CloudWatch S3 policy Change Alarm Missing

• Query id: 27c6a499-895a-4dc7-9617-5c485218db13
• Query name: CloudWatch S3 policy Change Alarm Missing
• Platform: Terraform
• Severity: Medium
• Category: Observability
• URL: Github

Description

Ensure a log metric filter and alarm exist for S3 bucket policy changes
Documentation

Code samples

Code samples with security vulnerabilities

Postitive test num. 1 - tf file

resource "aws_cloudwatch_log_metric_filter" "cis_s3_bucket_policy_change_metric_filter" {
  name           = "CIS-S3BucketPolicyChanges"
  pattern        = "{ ($.eventSource = \"s3.amazonaws.com\") || (($.eventName = PutBucketAcl) || ($.eventName = PutBucketPolicy) || ($.eventName = PutBucketCors) || ($.eventName = PutBucketLifecycle) || ($.eventName = PutBucketReplication) || ($.eventName = DeleteBucketPolicy) || ($.eventName = DeleteBucketCors) || ($.eventName = DeleteBucketLifecycle) || ($.eventName = DeleteBucketReplication)) }"
  log_group_name = aws_cloudwatch_log_group.CIS_CloudWatch_LogsGroup.name

  metric_transformation {
    name      = "CIS-S3BucketPolicyChanges"
    namespace = "CIS_Metric_Alarm_Namespace"
    value     = "1"
  }
}

resource "aws_cloudwatch_metric_alarm" "cis_s3_bucket_policy_change_cw_alarm" {
  alarm_name                = "CIS-3.8-S3BucketPolicyChanges"
  comparison_operator       = "GreaterThanOrEqualToThreshold"
  evaluation_periods        = "1"
  metric_name               = "XXX NOT YOUR FILTER"
  namespace                 = "CIS_Metric_Alarm_Namespace"
  period                    = "300"
  statistic                 = "Sum"
  threshold                 = "1"
  alarm_description         = "Monitoring changes to S3 bucket policies may reduce time to detect and correct permissive policies on sensitive S3 buckets."
  alarm_actions             = [aws_sns_topic.CIS_Alerts_SNS_Topic.arn]
  insufficient_data_actions = []
}


resource "aws_cloudwatch_log_metric_filter" "cis_no_mfa_console_signin_metric_filter" {
  name           = "CIS-ConsoleSigninWithoutMFA"
  pattern        = "{ ($.eventName = \"ConsoleLogin\") && ($.additionalEventData.MFAUsed != \"Yes\") }"
  log_group_name = aws_cloudwatch_log_group.CIS_CloudWatch_LogsGroup.name

  metric_transformation {
    name      = "CIS-ConsoleSigninWithoutMFA"
    namespace = "CIS_Metric_Alarm_Namespace"
    value     = "1"
  }
}

resource "aws_cloudwatch_metric_alarm" "cis_no_mfa_console_signin_cw_alarm" {
  alarm_name                = "CIS-3.2-ConsoleSigninWithoutMFA"
  comparison_operator       = "GreaterThanOrEqualToThreshold"
  evaluation_periods        = "1"
  metric_name               = aws_cloudwatch_log_metric_filter.cis_no_mfa_console_signin_metric_filter.id
  namespace                 = "CIS_Metric_Alarm_Namespace"
  period                    = "300"
  statistic                 = "Sum"
  threshold                 = "1"
  alarm_description         = "Monitoring for single-factor console logins will increase visibility into accounts that are not protected by MFA."
  alarm_actions             = [aws_sns_topic.CIS_Alerts_SNS_Topic.arn]
  insufficient_data_actions = []
}

