[Rule Tuning] Add Investigation Guides to AWS Rules

rules/integrations/aws/discovery_ec2_multi_region_describe_instances.toml

@@ -12,10 +12,61 @@ window. This could indicate a potential threat actor attempting to discover the
 regions using compromised credentials or a compromised instance. Adversaries may use this information to identify
 potential targets for further exploitation or to gain a better understanding of the target's infrastructure.
 """
+false_positives = [
+    """
+    Legitimate use of the `DescribeInstances` API call by an AWS resource that requires information about instances in
+    multiple regions.
+    """,
+    "Scheduled tasks or scripts that require information about instances in multiple regions.",
+]
 from = "now-9m"
 language = "esql"
 license = "Elastic License v2"
 name = "AWS EC2 Multi-Region DescribeInstances API Calls"
+note = """## Triage and Analysis
+
+### Investigating AWS EC2 Multi-Region DescribeInstances API Calls
+
+This rule detects instances where a single AWS resource makes `DescribeInstances` API calls in over 10 regions within a 30-second window. This could indicate an adversary using compromised credentials or an exploited resource to enumerate AWS infrastructure across multiple regions. Attackers often leverage multi-region enumeration to assess the overall cloud environment and find potential targets for further exploitation.
+
+#### Possible Investigation Steps
+
+- **Identify the Resource and Actor**:
+  - **Actor ARN**: Check `aws.cloudtrail.user_identity.arn` to determine the exact identity performing the enumeration. Validate if the user is expected to perform region-wide `DescribeInstances` actions across multiple regions or if it seems unusual.
+  - **Account and Role Details**: Examine `cloud.account.id` and `aws.cloudtrail.user_identity.session_context.session_issuer` for information about the AWS account and specific role associated with the action.
+
+- **Analyze API Call Patterns**:
+  - **Frequency and Scope**: Review `cloud.region` field and confirm if this specific resource commonly performs `DescribeInstances` calls across multiple regions.
+  - **Time Window Context**: Compare the timing of the API calls within the `target_time_window` to determine if this burst pattern aligns with expected system usage or is potentially malicious.
+
+- **Check User Agent and Tooling**:
+  - **Source and User Agent**: Verify `user_agent.original` to determine if the request was made through expected tooling (e.g., AWS CLI or SDK) or a third-party tool that might indicate non-standard access.
+  - **Source IP Address**: Look into `source.address` to identify the origin of the calls. Unusual IP addresses, especially those outside expected ranges, may indicate compromised access.
+
+- **Evaluate for Potential Reconnaissance Behavior**:
+  - **Account and Region Enumeration**: Adversaries may use region-wide `DescribeInstances` requests to discover resources within an account across different regions. Confirm if this access aligns with operational practices or represents excessive access.
+  - **Permissions and Roles**: Investigate the permissions associated with the user role. Excessive permissions on a compromised role may allow broader enumeration, which should be restricted.
+
+- **Review Related CloudTrail Events**:
+  - **Additional Describe or List Actions**: Identify any associated `Describe` or `List` API calls that may indicate further enumeration of other AWS services within the same timeframe.
+  - **Potential Preceding Events**: Look for preceding login or access events from the same actor, as these may indicate potential credential compromise or unauthorized escalation of privileges.
+
+### False Positive Analysis
+
+- **Expected Enumeration**: Certain administrative or automation scripts may conduct broad `DescribeInstances` API calls for inventory purposes. Review usage patterns or consult relevant teams to validate the purpose.
+- **Automated Cloud Management**: Some automated services may perform regional checks for compliance or backup operations. If this rule is triggered repeatedly by a known service, consider whitelisting or tuning accordingly.
+
+### Response and Remediation
+
+- **Review IAM Policies and Role Permissions**: Limit the permissions of roles associated with this resource, restricting unnecessary multi-region enumeration access.
+- **Enforce Least Privilege Access**: Ensure that permissions for DescribeInstances are tightly controlled and restricted to specific roles or accounts that require multi-region access.
+- **Increase Monitoring and Alerts**: Set up additional monitoring on this role or account for further signs of unauthorized activity or lateral movement attempts.
