Automatically resolve Security Hub findings for resources that no longer exist
In this post, you’ll learn how to automatically resolve AWS Security Hub findings for previously deleted Amazon Web Services (AWS) resources. By using an event-driven solution, you can automatically resolve findings for AWS and third-party service integrations.
Security Hub provides a comprehensive view of your security alerts and security posture across your AWS accounts. Security Hub provides a single place that aggregates, organizes, and prioritizes your security alerts (also called findings) from multiple AWS services and partner solutions. Security Hub lets you assign workflow statuses of NEW, NOTIFIED, SUPPRESSED, or RESOLVED to findings. These statuses help you understand the state of your security findings and identify which need attention. As AWS resources are spun up and down during the course of normal business activities, there might be findings in Security Hub for those resources. AWS Security Hub findings backed by AWS Config are automatically archived when AWS Config identifies that a resource has been deleted. However, for some AWS service integrations—such as Amazon GuardDuty and third-party partner products—findings aren’t automatically resolved or archived when a resource is deleted. This can result in orphaned findings for resources that no longer exist.
In this post, we show you how to use an event-driven architecture to automatically resolve findings for all providers—AWS and third-party—for resources that have been deleted. Automatically resolving these findings reduces alert fatigue by decreasing noise, allowing your security team to focus on investigating and remediating high fidelity findings.
A common use case for automatically resolving findings is for Amazon Elastic Compute Cloud (Amazon EC2) instances that are ephemeral in nature. For example, Amazon EC2 instances that are part of an Amazon EC2 Auto Scaling group. EC2 instances can scale to thousands of nodes multiple times a day depending on the workload. Without automatically resolving these findings, you could end up with one or more findings for each instance. By automatically resolving findings for the deleted resources, your teams can focus on investigating and remediating findings that affect active resources.
This solution assumes that you have Security Hub and AWS Config configured across all of your AWS accounts. Instructions for configuring Security Hub and its dependencies can be found in the Security Hub user guide. Ensure you have configured Security Hub to use a delegated administrator account, which centralizes findings from all member accounts.
In Security Hub, the investigation status of a finding is tracked using the workflow status attribute. The workflow status attribute for new findings is initially set to NEW. You can change the workflow status of a finding by either selecting it in the AWS Security Hub console, or by automating the change of workflow status by using the AWS Command Line Interface (AWS CLI) or Security Hub SDKs. The usual workflow for a finding, whether managed manually or through automation, is NEW, NOTIFIED, then RESOLVED or SUPPRESSED.
In this solution, we show you how to automatically set the workflow status to RESOLVED for all applicable findings when an EC2 instance, Amazon Simple Storage Service (Amazon S3) bucket, or an AWS Identity and Access Management (IAM) role is deleted. This event-driven solution uses Amazon EventBridge event patterns—which can be easily customized to meet your specific business needs—to invoke the resolution workflow on Delete or Terminate API calls. An EventBridge event bus is used to forward all Delete or Terminate API calls to your Security Hub delegated administrator account. Event patterns are used to filter for specific events and forward them to a target. With this solution, you filter for specific Delete and Terminate events, identified by the event name. The target for matching events is an AWS Lambda function. The invocation of this function includes context around the event which includes the metadata for the resource that was just deleted or terminated. This function queries the Security Hub GetFindings API for all findings for the resource with a status of NEW or NOTIFIED. The function then sets the workflow status to RESOLVED for all findings for the Amazon Resource Name (ARN) of the given resource by calling the BatchUpdateFindings Security Hub API.
Figure 1 shows the deletion of an AWS resource in a Security Hub member account being forwarded to the EventBridge event bus in the Security Hub administrator account. The process flow is as follows:
- In a Security Hub member account, a user deletes or terminates a resource through the AWS Management Console, AWS CLI, or SDK.
- AWS CloudTrail logs the user activity and automatically forwards an event to EventBridge.
- An EventBridge event pattern filters for the delete or terminate API call, and generates an event.
- The event is forwarded to the event bus in the Security Hub administrator account.
- In the Security Hub administrator account, an event pattern is used to filter for all delete or terminate API calls.
- Matching events generate an EventBridge event.
- The target for this event is the Lambda function to resolve Security Hub findings for the recently deleted resource.
- The Lambda function generates a list of all findings for the recently deleted resource and updates the workflow status for each finding to RESOLVED in the Security Hub delegated administrator account.
- The workflow status propagates from the Security Hub delegated administrator account to the member accounts of Security Hub.
To deploy the solution
In the Security Hub administrator account complete the following steps:
- In the following resource policy, replace <Region> with the AWS Region where the solution is deployed, <AccountID> with the Security Hub administrator account ID and <OrgID> is the ID of the organization within your AWS Organizations implementation.
- Add the edited resource policy to the default EventBridge event bus to allow all accounts in your organization to send delete events for IAM roles, EC2 instances, and S3 buckets to the default event bus in the Security Hub administrator account.
Note: You can also choose to specify a list of accounts to receive events from. For more information about configuring a resource policy see Managing event bus permissions in Permissions for Amazon EventBridge event buses.
- Deploy the AWS CloudFormation template that creates the required resources.
In each Security Hub member account, deploy the CloudFormation template. You will need to specify the Security Hub administrator AWS account ID to deploy the stack.
Tip: CloudFormation StackSets can be used to deploy stacks across all accounts in your organization. For more information, see Working with AWS CloudFormation StackSets.
Note: With CloudFormation StackSets, the template isn’t deployed in the StackSet administrator account by default. The CloudFormation stack must be deployed separately in the StackSet administrator account.
Note: Security Hub now supports cross-Region aggregation of findings. If you have Security Hub cross-Region aggregation enabled. The solution in this post will work for findings in all aggregated regions.
Understanding and fixing the root cause for Security Hub findings will improve your security posture and reduce the number of future findings. As a best practice, you should periodically analyze the findings for resources that have been automatically resolved by this solution to identify trends so that your team can investigate and fix root causes. You can use the filter below in the Security Hub console to view all findings automatically resolved by this solution:
To analyze findings
- Open the Security Hub console and select Findings.
- Check to see that Workflow status is RESOLVED and Note updated by is DeletedResourceFindingResolver.
- (Optional) You can also create a custom insight for these findings by adding Group by: ProductName to the filter.
- Select Create Insight as shown in Figure 2.
Note: You can expand the solution to include other resource types based on your requirements, such as security groups, Amazon Relational Database Service (Amazon RDS) databases, and IAM users by updating the event pattern in the EventBridge rule and modifying the Lambda function code.
In this post, we showed how you can automatically resolve findings for deleted EC2, IAM and S3 resources by using the Security Hub GetFindings and BatchUpdateFindings API actions. We showed you how to configure EventBridge patterns and rules to initiate a Lambda function through a centralized event bus to address these findings for resources across your Organizations.
If you have feedback about this post, submit comments in the Comments section below. If you have questions about this post, start a new thread on the Security Hub forum. To start your 30-day free trial of Security Hub, visit AWS Security Hub.
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