Postitive test num. 2 - tf file

resource "aws_cloudwatch_log_metric_filter" "cis_s3_bucket_policy_change_metric_filter" {
  name           = "CIS-S3BucketPolicyChanges"
  pattern        = "{ ($.eventSource = \"s3.amazonaws.com\") && (($.eventName = PutBucketPolicy) || ($.eventName = PutBucketCors) || ($.eventName = PutBucketLifecycle) || ($.eventName = PutBucketReplication) || ($.eventName = DeleteBucketPolicy) || ($.eventName = DeleteBucketCors) || ($.eventName = DeleteBucketLifecycle) || ($.eventName = DeleteBucketReplication)) }"
  log_group_name = aws_cloudwatch_log_group.CIS_CloudWatch_LogsGroup.name

  metric_transformation {
    name      = "CIS-S3BucketPolicyChanges"
    namespace = "CIS_Metric_Alarm_Namespace"
    value     = "1"
  }
}

resource "aws_cloudwatch_metric_alarm" "CIS_S3_Bucket_Policy_Change_CW_Alarm" {
  alarm_name                = "CIS-3.8-S3BucketPolicyChanges"
  comparison_operator       = "GreaterThanOrEqualToThreshold"
  evaluation_periods        = "1"
  metric_name               = aws_cloudwatch_log_metric_filter.cis_s3_bucket_policy_change_metric_filter.id
  namespace                 = "CIS_Metric_Alarm_Namespace"
  period                    = "300"
  statistic                 = "Sum"
  threshold                 = "1"
  alarm_description         = "Monitoring changes to S3 bucket policies may reduce time to detect and correct permissive policies on sensitive S3 buckets."
  alarm_actions             = [aws_sns_topic.CIS_Alerts_SNS_Topic.arn]
  insufficient_data_actions = []
}

Postitive test num. 3 - tf file

resource "aws_cloudwatch_log_metric_filter" "cis_s3_bucket_policy_change_metric_filter" {
  name           = "CIS-S3BucketPolicyChanges"
  pattern        = "{ ($.eventSource = \"s3.amazonaws.com\") && (($.eventName = PutBucketAcl) || ($.eventName = PutBucketCors) || ($.eventName = PutBucketLifecycle) || ($.eventName = PutBucketReplication) || ($.eventName = DeleteBucketPolicy) || ($.eventName = DeleteBucketCors) || ($.eventName = DeleteBucketLifecycle) || ($.eventName = DeleteBucketReplication)) }"
  log_group_name = aws_cloudwatch_log_group.CIS_CloudWatch_LogsGroup.name

  metric_transformation {
    name      = "CIS-S3BucketPolicyChanges"
    namespace = "CIS_Metric_Alarm_Namespace"
    value     = "1"
  }
}

resource "aws_cloudwatch_metric_alarm" "CIS_S3_Bucket_Policy_Change_CW_Alarm" {
  alarm_name                = "CIS-3.8-S3BucketPolicyChanges"
  comparison_operator       = "GreaterThanOrEqualToThreshold"
  evaluation_periods        = "1"
  metric_name               = aws_cloudwatch_log_metric_filter.cis_s3_bucket_policy_change_metric_filter.id
  namespace                 = "CIS_Metric_Alarm_Namespace"
  period                    = "300"
  statistic                 = "Sum"
  threshold                 = "1"
  alarm_description         = "Monitoring changes to S3 bucket policies may reduce time to detect and correct permissive policies on sensitive S3 buckets."
  alarm_actions             = [aws_sns_topic.CIS_Alerts_SNS_Topic.arn]
  insufficient_data_actions = []
}

Postitive test num. 4 - tf file

resource "aws_cloudwatch_log_metric_filter" "cis_s3_bucket_policy_change_metric_filter" {
  name           = "CIS-S3BucketPolicyChanges"
  pattern        = "{ $.eventSource = \"s3.amazonaws.com\" }"
  log_group_name = aws_cloudwatch_log_group.CIS_CloudWatch_LogsGroup.name

  metric_transformation {
    name      = "CIS-S3BucketPolicyChanges"
    namespace = "CIS_Metric_Alarm_Namespace"
    value     = "1"
  }
}

