lacework-global-62
Ensure a log metric filter and alarm exist for S3 bucket policy changes (Automated)
Profile Applicability
• Level 1
Description
Achieve real-time monitoring of API calls by directing CloudTrail Logs to CloudWatch Logs and establishing corresponding metric filters and alarms. Best practices recommend using a metric filter and alarm for changes to S3 bucket policies.
Rationale
Monitoring changes to S3 bucket policies may reduce time to detect and correct permissive policies on sensitive S3 buckets.
Audit
Perform the following to ensure that there is at least one active multi-region CloudTrail with prescribed metric filters and alarms configured:
- 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
- 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>"
- 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)) }"
Note the
<s3_bucket_policy_changes_metric>
value associated with thefilterPattern
found in step 3.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>`]'
Note the
AlarmActions
value - this will provide the SNS topic ARN value.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>"
Remediation
Perform the following to setup the metric filter, alarm, Simple Notification Service (SNS) topic, and subscription:
- Create a metric filter based on filter pattern provided which checks for S3 bucket policy changes, providing a
<cloudtrail_log_group_name>
.
aws logs put-metric-filter --log-group-name <cloudtrail_log_group_name> --filter-name <s3_bucket_policy_changes_metric> --metric-transformations metricName=<s3_bucket_policy_changes_metric>,metricNamespace='cis_benchmark',metricValue=1 \
--filter-pattern '{ ($.eventSource = s3.amazonaws.com) && (($.eventName = PutBucketAcl) || ($.eventName = PutBucketPolicy) || ($.eventName = PutBucketCors) || ($.eventName = PutBucketLifecycle) || ($.eventName = PutBucketReplication) || ($.eventName = DeleteBucketPolicy) || ($.eventName = DeleteBucketCors) || ($.eventName = DeleteBucketLifecycle) || ($.eventName = DeleteBucketReplication)) }'
You can choose your own metricName and metricNamespace strings. Use the same metricNamespace for all Foundations Benchmark metrics to group them together.
- Create an SNS topic that the alarm can notify:
aws sns create-topic --name <sns_topic_name>
You can execute this command once and then re-use the same topic for all monitoring alarms.
- Create an SNS subscription to the topic created in step 2:
aws sns subscribe --topic-arn <sns_topic_arn> --protocol <protocol_for_sns> --notification-endpoint <sns_subscription_endpoints>
You can execute this command once and then re-use the SNS subscription for all monitoring alarms.
- Create an alarm associated with the CloudWatch Logs Metric Filter created in step 1 and an SNS topic created in step 2:
aws cloudwatch put-metric-alarm --alarm-name <s3_bucket_policy_changes_alarm> --metric-name <s3_bucket_policy_changes_metric> --statistic Sum --period 300 --threshold 1 --comparison-operator GreaterThanOrEqualToThreshold --evaluation-periods 1 --namespace 'cis_benchmark' --alarm-actions <sns_topic_arn>
References
CCE-79193-9
https://docs.aws.amazon.com/awscloudtrail/latest/userguide/cloudwatch-alarms-for-cloudtrail.html
https://docs.aws.amazon.com/awscloudtrail/latest/userguide/receive-cloudtrail-log-files-from-multiple-regions.html
https://docs.aws.amazon.com/sns/latest/dg/SubscribeTopic.html
Additional Information
Configuring log metric filter and alarm on Multi-region (global) CloudTrail:
- ensures monitoring of activities from all regions (used as well as unused)
- ensures monitoring of activities on all supported global services
- ensures monitoring of all management events across all regions