AWS CloudTrail

Audit AWS account activity with CloudTrail for compliance, security investigation, and operational troubleshooting.

When to Use

• Enabling organization-wide audit logging across all AWS accounts
• Investigating security incidents or unauthorized API activity
• Meeting compliance requirements for SOC 2, HIPAA, PCI DSS, or FedRAMP
• Setting up automated alerting on sensitive AWS API calls
• Querying historical AWS activity for forensic analysis

Create an Organization Trail

# Create the S3 bucket for log storage
aws s3api create-bucket \
  --bucket org-cloudtrail-audit-logs \
  --region us-east-1

# Apply bucket policy allowing CloudTrail to write
aws s3api put-bucket-policy \
  --bucket org-cloudtrail-audit-logs \
  --policy '{
    "Version": "2012-10-17",
    "Statement": [
      {
        "Sid": "AWSCloudTrailAclCheck",
        "Effect": "Allow",
        "Principal": {"Service": "cloudtrail.amazonaws.com"},
        "Action": "s3:GetBucketAcl",
        "Resource": "arn:aws:s3:::org-cloudtrail-audit-logs"
      },
      {
        "Sid": "AWSCloudTrailWrite",
        "Effect": "Allow",
        "Principal": {"Service": "cloudtrail.amazonaws.com"},
        "Action": "s3:PutObject",
        "Resource": "arn:aws:s3:::org-cloudtrail-audit-logs/AWSLogs/*",
        "Condition": {
          "StringEquals": {"s3:x-amz-acl": "bucket-owner-full-control"}
        }
      }
    ]
  }'

# Block public access on the audit bucket
aws s3api put-public-access-block \
  --bucket org-cloudtrail-audit-logs \
  --public-access-block-configuration \
    BlockPublicAcls=true,IgnorePublicAcls=true,BlockPublicPolicy=true,RestrictPublicBuckets=true

# Enable versioning for tamper protection
aws s3api put-bucket-versioning \
  --bucket org-cloudtrail-audit-logs \
  --versioning-configuration Status=Enabled

# Enable server-side encryption
aws s3api put-bucket-encryption \
  --bucket org-cloudtrail-audit-logs \
  --server-side-encryption-configuration '{
    "Rules": [{"ApplyServerSideEncryptionByDefault": {"SSEAlgorithm": "aws:kms", "KMSMasterKeyID": "alias/cloudtrail-key"}}]
  }'

# Set lifecycle policy for log retention
aws s3api put-bucket-lifecycle-configuration \
  --bucket org-cloudtrail-audit-logs \
  --lifecycle-configuration '{
    "Rules": [
      {
        "ID": "TransitionToGlacier",
        "Status": "Enabled",
        "Filter": {"Prefix": "AWSLogs/"},
        "Transitions": [
          {"Days": 90, "StorageClass": "GLACIER"}
        ]
      },
      {
        "ID": "ExpireOldLogs",
        "Status": "Enabled",
        "Filter": {"Prefix": "AWSLogs/"},
        "Expiration": {"Days": 2555}
      }
    ]
  }'

# Create the organization trail
aws cloudtrail create-trail \
  --name org-audit-trail \
  --s3-bucket-name org-cloudtrail-audit-logs \
  --is-organization-trail \
  --is-multi-region-trail \
  --enable-log-file-validation \
  --kms-key-id arn:aws:kms:us-east-1:123456789012:alias/cloudtrail-key \
  --cloud-watch-logs-log-group-arn arn:aws:logs:us-east-1:123456789012:log-group:CloudTrail:* \
  --cloud-watch-logs-role-arn arn:aws:iam::123456789012:role/CloudTrail-CWLogs-Role