resource "aws_cloudwatch_metric_alarm" "CIS_S3_Bucket_Policy_Change_CW_Alarm" {
  alarm_name                = "CIS-3.8-S3BucketPolicyChanges"
  comparison_operator       = "GreaterThanOrEqualToThreshold"
  evaluation_periods        = "1"
  metric_name               = aws_cloudwatch_log_metric_filter.cis_s3_bucket_policy_change_metric_filter.id
  namespace                 = "CIS_Metric_Alarm_Namespace"
  period                    = "300"
  statistic                 = "Sum"
  threshold                 = "1"
  alarm_description         = "Monitoring changes to S3 bucket policies may reduce time to detect and correct permissive policies on sensitive S3 buckets."
  alarm_actions             = [aws_sns_topic.CIS_Alerts_SNS_Topic.arn]
  insufficient_data_actions = []
}

Code samples without security vulnerabilities

Negative test num. 1 - tf file

resource "aws_cloudwatch_log_metric_filter" "cis_s3_bucket_policy_change_metric_filter" {
  name           = "CIS-S3BucketPolicyChanges"
  pattern        = "{ ($.eventSource = \"s3.amazonaws.com\") && (($.eventName = PutBucketAcl) || ($.eventName = PutBucketPolicy) || ($.eventName = PutBucketCors) || ($.eventName = PutBucketLifecycle) || ($.eventName = PutBucketReplication) || ($.eventName = DeleteBucketPolicy) || ($.eventName = DeleteBucketCors) || ($.eventName = DeleteBucketLifecycle) || ($.eventName = DeleteBucketReplication)) }"
  log_group_name = aws_cloudwatch_log_group.CIS_CloudWatch_LogsGroup.name

  metric_transformation {
    name      = "CIS-S3BucketPolicyChanges"
    namespace = "CIS_Metric_Alarm_Namespace"
    value     = "1"
  }
}

resource "aws_cloudwatch_metric_alarm" "cis_s3_bucket_policy_change_cw_alarm" {
  alarm_name                = "CIS-3.8-S3BucketPolicyChanges"
  comparison_operator       = "GreaterThanOrEqualToThreshold"
  evaluation_periods        = "1"
  metric_name               = aws_cloudwatch_log_metric_filter.cis_s3_bucket_policy_change_metric_filter.id
  namespace                 = "CIS_Metric_Alarm_Namespace"
  period                    = "300"
  statistic                 = "Sum"
  threshold                 = "1"
  alarm_description         = "Monitoring changes to S3 bucket policies may reduce time to detect and correct permissive policies on sensitive S3 buckets."
  alarm_actions             = [aws_sns_topic.CIS_Alerts_SNS_Topic.arn]
  insufficient_data_actions = []
}

resource "aws_cloudwatch_log_metric_filter" "cis_no_mfa_console_signin_metric_filter" {
  name           = "CIS-ConsoleSigninWithoutMFA"
  pattern        = "{ ($.eventName = \"ConsoleLogin\") && ($.additionalEventData.MFAUsed != \"Yes\") }"
  log_group_name = aws_cloudwatch_log_group.CIS_CloudWatch_LogsGroup.name

  metric_transformation {
    name      = "CIS-ConsoleSigninWithoutMFA"
    namespace = "CIS_Metric_Alarm_Namespace"
    value     = "1"
  }
}

resource "aws_cloudwatch_metric_alarm" "cis_no_mfa_console_signin_cw_alarm" {
  alarm_name                = "CIS-3.2-ConsoleSigninWithoutMFA"
  comparison_operator       = "GreaterThanOrEqualToThreshold"
  evaluation_periods        = "1"
  metric_name               = aws_cloudwatch_log_metric_filter.cis_no_mfa_console_signin_metric_filter.id
  namespace                 = "CIS_Metric_Alarm_Namespace"
  period                    = "300"
  statistic                 = "Sum"
  threshold                 = "1"
  alarm_description         = "Monitoring for single-factor console logins will increase visibility into accounts that are not protected by MFA."
  alarm_actions             = [aws_sns_topic.CIS_Alerts_SNS_Topic.arn]
  insufficient_data_actions = []
}