detecting-s3-data-exfiltration-attempts

What this skill does

# Detecting S3 Data Exfiltration Attempts

## When to Use

- When GuardDuty detects anomalous S3 access patterns such as bulk downloads from unusual IPs
- When investigating suspected data breach involving S3-stored sensitive data
- When building detection rules for S3 data loss prevention monitoring
- When responding to Macie alerts about sensitive data being accessed or moved
- When compliance requires monitoring and logging of all access to classified data stores

**Do not use** for preventing data exfiltration (use S3 bucket policies, VPC endpoints, and SCPs), for data classification (use Amazon Macie discovery jobs), or for network-level exfiltration detection (use VPC Flow Logs with network analysis tools).

## Prerequisites

- CloudTrail configured with S3 data event logging (`GetObject`, `PutObject`, `CopyObject`)
- GuardDuty enabled with S3 Protection feature activated
- Amazon Macie enabled for sensitive data discovery in target buckets
- CloudWatch Logs or Athena for querying CloudTrail logs at scale
- VPC endpoint policies configured for S3 access monitoring

## Workflow

### Step 1: Enable S3 Data Event Logging in CloudTrail

Configure CloudTrail to capture all S3 object-level operations for forensic analysis.

```bash
# Enable S3 data events on an existing trail
aws cloudtrail put-event-selectors \
  --trail-name management-trail \
  --event-selectors '[{
    "ReadWriteType": "All",
    "IncludeManagementEvents": true,
    "DataResources": [{
      "Type": "AWS::S3::Object",
      "Values": ["arn:aws:s3:::sensitive-data-bucket/", "arn:aws:s3:::customer-records/"]
    }]
  }]'

# Verify data event configuration
aws cloudtrail get-event-selectors --trail-name management-trail \
  --query 'EventSelectors[*].DataResources' --output json

# Enable GuardDuty S3 Protection
aws guardduty update-detector \
  --detector-id $(aws guardduty list-detectors --query 'DetectorIds[0]' --output text) \
  --data-sources '{"S3Logs":{"Enable":true}}'
```

### Step 2: Query CloudTrail for Anomalous S3 Access Patterns

Analyze CloudTrail logs for bulk download activity, unusual access times, and unfamiliar source IPs.

```bash
# Athena query: Top S3 downloaders by volume in last 24 hours
cat << 'EOF'
SELECT
  useridentity.arn as principal,
  sourceipaddress,
  COUNT(*) as request_count,
  SUM(CAST(json_extract_scalar(requestparameters, '$.bytesTransferredOut') AS bigint)) as bytes_downloaded
FROM cloudtrail_logs
WHERE eventname = 'GetObject'
  AND eventsource = 's3.amazonaws.com'
  AND eventtime > date_add('hour', -24, now())
GROUP BY useridentity.arn, sourceipaddress
ORDER BY request_count DESC
LIMIT 50
EOF

# CloudWatch Logs Insights: S3 GetObject requests from unusual IPs
aws logs start-query \
  --log-group-name cloudtrail-logs \
  --start-time $(date -d "24 hours ago" +%s) \
  --end-time $(date +%s) \
  --query-string '
    fields @timestamp, userIdentity.arn, sourceIPAddress, requestParameters.bucketName, requestParameters.key
    | filter eventName = "GetObject"
    | stats count() as requestCount by sourceIPAddress, userIdentity.arn
    | sort requestCount desc
    | limit 25
  '

# Detect cross-account copies (potential exfiltration)
aws logs start-query \
  --log-group-name cloudtrail-logs \
  --start-time $(date -d "7 days ago" +%s) \
  --end-time $(date +%s) \
  --query-string '
    fields @timestamp, userIdentity.arn, sourceIPAddress, requestParameters.bucketName
    | filter eventName in ["CopyObject", "ReplicateObject", "UploadPart"]
    | filter userIdentity.accountId != "OUR_ACCOUNT_ID"
    | sort @timestamp desc
    | limit 100
  '
```