# Start logging
aws cloudtrail start-logging --name org-audit-trail

Event Selectors for Management and Data Events

# Configure advanced event selectors for granular control
aws cloudtrail put-event-selectors \
  --trail-name org-audit-trail \
  --advanced-event-selectors '[
    {
      "Name": "AllManagementEvents",
      "FieldSelectors": [
        {"Field": "eventCategory", "Equals": ["Management"]}
      ]
    },
    {
      "Name": "S3DataEventsForSensitiveBuckets",
      "FieldSelectors": [
        {"Field": "eventCategory", "Equals": ["Data"]},
        {"Field": "resources.type", "Equals": ["AWS::S3::Object"]},
        {"Field": "resources.ARN", "StartsWith": [
          "arn:aws:s3:::sensitive-data-bucket/",
          "arn:aws:s3:::pii-bucket/",
          "arn:aws:s3:::financial-data/"
        ]}
      ]
    },
    {
      "Name": "LambdaInvocations",
      "FieldSelectors": [
        {"Field": "eventCategory", "Equals": ["Data"]},
        {"Field": "resources.type", "Equals": ["AWS::Lambda::Function"]}
      ]
    },
    {
      "Name": "DynamoDBDataEvents",
      "FieldSelectors": [
        {"Field": "eventCategory", "Equals": ["Data"]},
        {"Field": "resources.type", "Equals": ["AWS::DynamoDB::Table"]}
      ]
    }
  ]'

CloudWatch Alerts for Sensitive Activity

# Create metric filter for unauthorized API calls
aws logs put-metric-filter \
  --log-group-name CloudTrail \
  --filter-name UnauthorizedAPICalls \
  --filter-pattern '{ ($.errorCode = "*UnauthorizedAccess*") || ($.errorCode = "AccessDenied*") }' \
  --metric-transformations \
    metricName=UnauthorizedAPICalls,metricNamespace=CloudTrailMetrics,metricValue=1

# Create alarm for unauthorized calls
aws cloudwatch put-metric-alarm \
  --alarm-name UnauthorizedAPICallsAlarm \
  --metric-name UnauthorizedAPICalls \
  --namespace CloudTrailMetrics \
  --statistic Sum \
  --period 300 \
  --threshold 5 \
  --comparison-operator GreaterThanOrEqualToThreshold \
  --evaluation-periods 1 \
  --alarm-actions arn:aws:sns:us-east-1:123456789012:security-alerts

# Root account usage alarm
aws logs put-metric-filter \
  --log-group-name CloudTrail \
  --filter-name RootAccountUsage \
  --filter-pattern '{ ($.userIdentity.type = "Root") && ($.userIdentity.invokedBy NOT EXISTS) && ($.eventType != "AwsServiceEvent") }' \
  --metric-transformations \
    metricName=RootAccountUsage,metricNamespace=CloudTrailMetrics,metricValue=1

aws cloudwatch put-metric-alarm \
  --alarm-name RootAccountUsageAlarm \
  --metric-name RootAccountUsage \
  --namespace CloudTrailMetrics \
  --statistic Sum \
  --period 300 \
  --threshold 1 \
  --comparison-operator GreaterThanOrEqualToThreshold \
  --evaluation-periods 1 \
  --alarm-actions arn:aws:sns:us-east-1:123456789012:security-alerts

# Console login without MFA
aws logs put-metric-filter \
  --log-group-name CloudTrail \
  --filter-name ConsoleLoginWithoutMFA \
  --filter-pattern '{ ($.eventName = "ConsoleLogin") && ($.additionalEventData.MFAUsed != "Yes") && ($.userIdentity.type = "IAMUser") }' \
  --metric-transformations \
    metricName=ConsoleLoginWithoutMFA,metricNamespace=CloudTrailMetrics,metricValue=1

# IAM policy changes
aws logs put-metric-filter \
  --log-group-name CloudTrail \
  --filter-name IAMPolicyChanges \
  --filter-pattern '{ ($.eventName=CreatePolicy) || ($.eventName=DeletePolicy) || ($.eventName=AttachRolePolicy) || ($.eventName=DetachRolePolicy) || ($.eventName=AttachUserPolicy) || ($.eventName=PutUserPolicy) }' \
  --metric-transformations \
    metricName=IAMPolicyChanges,metricNamespace=CloudTrailMetrics,metricValue=1

# Security group changes
aws logs put-metric-filter \
  --log-group-name CloudTrail \
  --filter-name SecurityGroupChanges \
  --filter-pattern '{ ($.eventName=AuthorizeSecurityGroupIngress) || ($.eventName=RevokeSecurityGroupIngress) || ($.eventName=CreateSecurityGroup) || ($.eventName=DeleteSecurityGroup) }' \
  --metric-transformations \
    metricName=SecurityGroupChanges,metricNamespace=CloudTrailMetrics,metricValue=1

