# Rules and Scheduled Rules

## **Overview**

Rules and scheduled rules are segments of logic through which log data is run to detect suspicious activity and generate alerts. Rules analyze real-time events, while scheduled rules analyze events queried from your data lake. These detection types differ from [policies](/~/changes/Dd8nx2iqd1Pp2OzWJaWk/detections/policies.md), which apply to cloud resource configurations. 

Rules can be created in the Console using the [Simple Detection builder](/~/changes/Dd8nx2iqd1Pp2OzWJaWk/detections/rules/simple-detection-builder.md) or by writing [Python](/~/changes/Dd8nx2iqd1Pp2OzWJaWk/detections/rules/python.md); in the CLI workflow, rules can be written in [Python](/~/changes/Dd8nx2iqd1Pp2OzWJaWk/detections/rules/python.md) or [YAML](/~/changes/Dd8nx2iqd1Pp2OzWJaWk/detections/rules/yaml.md). Scheduled rules can be written in [Python](/~/changes/Dd8nx2iqd1Pp2OzWJaWk/detections/rules/python.md) (in the Console or CLI workflow). Panther provides a number of [Panther-managed rules and scheduled rules](/~/changes/Dd8nx2iqd1Pp2OzWJaWk/detections/panther-managed.md) in Python, which are already written and continuously updated.

Common examples of rules include analyzing logs for:

* Authentication from unknown or unexpected locations
* Sensitive API calls, such as administrative changes to SaaS services
* Network traffic access to sensitive data sources, such as databases or virtual machines
* New, suspicious entries added into a system's scheduled tasks, like cron
* Alerts generated from NIDS, HIDS, or other security systems

### Rules vs. scheduled rules

Both rules and scheduled rules define logic through which log events are run—but rules analyze real-time events, while scheduled rules analyze events queried from your data lake.

* **Rules**
  * Rules, sometimes referred to as *real-time rules*, are the default mechanism of analyzing data sent to Panther. Rules work by accepting a defined set of log types such as one or more of the [Supported Logs sources](/~/changes/Dd8nx2iqd1Pp2OzWJaWk/data-onboarding/supported-logs.md), or your own [custom data](/~/changes/Dd8nx2iqd1Pp2OzWJaWk/data-onboarding/custom-log-types.md). Rules have the benefit of low-latency detection and alerting.
  * Use cases: High-signal logs that do not require joins with other data.
* **Scheduled rules**
  * Scheduled rules work by accepting individual rows output from an associated [Scheduled Search](/~/changes/Dd8nx2iqd1Pp2OzWJaWk/search/scheduled-searches.md).
  * Use cases: Searching windows of time further in the past, running statistical analysis over data, or joining separate data streams.

### Using Python vs. YAML

If you are writing rules locally, in the CLI workflow, you can use either Python or YAML. (Scheduled rules can only be written in Python.) There are advantages to using both languages, outlined below.

* Write rules in [Python](/~/changes/Dd8nx2iqd1Pp2OzWJaWk/detections/rules/python.md) when:
  * The complexity of the logic is very high, and cannot be represented in YAML.
  * The detection requires any of the features currently listed as [limitations of YAML](/~/changes/Dd8nx2iqd1Pp2OzWJaWk/detections/rules/yaml.md#limitations-of-yaml-detections).
* Write rules in [YAML](/~/changes/Dd8nx2iqd1Pp2OzWJaWk/detections/rules/yaml.md) when:
  * You'd like to promote collaboration between team members with differing levels of technical skill. When YAML detections are uploaded to Panther, they're represented in the Console in the [Simple Detection builder](/~/changes/Dd8nx2iqd1Pp2OzWJaWk/detections/rules/simple-detection-builder.md). You can then edit (or create new) detections in the Console using the Simple Detection builder.

For examples of the same detection logic written in both Python and YAML, see [Rule examples, below](#rule-examples).

