Policies
Scan and evaluate cloud infrastructure configurations
Overview
Policies are Python functions used to identify misconfigured cloud infrastructure and generate alerts for your team. Panther provides a number of already written and continuously updated Panther-managed policies.
How to write a policy
Before you start writing a new policy, remember to check to see if there's an existing Panther-managed policy that meets your needs.
Policy Body
The policy body must:
Be valid Python3.
Define a
policy()
function that accepts oneresource
argument.Each policy takes a
resource
input of a given resource type from the supported resources page.
Return a
bool
from the policy function.
def policy(resource):
return True
The Python body should name the argument to the policy()
function resource
and also may do the following:
Import standard Python3 libraries
Import from the user defined
aws_globals
moduleImport from the Panther defined
panther
moduleDefine additional helper functions as needed
Define variables and classes outside the scope of the rule function
Using the schemas in supported resources provides details on all available fields in resources. Top level keys are always present, although they may contain NoneType
values.
Writing policies locally and in the Panther Console
You can write and deploy policies in the Panther Console or you can write them locally and upload them to Panther via Panther Analysis Tool (PAT). For detailed instructions on configuring PAT, see Panther Developer Workflows.
How to write policies in the Panther Console
In the left-hand navigation bar of your Panther Console, click Build > Detections.
In the upper-right corner, click Create New.
At the top of the page, choose Policy as the detection type.
In the Basic Info section, provide values for the following fields:
Name: Enter a descriptive name for the policy.
ID (optional): Click the pen icon and enter a unique ID for your policy.
In the upper-right corner, click Continue.
On the next page, configure your policy:
In the upper-right corner, the Enabled toggle will be set to
ON
by default. If you'd like to disable the policy, flip the toggle toOFF
.In the For the Following Resource Types section:
Resource Types: Select one or more resource types this policy should apply to. Leave empty to apply to all resources.
In the Detect section:
In the Policy Function text editor, write a Python
policy
function to define your detection.For detection templates and examples, see the panther_analysis GitHub repository
In the Set Alert Fields section:
Severity: Select a severity level for the alerts triggered by this detection.
In the Optional Fields section, optionally provide values for the following fields:
Description: Enter additional context about the policy.
Runbook: Enter the procedures and operations relating to this policy.
To see examples of runbooks for built-in rules, see Alert Runbooks.
Reference: Enter an external link to more information relating to this rule.
Destination Overrides: Choose destinations to receive alerts for this detection, regardless of severity. Note that destinations can also be set dynamically, in the rule function. See Routing Order Precedence to learn more about routing precedence.
Ignore Patterns: Enter patterns to ignore.
Custom Tags: Enter custom tags to help you understand the rule at a glance (e.g.,
HIPAA
.)In the Framework Mapping section:
Click Add New to enter a report.
Provide values for the following fields:
Report Key: Enter a key relevant to your report.
Report Values: Enter values for that report.
In the Test section:
In the Unit Test section, click Add New to create a test for the policy you defined in the previous step.
In the upper-right corner, click Save.
Policy Writing Best Practices
Constructing Test Resources
Manually building test cases can be prone to human error. We suggest one of the following methods:
Option 1: In the Panther Console, navigate to Investigate > Cloud Resources. Apply a filter of the resource type you intend to emulate in your test. Select a resource in your environment, and on the
Attributes
card you can copy the full JSON representation of that resource by selecting copy button next to the wordroot
.Option 2: Open the Panther Resources documentation, and navigate to the section for the resource you are trying to emulate. Copy the provided example resource. Paste this in to the resource editor if you're working in the web UI, or into the
Resource
field if you are working locally. Now you can manually modify the fields relevant to your policy and the specific test case you are trying to emulate.
Option 1 is best when it is practical, as this can provide real test data for your policies. Additionally, it is often the case that you are writing/modifying a policy specifically because of an offending resource in your account. Using that exact resource's JSON representation as your test case can guarantee that similar resources will be caught by your policy in the future.
Debugging Exceptions
Debugging exceptions can be difficult, as you do not have direct access to the Python environment running the policies.
When you see a policy that is showing the state Error
on a given resource, that means that the policy threw an exception. The best method for troubleshooting these errors is to use option 1 in the Constructing test resources section above and create a test case from the resource causing the exception.
Running this test case either locally or in the Panther Console should provide more context for the issue, and allow you to modify the policy to debug the exception without having to run the policy against all resources in your environment.
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.
Policy examples
S3 public read access
In the example below, the policy checks if an S3 bucket allows public read access:
# A list of grantees that represent public access
GRANTEES = {
'http://acs.amazonaws.com/groups/global/AuthenticatedUsers',
'http://acs.amazonaws.com/groups/global/AllUsers'
}
PERMISSIONS = {'READ'}
def policy(resource):
for grant in resource['Grants']:
if grant['Grantee']['URI'] in GRANTEES and grant[
'Permission'] in PERMISSIONS:
return False
return True
IAM Password Policy
This example policy alerts when the password policy does not enforce a maximum password age:
def policy(resource):
if resource['MaxPasswordAge'] is None:
return False
return resource['MaxPasswordAge'] <= 90
In the policy()
body, returning a value of True
indicates the resource is compliant and no alert should be sent. Returning a value of False
indicates the resource is non-compliant.
The policy is based on an IAM Password Policy resource:
{
"AccountId": "123456789012",
"AllowUsersToChangePassword": true,
"AnyExist": true,
"ExpirePasswords": true,
"HardExpiry": null,
"MaxPasswordAge": 90,
"MinimumPasswordLength": 14,
"Name": "AWS.PasswordPolicy",
"PasswordReusePrevention": 24,
"Region": "global",
"RequireLowercaseCharacters": true,
"RequireNumbers": true,
"RequireSymbols": true,
"RequireUppercaseCharacters": true,
"ResourceId": "123456789012::AWS.PasswordPolicy",
"ResourceType": "AWS.PasswordPolicy",
"Tags": null,
"TimeCreated": null
}
Policy Specification Reference
Required fields are in bold.
A complete list of policy specification fields:
Field Name
Description
Expected Value
AnalysisType
Indicates whether this specification is defining a policy or a rule
policy
Enabled
Whether this policy is enabled
Boolean
FileName
The path (with file extension) to the python policy body
String
PolicyID
The unique identifier of the policy
String
ResourceTypes
What resource types this policy will apply to
List of strings
Severity
What severity this policy is
One of the following strings: Info
, Low
, Medium
, High
, or Critical
Description
A brief description of the policy
String
DisplayName
What name to display in the UI and alerts. The PolicyID
will be displayed if this field is not set.
String
Reference
The reason this policy exists, often a link to documentation
String
Reports
A mapping of framework or report names to values this policy covers for that framework
Map of strings to list of strings
Runbook
The actions to be carried out if this policy fails, often a link to documentation
String
Tags
Tags used to categorize this policy
List of strings
Tests
Unit tests for this policy.
List of maps
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