Athena Queries for CloudTrail Analysis

-- Create Athena table for CloudTrail logs
CREATE EXTERNAL TABLE IF NOT EXISTS cloudtrail_logs (
  eventVersion STRING,
  userIdentity STRUCT<
    type: STRING,
    principalId: STRING,
    arn: STRING,
    accountId: STRING,
    invokedBy: STRING,
    accessKeyId: STRING,
    userName: STRING,
    sessionContext: STRUCT<
      attributes: STRUCT<mfaAuthenticated: STRING, creationDate: STRING>,
      sessionIssuer: STRUCT<type: STRING, principalId: STRING, arn: STRING, accountId: STRING, userName: STRING>
    >
  >,
  eventTime STRING,
  eventSource STRING,
  eventName STRING,
  awsRegion STRING,
  sourceIPAddress STRING,
  userAgent STRING,
  errorCode STRING,
  errorMessage STRING,
  requestParameters STRING,
  responseElements STRING,
  additionalEventData STRING,
  requestId STRING,
  eventId STRING,
  readOnly STRING,
  resources ARRAY<STRUCT<arn: STRING, accountId: STRING, type: STRING>>,
  eventType STRING,
  recipientAccountId STRING
)
PARTITIONED BY (region STRING, year STRING, month STRING, day STRING)
ROW FORMAT SERDE 'org.apache.hive.hcatalog.data.JsonSerDe'
LOCATION 's3://org-cloudtrail-audit-logs/AWSLogs/123456789012/CloudTrail/';

-- Find all delete operations in the last 7 days
SELECT eventTime, userIdentity.arn, eventName, sourceIPAddress,
       requestParameters
FROM cloudtrail_logs
WHERE eventName LIKE '%Delete%'
  AND eventTime > date_format(date_add('day', -7, current_date), '%Y-%m-%dT%H:%i:%sZ')
ORDER BY eventTime DESC
LIMIT 100;

-- Identify console logins from unusual IP addresses
SELECT eventTime, userIdentity.userName, sourceIPAddress,
       additionalEventData
FROM cloudtrail_logs
WHERE eventName = 'ConsoleLogin'
  AND sourceIPAddress NOT IN ('198.51.100.0/24', '203.0.113.0/24')
  AND eventTime > date_format(date_add('day', -30, current_date), '%Y-%m-%dT%H:%i:%sZ')
ORDER BY eventTime DESC;

-- Access key usage patterns per principal
SELECT userIdentity.arn,
       count(*) AS api_call_count,
       count(DISTINCT eventName) AS unique_actions,
       count(DISTINCT sourceIPAddress) AS unique_ips,
       min(eventTime) AS first_seen,
       max(eventTime) AS last_seen
FROM cloudtrail_logs
WHERE eventTime > date_format(date_add('day', -30, current_date), '%Y-%m-%dT%H:%i:%sZ')
GROUP BY userIdentity.arn
ORDER BY api_call_count DESC
LIMIT 50;

-- Failed API calls indicating permission issues or reconnaissance
SELECT eventTime, userIdentity.arn, eventName, errorCode, errorMessage,
       sourceIPAddress
FROM cloudtrail_logs
WHERE errorCode IN ('AccessDenied', 'UnauthorizedAccess', 'Client.UnauthorizedAccess')
  AND eventTime > date_format(date_add('day', -7, current_date), '%Y-%m-%dT%H:%i:%sZ')
ORDER BY eventTime DESC
LIMIT 200;

-- Track KMS key usage
SELECT eventTime, userIdentity.arn, eventName, requestParameters,
       resources[1].arn AS key_arn
FROM cloudtrail_logs
WHERE eventSource = 'kms.amazonaws.com'
  AND eventName IN ('Decrypt', 'Encrypt', 'GenerateDataKey', 'DisableKey', 'ScheduleKeyDeletion')
  AND eventTime > date_format(date_add('day', -7, current_date), '%Y-%m-%dT%H:%i:%sZ')
ORDER BY eventTime DESC;

CloudTrail Lake (Event Data Store)

# Create an event data store for long-term queryable storage
aws cloudtrail create-event-data-store \
  --name org-audit-event-store \
  --multi-region-enabled \
  --organization-enabled \
  --retention-period 2555 \
  --advanced-event-selectors '[
    {
      "Name": "AllManagementEvents",
      "FieldSelectors": [
        {"Field": "eventCategory", "Equals": ["Management"]}
      ]
    }
  ]'

-- CloudTrail Lake SQL queries (run in console or via StartQuery API)
-- Investigate a specific user's activity
SELECT eventTime, eventName, eventSource, sourceIPAddress,
       errorCode, requestParameters
FROM EVENT_DATA_STORE_ID
WHERE userIdentity.arn = 'arn:aws:iam::123456789012:user/suspicious-user'
  AND eventTime > '2024-01-01 00:00:00'
ORDER BY eventTime DESC;

