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Description

Real-time monitoring of API calls can be achieved by directing CloudTrail Logs to CloudWatch Logs, or an external Security information and event management (SIEM) environment, and establishing corresponding metric filters and alarms.

It is recommended that a metric filter and alarm be established for unauthorized API calls.

Rationale​

Monitoring unauthorized API calls will help reduce time to detect malicious activity and can alert you to a potential security incident.

CloudWatch is an AWS native service that allows you to observe and monitor resources and applications. CloudTrail Logs can also be sent to an external Security information and event management (SIEM) environment for monitoring and alerting.

Impact​

This alert may be triggered by normal read-only console activities that attempt to opportunistically gather optional information, but gracefully fail if they don't have permissions.

If an excessive number of alerts are being generated then an organization may wish to consider adding read access to the limited IAM user permissions simply to quiet the alerts.

In some cases doing this may allow the users to actually view some areas of the system - any additional access given should be reviewed for alignment with the original limited IAM user intent.

Audit​

If you are using CloudTrails and CloudWatch, perform the following to ensure that there is at least one active multi-region CloudTrail with prescribed metric filters and alarms configured:

  1. Identify the log group name configured for use with active multi-region CloudTrail:
  • List all CloudTrails:
aws cloudtrail describe-trails
  • Identify Multi region Cloudtrails: Trails with IsMultiRegionTrail set to true.
  • From value associated with Name note <cloudtrail__name>.
  • From value associated with CloudWatchLogsLogGroupArn note <cloudtrail_log_group_name>.

Example: for CloudWatchLogsLogGroupArn that looks like arn:aws:logs::<aws_account_number>:log-group:NewGroup:*, <cloudtrail_log_group_name> would be NewGroup.

  • Ensure Identified Multi region CloudTrail is active:
aws cloudtrail get-trail-status --name <Name of a Multi-region CloudTrail>

Ensure IsLogging is set to TRUE.

  • Ensure identified Multi-region Cloudtrail captures all Management Events:
aws cloudtrail get-event-selectors --trail-name "<Name as shown in describe-trails>"

Ensure there is at least one Event Selector for a Trail with IncludeManagementEvents set to true and ReadWriteType set to All.

  1. Get a list of all associated metric filters for this <cloudtrail_log_group_name> that you captured in step 1:
aws logs describe-metric-filters --log-group-name "<cloudtrail_log_group_name>"
  1. Ensure the output from the above command contains the following:
"filterPattern": "{ ($.errorCode ="*UnauthorizedOperation") || ($.errorCode ="AccessDenied*") && ($.sourceIPAddress!="delivery.logs.amazonaws.com") && ($.eventName!="HeadBucket") }",
  1. Note the filterName <unauthorized_api_calls_metric> value associated with the filterPattern found in step 3.
  2. Get a list of CloudWatch alarms and filter on the <unauthorized_api_calls_metric> captured in step 4:
aws cloudwatch describe-alarms --query "MetricAlarms[?MetricName == `<unauthorized_api_calls_metric>`]"
  1. Note the AlarmActions value - this will provide the SNS topic ARN value.
  2. Ensure there is at least one active subscriber to the SNS topic:
aws sns list-subscriptions-by-topic --topic-arn <sns_topic_arn>

At least one subscription should have SubscriptionArn with valid aws ARN.

Example of valid SubscriptionArn: "arn:aws:sns:<region>:<aws_account_number>:<SnsTopicName>:<SubscriptionID>".

References​

  1. https://aws.amazon.com/sns/
  2. CCE-79186-3
  3. https://docs.aws.amazon.com/awscloudtrail/latest/userguide/receive-cloudtrail-log-files-from-multiple-regions.html
  4. https://docs.aws.amazon.com/awscloudtrail/latest/userguide/cloudwatch-alarms-for-cloudtrail.html
  5. https://docs.aws.amazon.com/sns/latest/dg/SubscribeTopic.html

Additional Information​

Configuring log metric filter and alarm on Multi-region (global) CloudTrail:

  • Ensures that activities from all regions (used as well as unused) are monitored.
  • Ensures that activities on all supported global services are monitored.
  • Ensures that all management events across all regions are monitored.