### Step 3: Review GuardDuty S3 Findings

Check for GuardDuty S3-specific finding types that indicate exfiltration activity.

```bash
# List active S3 exfiltration-related findings
aws guardduty list-findings \
  --detector-id $(aws guardduty list-detectors --query 'DetectorIds[0]' --output text) \
  --finding-criteria '{
    "Criterion": {
      "type": {
        "Eq": [
          "Exfiltration:S3/MaliciousIPCaller",
          "Exfiltration:S3/ObjectRead.Unusual",
          "Discovery:S3/MaliciousIPCaller.Custom",
          "Discovery:S3/BucketEnumeration.Unusual",
          "UnauthorizedAccess:S3/MaliciousIPCaller.Custom",
          "UnauthorizedAccess:S3/TorIPCaller",
          "Impact:S3/AnomalousBehavior.Delete"
        ]
      }
    }
  }' --output json

# Get detailed finding information
aws guardduty get-findings \
  --detector-id $(aws guardduty list-detectors --query 'DetectorIds[0]' --output text) \
  --finding-ids FINDING_IDS \
  --query 'Findings[*].{Type:Type,Severity:Severity,Resource:Resource.S3BucketDetails[0].Name,Action:Service.Action}' \
  --output table
```

### Step 4: Analyze Macie Findings for Sensitive Data Access

Review Macie findings to correlate data sensitivity with access anomalies.

```bash
# List Macie findings for sensitive data exposure
aws macie2 list-findings \
  --finding-criteria '{
    "criterion": {
      "category": {"eq": ["CLASSIFICATION"]},
      "severity.description": {"eq": ["High", "Critical"]}
    }
  }' \
  --sort-criteria '{"attributeName": "updatedAt", "orderBy": "DESC"}' \
  --max-results 25

# Get detailed finding with data classification
aws macie2 get-findings \
  --finding-ids FINDING_IDS \
  --query 'findings[*].{Type:type,Severity:severity.description,Bucket:resourcesAffected.s3Bucket.name,SensitiveDataTypes:classificationDetails.result.sensitiveData[*].category}' \
  --output table

# Run a sensitive data discovery job on target bucket
aws macie2 create-classification-job \
  --job-type ONE_TIME \
  --name "exfiltration-investigation" \
  --s3-job-definition '{
    "bucketDefinitions": [{
      "accountId": "ACCOUNT_ID",
      "buckets": ["sensitive-data-bucket"]
    }]
  }'
```

### Step 5: Build Automated Detection Rules

Create CloudWatch alarms and EventBridge rules for real-time exfiltration detection.

```bash
# CloudWatch metric filter for high-volume S3 downloads
aws logs put-metric-filter \
  --log-group-name cloudtrail-logs \
  --filter-name s3-bulk-download \
  --filter-pattern '{$.eventName = "GetObject" && $.eventSource = "s3.amazonaws.com"}' \
  --metric-transformations '[{
    "metricName": "S3GetObjectCount",
    "metricNamespace": "SecurityMetrics",
    "metricValue": "1",
    "defaultValue": 0
  }]'

# Alarm for anomalous download volume (>1000 objects/hour)
aws cloudwatch put-metric-alarm \
  --alarm-name s3-exfiltration-alert \
  --metric-name S3GetObjectCount \
  --namespace SecurityMetrics \
  --statistic Sum \
  --period 3600 \
  --threshold 1000 \
  --comparison-operator GreaterThanThreshold \
  --evaluation-periods 1 \
  --alarm-actions arn:aws:sns:us-east-1:ACCOUNT:security-alerts

# EventBridge rule for GuardDuty S3 findings
aws events put-rule \
  --name guardduty-s3-exfiltration \
  --event-pattern '{
    "source": ["aws.guardduty"],
    "detail-type": ["GuardDuty Finding"],
    "detail": {
      "type": [{"prefix": "Exfiltration:S3/"}]
    }
  }'
```

### Step 6: Implement Preventive Controls

Deploy bucket policies and VPC endpoint policies to restrict data movement paths.

```bash
# VPC endpoint policy restricting S3 access to specific buckets
aws ec2 modify-vpc-endpoint \
  --vpc-endpoint-id vpce-ENDPOINT_ID \
  --policy-document '{
    "Statement": [{
      "Sid": "RestrictToOwnBuckets",
      "Effect": "Allow",
      "Principal": "*",
      "Action": ["s3:GetObject", "s3:PutObject"],
      "Resource": ["arn:aws:s3:::approved-bucket-1/*", "arn:aws:s3:::approved-bucket-2/*"]
    }]
  }'

# Bucket policy denying access from outside the VPC
aws s3api put-bucket-policy --bucket sensitive-data-bucket --policy '{
  "Version": "2012-10-17",
  "Statement": [{
    "Sid": "DenyNonVpcAccess",
    "Effect": "Deny",
    "Principal": "*",
    "Action": "s3:GetObject",
    "Resource": "arn:aws:s3:::sensitive-data-bucket/*",
    "Condition": {
      "StringNotEquals": {
        "aws:sourceVpce": "vpce-ENDPOINT_ID"
      }
    }