-- Cross-account activity summary
SELECT recipientAccountId, userIdentity.arn,
       count(*) AS event_count
FROM EVENT_DATA_STORE_ID
WHERE eventTime > '2024-01-01 00:00:00'
GROUP BY recipientAccountId, userIdentity.arn
ORDER BY event_count DESC;

Validate Trail Integrity

# Validate log file integrity for a date range
aws cloudtrail validate-logs \
  --trail-arn arn:aws:cloudtrail:us-east-1:123456789012:trail/org-audit-trail \
  --start-time "2024-01-01T00:00:00Z" \
  --end-time "2024-01-31T23:59:59Z"

# Check trail status
aws cloudtrail get-trail-status --name org-audit-trail

# Describe the trail configuration
aws cloudtrail describe-trails --trail-name-list org-audit-trail

Terraform Configuration

resource "aws_cloudtrail" "org_trail" {
  name                          = "org-audit-trail"
  s3_bucket_name                = aws_s3_bucket.cloudtrail.id
  is_organization_trail         = true
  is_multi_region_trail         = true
  enable_log_file_validation    = true
  kms_key_id                    = aws_kms_key.cloudtrail.arn
  cloud_watch_logs_group_arn    = "${aws_cloudwatch_log_group.cloudtrail.arn}:*"
  cloud_watch_logs_role_arn     = aws_iam_role.cloudtrail_cw.arn
  include_global_service_events = true

  advanced_event_selector {
    name = "AllManagementEvents"
    field_selector {
      field  = "eventCategory"
      equals = ["Management"]
    }
  }

  advanced_event_selector {
    name = "SensitiveS3DataEvents"
    field_selector {
      field  = "eventCategory"
      equals = ["Data"]
    }
    field_selector {
      field  = "resources.type"
      equals = ["AWS::S3::Object"]
    }
    field_selector {
      field       = "resources.ARN"
      starts_with = ["arn:aws:s3:::sensitive-data-bucket/"]
    }
  }

  tags = {
    Environment = "production"
    Compliance  = "soc2,hipaa"
  }
}

Setup Checklist

cloudtrail_checklist:
  trail_configuration:
    - [ ] Organization trail enabled across all accounts
    - [ ] Multi-region trail enabled
    - [ ] Log file validation enabled
    - [ ] KMS encryption configured with dedicated key
    - [ ] CloudWatch Logs integration active
    - [ ] S3 bucket policy restricts access to CloudTrail service only

  s3_bucket_hardening:
    - [ ] Public access blocked
    - [ ] Versioning enabled
    - [ ] Server-side encryption enabled
    - [ ] Lifecycle policy set for retention and archival
    - [ ] Access logging enabled on the bucket itself
    - [ ] Object Lock enabled for WORM compliance (if required)

  monitoring_and_alerting:
    - [ ] Metric filters for unauthorized API calls
    - [ ] Alarm on root account usage
    - [ ] Alarm on console login without MFA
    - [ ] Alarm on IAM policy changes
    - [ ] Alarm on security group and NACL changes
    - [ ] Alarm on CloudTrail configuration changes
    - [ ] Alarm on S3 bucket policy changes

  analysis:
    - [ ] Athena table created for ad-hoc queries
    - [ ] CloudTrail Lake event data store for long-term queries
    - [ ] Regular review of high-risk API patterns
    - [ ] Automated reports for compliance evidence

  operational:
    - [ ] Trail status health check automated
    - [ ] Log delivery latency monitored
    - [ ] Log file validation run periodically
    - [ ] SNS notification for trail configuration changes

Best Practices

• Enable organization-wide trails from the management account for full coverage
• Always enable log file validation to detect tampering
• Encrypt logs with a customer-managed KMS key and restrict key usage
• Use advanced event selectors to capture data events on sensitive resources without logging everything
• Integrate with CloudWatch Logs for real-time metric filters and alarms
• Set up Athena or CloudTrail Lake for efficient querying during investigations
• Apply S3 lifecycle policies to transition old logs to Glacier and enforce retention
• Monitor the trail itself (delivery errors, configuration changes) as a meta-control
• Validate log integrity periodically as part of compliance evidence collection
• Restrict access to the CloudTrail S3 bucket and KMS key with least-privilege IAM policies