choice, which will become the key in the alert context dictionary. Within KeyValue, use a key specifier to indicate an event key—its value will be the value in the alert context dictionary.

KeyValue values must be JSON-compliant. Examples of non-compliant values include Python's nan, inf, and -inf.

Example:

AlertContext:
  - KeyName: ip
    KeyValue:
      Key: sourceIP
  - KeyName: user
    KeyValue:
      DeepKey:
        - user
        - username
  - KeyName: resource
    KeyValue:
      KeyPath: resource.arns

GroupBy

GroupBy sets the deduplication string for your detection. Learn more about deduplication, including the order of precedence for how the deduplication string is set, on Rules and Scheduled Rules.

Within the GroupBy key, include a list of one or more event keys defined with key specifiers.

Example:

GroupBy:
  - Key: sourceIP
  - KeyPath: user.name
  - KeyPath: resource.arn

The values of the keys provided under GroupBy are joined with a colon to form the deduplication string. The outputted deduplication string for the above example would be:

<value of sourceIP>:<value of user.name>:<value of resource.arn>

Simple Detection rule specification reference

The table below contains all available YAML keys for Simple Detections. Required fields are in bold.

If you are writing a Python rule, instead see the Python rule specification reference.