## How rules and scheduled rules work

Rules and scheduled rules each analyze one event at a time. They use event thresholds and de-duplication to create event grouping within windows of time. 

At a minimum, each rule and scheduled rule must define rule logic. For [Python detections](/~/changes/Dd8nx2iqd1Pp2OzWJaWk/detections/rules/python.md), this means they each must contain a `rule()` function; for [YAML detections](/~/changes/Dd8nx2iqd1Pp2OzWJaWk/detections/rules/yaml.md), each must contain a `Detection` key with at least one [match expression](/~/changes/Dd8nx2iqd1Pp2OzWJaWk/detections/rules/yaml/match-expression.md).

`return True` triggers an alert, while `return False` does not trigger an alert.

Python rules can also define [dynamic alert functions](/~/changes/Dd8nx2iqd1Pp2OzWJaWk/detections/rules/python.md#alert-functions-in-python-detections), and YAML rules can use [dynamic alert keys](/~/changes/Dd8nx2iqd1Pp2OzWJaWk/detections/rules/yaml.md#dynamic-alert-keys-in-yaml-detections). Both can also utilize [Inline Filters](/~/changes/Dd8nx2iqd1Pp2OzWJaWk/detections/rules/inline-filters.md) that run before detection logic.

### Title of associated alerts

The title of an alert from a certain detection is determined by that detection's configuration. When a separate [deduplication string](#deduplication-of-alerts) is not explicitly set, the alert title is also used to deduplicate alerts.

#### How the alert title is set

The order of precedence for setting the alert title is as follows:

{% tabs %}
{% tab title="Python" %}

#### Alert title precedence in Python:

1. The output of the dynamic [`title()`](/~/changes/Dd8nx2iqd1Pp2OzWJaWk/detections/rules/python.md#title) function is used. 
2. If `title()` is not defined, the value of the detection's display name is used. This is defined:
   * In the Console: in the **Name** field
   * In the CLI workflow: in the `DisplayName` field in the YAML file
3. If there is no display name defined, the detection's ID is used. This is defined:
   * In the Console: in the **ID** field
   * In the CLI workflow: in the`RuleID` or `PolicyID` field in the YAML file
     {% endtab %}

{% tab title="YAML" %}

#### Alert title precedence in YAML:

1. The dynamic alert title is used. This is defined:
   * In the Console: in the **Optional Fields** > **Default title is** > **Change to** field
   * In the developer workflow: in the [`AlertTitle`](/~/changes/Dd8nx2iqd1Pp2OzWJaWk/detections/rules/yaml.md#alerttitle) field
2. If a dynamic alert title is not defined, the value of the detection's display name is used. This is defined:
   * In the Console: in the **Name** field
   * In the developer workflow: in the `DisplayName` field
3. If there is no display name defined, the detection's ID is used. This is defined:
   * In the Console: in the **ID** field
   * In the developer workflow: in the`RuleID` or `PolicyID` field 
     {% endtab %}
     {% endtabs %}

### Deduplication of alerts

Events triggering the same detection within its deduplication period that also share a deduplication string will be grouped together in a single alert. 

Each rule and scheduled rule has a default event threshold of `1` and deduplication period of `1h.` This means all events returning `True` from the `rule` function (with the same deduplication string) will be grouped into a single alert within the hour after first being generated. 

A rule or scheduled rule with an event threshold of `5` and deduplication period of `15m` would not trigger an alert until five or more events (with the same deduplication string) passed into the `rule` function returned `True` within a 15-minute time period.

#### Deduplication period

The detection editor in the Panther Console supports a maximum deduplication period of 24 hours. If you upload your detections via the bulk uploader or the [Panther Analysis Tool (PAT)](/~/changes/Dd8nx2iqd1Pp2OzWJaWk/panther-developer-workflows/ci-cd/deployment-workflows/pat.md), there is no limit on the value of `DedupPeriodMinutes`. 

The deduplication period is not affected by changing the status of an alert. This means, for example, events will continue to be grouped into the same alert for the length of the deduplication period *even* if an alert's status is changed to `Resolved`.

