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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 changes to S3 bucket policies.

Rationale​

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.

Monitoring changes to S3 bucket policies may reduce time to detect and correct permissive policies on sensitive S3 buckets.

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 CloudWatchLogsLogGroupArn note <cloudtrail_log_group_name>.

Example: for CloudWatchLogsLogGroupArn that looks like arn:aws:logs:<region>:<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 <trailname 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>:
aws logs describe-metric-filters --log-group-name "<cloudtrail_log_group_name>"
  1. Ensure the output from the above command contains the following:
"filterPattern": "{ ($.eventSource = s3.amazonaws.com) && (($.eventName = PutBucketAcl) || ($.eventName = PutBucketPolicy) || ($.eventName = PutBucketCors) || ($.eventName = PutBucketLifecycle) || ($.eventName = PutBucketReplication) || ($.eventName = DeleteBucketPolicy) || ($.eventName = DeleteBucketCors) || ($.eventName = DeleteBucketLifecycle) || ($.eventName = DeleteBucketReplication)) }"
  1. Note the <s3_bucket_policy_changes_metric> value associated with the filterPattern found in step 3.
  2. Get a list of CloudWatch alarms and filter on the <s3_bucket_policy_changes_metric> captured in step 4:
aws cloudwatch describe-alarms --query 'MetricAlarms[?MetricName== `<s3_bucket_policy_changes_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. CCE-79193-9
  2. https://docs.aws.amazon.com/awscloudtrail/latest/userguide/cloudwatch-alarms-for-cloudtrail.html
  3. https://docs.aws.amazon.com/awscloudtrail/latest/userguide/receive-cloudtrail-log-files-from-multiple-regions.html
  4. 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.