+- **Access Review**: Conduct a review of users and entities with `DescribeInstances` permissions, especially for multi-region capabilities, and ensure these permissions are necessary for their functions.
+
+### Additional Information
+
+For further information on AWS `DescribeInstances` permissions and best practices, refer to the [AWS DescribeInstances API documentation](https://docs.aws.amazon.com/AWSEC2/latest/APIReference/API_DescribeInstances.html).
+"""
 references = [
     "https://www.sentinelone.com/labs/exploring-fbot-python-based-malware-targeting-cloud-and-payment-services/",
     "https://docs.aws.amazon.com/AWSEC2/latest/APIReference/API_DescribeInstances.html",
@@ -27,6 +78,7 @@ tags = [
     "Domain: Cloud",
     "Data Source: AWS",
     "Data Source: AWS EC2",
+    "Resources: Investigation Guide",
     "Use Case: Threat Detection",
     "Tactic: Discovery",
 ]

rules/integrations/aws/execution_ssm_sendcommand_by_rare_user.toml

@@ -0,0 +1,123 @@
+[metadata]
+creation_date = "2020/07/06"
+integration = ["aws"]
+maturity = "production"
+updated_date = "2024/11/05"
+
+[rule]
+author = ["Elastic"]
+description = """
+Detects the execution of commands or scripts on EC2 instances using AWS Systems Manager (SSM), such as `RunShellScript`,
+`RunPowerShellScript` or custom documents. While legitimate users may employ these commands for management tasks, they
+can also be exploited by attackers with credentials to establish persistence, install malware, or execute reverse shells
+for further access to compromised instances. This is a [New
+Terms](https://www.elastic.co/guide/en/security/current/rules-ui-create.html#create-new-terms-rule) rule that looks for
+the first instance of this behavior by the `aws.cloudtrail.user_identity.arn` field in the last 7 days.
+"""
+false_positives = [
+    """
+    Verify whether the user identity, user agent, and/or hostname should be making changes in your environment.
+    Suspicious commands from unfamiliar users or hosts should be investigated. If known behavior is causing false
+    positives, it can be exempted from the rule.
+    """,
+]
+from = "now-9m"
+index = ["filebeat-*", "logs-aws.cloudtrail-*"]
+language = "kuery"
+license = "Elastic License v2"
+name = "AWS SSM `SendCommand` Execution by Rare User"
+note = """## Triage and Analysis
+
+### Investigating AWS SSM `SendCommand` Execution by Rare User
+
+This rule detects the execution of commands or scripts on EC2 instances using AWS Systems Manager (SSM) by an unexpected or new user. The SSM `SendCommand` action can enable remote command execution, which adversaries may exploit to install backdoors, deploy malware, or interact with compromised instances through reverse shells.
+
+#### Possible Investigation Steps
+
+- **Identify the Target Instance**:
+  - **Instance ID**: Review the `aws.cloudtrail.flattened.request_parameters.targets` field to identify which EC2 instances were targeted by this command. Confirm if these instances are expected to be managed through SSM.
+  - **Document Used**: Check the `aws.cloudtrail.flattened.request_parameters.documentName` field, which specifies the document or script being executed. Commands such as `RunShellScript` or `RunPowerShellScript` can indicate interactive sessions or script-based interactions.
+
+- **Review User Context**:
+  - **User Identity**: Inspect the `aws.cloudtrail.user_identity.arn` field to determine the user or role executing the `SendCommand`. If this user is not typically involved in EC2 or SSM interactions, this could indicate unauthorized access.
+  - **Access Patterns**: Validate whether the user typically has permissions to perform `SendCommand` operations on instances and whether the frequency of this action matches expected behavior.
+
+- **Analyze Command Parameters**:
+  - **Document Contents**: While the exact command may not be visible in CloudTrail, use logs to determine the purpose of the script, especially if the document name suggests encryption, data transfer, or reverse shell capabilities.
+  - **Timing and Context**: Compare this command execution with other recent SSM actions in your environment. A single `SendCommand` event by an unusual user can indicate an early stage of a larger attack.