#### How the deduplication string is set

The order of precedence for setting the deduplication string is as follows:

{% tabs %}
{% tab title="Python" %}

#### Deduplication string precedence in Python:

1. The output of the dynamic [`dedup()`](/~/changes/Dd8nx2iqd1Pp2OzWJaWk/detections/rules/python.md#dedup) function is used. 
2. If`dedup()` is not defined, the alert title is used. The alert title is defined by [the order of precedence defined here](#alert-title-precedence-in-python).
   {% endtab %}

{% tab title="YAML" %}

#### Deduplication string precedence in YAML:

1. The value of the [`GroupBy`](/~/changes/Dd8nx2iqd1Pp2OzWJaWk/detections/rules/yaml.md#groupby) key is used. 
2. If `GroupBy` is not present, the alert title is used. The alert title is defined by [the order of precedence defined here](#alert-title-precedence-in-yaml).
   {% endtab %}
   {% endtabs %}

Which method you use to set the deduplication string depends on how granularly you want to group alerts:

* If you only want alerts generated by a certain detection to be grouped separately from alerts from *other* detections, using the detection's display name (given that the display name is unique) or ID as the deduplication string will suffice.
* If you want alerts generated by a certain detection to be grouped separately not only from alerts generated by *other* detections, but also from alerts triggered by the *same* detection where one or more event fields have different values, you can use [`title()`](/~/changes/Dd8nx2iqd1Pp2OzWJaWk/detections/rules/python.md#title) or  [`AlertTitle`](/~/changes/Dd8nx2iqd1Pp2OzWJaWk/detections/rules/yaml.md#alerttitle) (for Python and YAML detections, respectively) to dynamically set the alert title and therefore, the deduplication string.
* If you want to group alerts generated by a certain detection distinctly from alerts generated by the same detection where one or more event field values differ *and* you want to group the alerts based on one or more event fields that weren't used in `title()`  or `AlertTitle` (or if you didn't set `title()` or `AlertTitle` at all), you can use [`dedup()`](/~/changes/Dd8nx2iqd1Pp2OzWJaWk/detections/rules/python.md#dedup) or [`GroupBy`](/~/changes/Dd8nx2iqd1Pp2OzWJaWk/detections/rules/yaml.md#groupby) (for Python and YAML detections, respectively) to set the deduplication string.

## How to write rules and scheduled rules

You can write rules in the Panther Console (using the [Simple Detection builder](/~/changes/Dd8nx2iqd1Pp2OzWJaWk/detections/rules/simple-detection-builder.md) or Python) or locally (in YAML or Python); scheduled rules can be written in Python (in the Panther Console or locally).

Before you start writing a new rule, remember to check to see if there's an existing [Panther-managed rule](/~/changes/Dd8nx2iqd1Pp2OzWJaWk/detections/panther-managed.md) that meets your needs.

Writing detections locally means creating Python and/or YAML files that define a Panther detection on your own machine. After writing detections locally, you upload the files to your Panther instance, typically via [PAT](/~/changes/Dd8nx2iqd1Pp2OzWJaWk/panther-developer-workflows/ci-cd/deployment-workflows/pat.md).

Note: Anything printed to `stdout` or `stderr` by your Python code will end up in CloudWatch.  For SaaS/CPaaS customers, Panther engineers can see these CloudWatch logs during routine application monitoring.

### How to write rules

These instructions outline how to set up real-time rules. To configure a scheduled rule, see [How to write scheduled rules](#how-to-write-scheduled-rules).

