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4.2 Ensure a log metric filter and alarm exist for Management Console sign-in without Multi-Factor Authentication (MFA) (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 console logins that are not protected by MFA.

Rationale​

Monitoring for single-factor console logins will increase visibility into accounts that are not protected by MFA.

Audit​

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 in the output that 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 in the output 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": "{ ($.eventName = "ConsoleLogin") && ($.additionalEventData.MFAUsed != "Yes") }"

Or (To reduce false positives incase Single Sign-On (SSO) is used in organization):

"filterPattern": "{ ($.eventName = "ConsoleLogin") && ($.additionalEventData.MFAUsed != "Yes") && ($.userIdentity.type = "IAMUser") && ($.responseElements.ConsoleLogin = "Success") }"

  1. Note the <no_mfa_console_signin_metric> value associated with the filterPattern found in step 3.

  2. Get a list of CloudWatch alarms and filter on the <no_mfa_console_signin_metric> captured in step 4.

aws cloudwatch describe-alarms --query 'MetricAlarms[?MetricName== `<no_mfa_console_signin_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>"

Remediation​

Perform the following to setup the metric filter, alarm, Simple Notification Service (SNS) topic, and subscription:

  1. Create a metric filter based on filter pattern provided which checks for AWS Management Console sign-in without MFA, providing a <cloudtrail_log_group_name>.

Use Command:

aws logs put-metric-filter --log-group-name <cloudtrail_log_group_name> -- filter-name <no_mfa_console_signin_metric> --metric-transformations metricName= <no_mfa_console_signin_metric>,metricNamespace='cis_benchmark',metricValue=1 --filter-pattern '{ ($.eventName = "ConsoleLogin") && ($.additionalEventData.MFAUsed != "Yes") }'

Or (To reduce false positives if using Single Sign-On (SSO) in organization):

aws logs put-metric-filter --log-group-name <cloudtrail_log_group_name> -- filter-name <no_mfa_console_signin_metric> --metric-transformations metricName=<no_mfa_console_signin_metric>,metricNamespace='cis_benchmark',metricValue=1 --filter-pattern '{ ($.eventName = "ConsoleLogin") && ($.additionalEventData.MFAUsed != "Yes") && ($.userIdentity.type = "IAMUser") && ($.responseElements.ConsoleLogin = "Success") }'
note

You can choose your own metricName and metricNamespace strings. Use the same metricNamespace for all Foundations Benchmark metrics to group them together.

  1. Create an SNS topic that the alarm can notify:
aws sns create-topic --name <sns_topic_name>
note

You can execute this command once and then re-use the same topic for all monitoring alarms.

  1. 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>
note

You can execute this command once and then re-use the SNS subscription for all monitoring alarms.

  1. 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 <no_mfa_console_signin_alarm> --metric-name <no_mfa_console_signin_metric> --statistic Sum --period 300 --threshold 1 --comparison-operator GreaterThanOrEqualToThreshold --evaluation-periods 1 --namespace 'cis_benchmark' --alarm-actions <sns_topic_arn>

References​

CCE-79187-1
https://docs.aws.amazon.com/AmazonCloudWatch/latest/DeveloperGuide/viewing_metrics_with_cloudwatch.html
https://docs.aws.amazon.com/awscloudtrail/latest/userguide/receive-cloudtrail-log-files-from-multiple-regions.html
https://docs.aws.amazon.com/awscloudtrail/latest/userguide/cloudwatch-alarms-for-cloudtrail.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
  • Filter pattern set to { ($.eventName = "ConsoleLogin") && ($.additionalEventData.MFAUsed != "Yes") && ($.userIdentity.type = "IAMUser") && ($.responseElements.ConsoleLogin = "Success"} reduces false alarms raised when user logs in via SSO account.
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