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Writing Simple Detections

Construct Simple 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.
  • Many helper functions available in Python, including those for specific log sources, are not represented in YAML.
  • 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.
  • 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:
    RuleID:
    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:
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.
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.
Field Name
Description
Expected Value
AnalysisType
Indicates whether this analysis is a rule, scheduled_rule, policy, or global
rule
Enabled
Whether this rule is enabled
Boolean
RuleID
The unique identifier of the rule
String
LogTypes
The list of logs to apply this rule to
List of strings
Severity
Which severity an associated alert should have
One of the following strings: Info, Low, Medium, High, or Critical This field is overwritten by DynamicSeverities, but is required even if DynamicSeverities is defined
Detection
The list of match expressions to apply to the event data
Alternate severities based on custom sets of conditions
List of dynamic severity configurations, consisting of ChangeTo and Conditions fields. ChangeTo is a Severity value and Conditions is a list of match expressions.
Description
A brief description of the rule
String
GroupBy
Set of event values that will be used to deduplicate alerts by
List of event keys
DedupPeriodMinutes
The time period (in minutes) during which similar events of an alert will be grouped together
15,30,60,180 (3 hours),720 (12 hours), or 1440 (24 hours)
DisplayName
A user-friendly name to show in the Panther Console and alerts. The RuleID will be displayed if this field is not set.
String
OutputIds
Static destination overrides. These will be used to determine how alerts from this rule are routed, taking priority over default routing based on severity.
List of strings
Reference
The reason this rule exists, often a link to documentation
String
Reports
A mapping of framework or report names to values this rule covers for that framework
Map of strings to list of strings
Runbook
The actions to be carried out if this rule returns an alert, often a link to documentation
String
SummaryAttributes
A list of fields that alerts should summarize.
List of strings
Threshold
How many events need to trigger this rule before an alert will be sent.
Integer
Tags
Tags used to categorize this rule
List of strings
Tests
Unit tests for this rule
List of maps
InlineFilters
The list of filters in the form of match expressions to filter in data
List of match expressions (limited to filter-compatible versions)
An alternate DisplayName that can use event values to create a dynamic title for alerts
String
Event values to add to the Event under custom keys to create a dynamic alert context
List of key name and key value pairs