Follow the below instructions to learn how to write rules:

* [In Python (in either the Console, or the CLI workflow)](/~/changes/Dd8nx2iqd1Pp2OzWJaWk/detections/rules/python.md#how-to-create-a-rule-in-python)
* [In the Simple Detection builder in the Console](/~/changes/Dd8nx2iqd1Pp2OzWJaWk/detections/rules/simple-detection-builder.md#how-to-create-a-rule-in-the-simple-detection-builder)
* [In YAML, in the CLI workflow](/~/changes/Dd8nx2iqd1Pp2OzWJaWk/detections/rules/yaml.md#how-to-create-a-rule-in-yaml)

### How to write scheduled rules

Scheduled rules are associated with one or more [Scheduled Searches](/~/changes/Dd8nx2iqd1Pp2OzWJaWk/search/scheduled-searches.md). If you have not yet created a scheduled search, follow the [How to create a Saved and Scheduled Search](/~/changes/Dd8nx2iqd1Pp2OzWJaWk/search/scheduled-searches.md#how-to-create-a-scheduled-search) instructions first, then return to these instructions to create the scheduled rule.

If the Scheduled Search returns multiple rows, each row is processed by the rule logic as a separate event. The number of alerts triggered depends on the deduplication settings you've configured on the scheduled rule. 

{% hint style="info" %}
We recommend doing as much data processing as is possible in SQL (i.e., in the [Scheduled Search](/~/changes/Dd8nx2iqd1Pp2OzWJaWk/search/scheduled-searches.md)) in order to take advantage of database optimizations and improve rule performance. 
{% endhint %}

Follow the below instructions to learn how to write scheduled rules:

* [In Python (in either the Console, or the CLI workflow)](/~/changes/Dd8nx2iqd1Pp2OzWJaWk/detections/rules/python.md#how-to-create-a-scheduled-rule-in-python)

## Rule errors and scheduled rule errors

Rule errors and scheduled rule errors are types of [detection errors](https://docs.panther.com/alerts#overview) generated when a detection's Python code raises an exception.

If there is no specific routing configured for rule errors, the alert for a rule error will route to the same [destination](https://docs.runpanther.io/destinations) used by the alert.  See [Routing order precedence on Alert Destinations](/~/changes/Dd8nx2iqd1Pp2OzWJaWk/alerts/destinations.md#routing-order-precedence) for more information.

In the event of a search timeout, the Python code for Destinations will not run. 

## Rule examples

See templates for rules and scheduled rules in the [panther-analysis GitHub repository](https://github.com/panther-labs/panther-analysis/tree/master/templates).

For in-depth information on how to write detections, see [Writing Python Detections](/~/changes/Dd8nx2iqd1Pp2OzWJaWk/detections/rules/python.md) and [Writing YAML Detections](/~/changes/Dd8nx2iqd1Pp2OzWJaWk/detections/rules/yaml.md).

### Auth0 multi-factor authentication policy disabled

See how one detection is represented in both Python and YAML:

{% tabs %}
{% tab title="Python" %}

#### Auth0 multi-factor authentication policy disabled detection in Python

View this detection in full [in the panther-analysis repository in GitHub](https://github.com/panther-labs/panther-analysis/blob/13e49e6589b1160928ec85678884da0e72e986f3/rules/auth0_rules/auth0_mfa_policy_disabled.py).

```python
from global_filter_auth0 import filter_include_event
from panther_auth0_helpers import auth0_alert_context, is_auth0_config_event
from panther_base_helpers import deep_get


def rule(event):
    if not filter_include_event(event):
        return False
    data_description = deep_get(event, "data", "description", default="<NO_DATA_DESCRIPTION_FOUND>")
    request_path = deep_get(
        event, "data", "details", "request", "path", default="<NO_REQUEST_PATH_FOUND>"
    )
    request_body = deep_get(event, "data", "details", "request", "body", default=[-1])
    return all(
        [
            data_description == "Set the Multi-factor Authentication policies",
            request_path == "/api/v2/guardian/policies",
            request_body == [],
            is_auth0_config_event(event),
        ]
    )
```