+
+- **Check User Agent and Source IP**:
+  - **User Agent Analysis**: Review the `user_agent.original` field to verify the tool or client used (e.g., `aws-cli`). This can provide insight into whether this action was automated, scripted, or executed manually.
+  - **Source IP and Geolocation**: Use `source.address` and `source.geo` fields to check if the IP address and geolocation align with expected regions for your organization. Unusual IP addresses or locations can indicate external adversaries.
+
+- **Evaluate for Persistence Indicators**:
+  - **Command Consistency**: Investigate if this action is part of a recurring pattern, such as repeated command executions across instances, which may suggest an attempt to maintain access.
+  - **Permissions**: Ensure that the IAM policies associated with the user limit `SendCommand` actions to necessary use cases. Consider adding alerts for commands executed by users with minimal roles or permissions.
+
+- **Correlate with Other CloudTrail Events**:
+  - **Cross-Reference SSM Actions**: Look for other recent SSM actions like `CreateDocument`, `UpdateDocument`, or additional `SendCommand` events that could indicate preparation for further exploitation.
+  - **Monitor Data Access or Modification**: Correlate with `S3` access patterns, IAM changes, or EC2 modifications in recent events to detect broader malicious activities.
+
+### False Positive Analysis
+
+- **Routine Automation**: SSM `SendCommand` may be used by automation scripts or management tools. Verify if this event aligns with known, routine automated workflows.
+- **Maintenance Activity**: Confirm if legitimate administrative activities, such as patching or updates, are expected at this time, which may involve similar commands executed on multiple instances.
+
+### Response and Remediation
+
+- **Limit SSM Permissions**: If unauthorized, immediately revoke `SendCommand` permissions from the user or role to prevent further access.
+- **Quarantine Target Instance**: If malicious behavior is confirmed, isolate the affected EC2 instance(s) to limit lateral movement or data exfiltration.
+- **Investigate and Contain User Account**: If the action was performed by a compromised account, review recent activity and reset access credentials as necessary.
+- **Audit SSM and IAM Configurations**: Periodically review permissions associated with SSM usage and ensure least privilege access principles are in place.
+
+### Additional Information
+
+For further details on managing AWS SSM and security best practices for EC2 instances, refer to the [AWS Systems Manager Documentation](https://docs.aws.amazon.com/systems-manager/latest/userguide/ssm-plugins.html) and AWS best practices.
+"""
+references = ["https://docs.aws.amazon.com/systems-manager/latest/userguide/ssm-plugins.html"]
+risk_score = 21
+rule_id = "37b211e8-4e2f-440f-86d8-06cc8f158cfa"
+severity = "low"
+tags = [
+    "Domain: Cloud",
+    "Data Source: AWS",
+    "Data Source: Amazon Web Services",
+    "Data Source: AWS SSM",
+    "Use Case: Log Auditing",
+    "Use Case: Threat Detection",
+    "Tactic: Execution",
+    "Resources: Investigation Guide",
+]
+timestamp_override = "event.ingested"
+type = "new_terms"
+
+query = '''
+event.dataset: "aws.cloudtrail"
+    and event.provider: "ssm.amazonaws.com"
+    and event.action: "SendCommand"
+    and event.outcome: "success"
+    and not aws.cloudtrail.user_identity.arn: *AWSServiceRoleForAmazonSSM/StateManagerService*
+'''
+
+
+[[rule.threat]]
+framework = "MITRE ATT&CK"
+[[rule.threat.technique]]
+id = "T1651"
+name = "Cloud Administration Command"
+reference = "https://attack.mitre.org/techniques/T1651/"
+
+
+[rule.threat.tactic]
+id = "TA0002"
+name = "Execution"
+reference = "https://attack.mitre.org/tactics/TA0002/"
+
+[rule.new_terms]
+field = "new_terms_fields"
+value = ["aws.cloudtrail.user_identity.arn"]
+[[rule.new_terms.history_window_start]]
+field = "history_window_start"
+value = "now-7d"
+
+