{% endtab %}

{% tab title="YAML" %}

#### Auth0 multi-factor authentication policy disabled detection in YAML

```yaml
Detection:
  - DeepKey:
      - data
      - description
    Condition: Equals
    Value: Set the Multi-factor Authentication policies
  - DeepKey:
      - data
      - details
      - request
      - path
    Condition: Equals
    Value: /api/v2/guardian/policies
  - DeepKey:
      - data
      - details
      - request
      - body
    Condition: IsNullOrEmpty
  - DeepKey:
      - data
      - details
      - request
      - channel
    Condition: Equals
    Value: 'https://manage.auth0.com/'
```

{% endtab %}
{% endtabs %}

### Detect and alert when an admin panel is accessed on a web server

As an example, let's write a rule to send an alert when an admin panel is accessed on a web server.&#x20;

Take the following NGINX log:

```javascript
{
  "httpReferer": "https://domain1.com/?p=1",
  "httpUserAgent": "Chrome/80.0.3987.132 Safari/537.36",
  "remoteAddr": "180.76.15.143",
  "request": "GET /admin-panel/ HTTP/1.1",
  "status": 200,
  "time": "2019-02-06 00:00:38 +0000 UTC"
}
```

We want to create a detection that:

* Looks for 200 (OK) web requests to any URL containing "admin-panel"
* Generates an an alert title that says there has been successful admin panel logins from a specific IP address
* Deduplicates events based on IP address

{% tabs %}
{% tab title="Python" %}

```python
def rule(event):
  return event.get('status') == 200 and 'admin-panel' in event.get('request')

    
def title(event):
  return f"Successful admin panel login detected from {event.get('remoteAddr')}"


def dedup(event):
  return event.get('remoteAddr')
```

{% endtab %}

{% tab title="YAML" %}

```yaml
Detection:
  - KeyPath: status
    Condition: Equals
    Value: 200
  - KeyPath: request
    Condition: Contains
    Value: 'admin-panel'

AlertTitle: "Successful admin panel login detected from {remoteAddr}"

GroupBy:
  - KeyPath: remoteAddr
```

{% endtab %}
{% endtabs %}

Then, the following would occur:

1. An alert would be generated and sent to the set of associated [destinations](/~/changes/Dd8nx2iqd1Pp2OzWJaWk/alerts/destinations.md), which by default are based on the rule severity.
2. The alert's title would say, "Successful admin panel login detected from 180.76.15.143".
3. Similar events with the same deduplication string of `180.76.15.143` would be appended to the same alert.
   * A unique alert will be generated for each unique deduplication string, which in this case, is the IP of the requestor.&#x20;
4. The recipient of the alert could then log into Panther to view all alert metadata and a summary of the events, as well as execute [searches](/~/changes/Dd8nx2iqd1Pp2OzWJaWk/search.md) across all events to perform additional analysis.

## Reference

### Alert severity

We recommend following these guidelines to define alert severity levels:

<table data-header-hidden><thead><tr><th width="150">Severity</th><th width="150">Exploitability</th><th width="206.00763358778624">Description</th><th>Examples</th></tr></thead><tbody><tr><td>Severity</td><td>Exploitability</td><td>Description</td><td>Examples</td></tr><tr><td><code>Info</code></td><td>None</td><td>No risk, simply informational</td><td>Gaining operational awareness.</td></tr><tr><td><code>Low</code></td><td>Difficult</td><td>Little to no risk if exploited</td><td>Non-sensitive information leaking such as system time and OS versions.</td></tr><tr><td><code>Medium</code></td><td>Difficult</td><td>Moderate risk if exploited</td><td>Expired credentials, missing protection against accidental data loss, encryption settings, best practice settings for audit tools.</td></tr><tr><td><code>High</code></td><td>Moderate</td><td>Very damaging if exploited</td><td>Large gaps in visibility, directly vulnerable infrastructure, misconfigurations directly related to data exposure.</td></tr><tr><td><code>Critical</code></td><td>Easy</td><td>Causes extreme damage if exploited</td><td>Public data/systems available, leaked access keys.</td></tr></tbody></table>


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