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How to Find AWS CloudTrail Trails Missing Alarms for S3 Policy Changes

Monitoring unauthorized API calls will help reveal application errors and may reduce time to detect malicious activity.

info

This security check is part of the CIS Amazon Web Services Benchmarks and is rated severity medium.

Prerequisites

This guide assumes that you have already installed and configured Resoto to collect your AWS resources.

Directions

  1. Execute the following search command in Resoto Shell or Resoto UI:

    > search is(aws_cloud_trail) and trail_is_multi_region_trail=true and trail_status.is_logging=true with(empty, --> is(aws_cloudwatch_log_group) with(any, --> is(aws_cloudwatch_metric_filter) and filter_pattern~"\s*\$\.eventSource\s*=\s*s3.amazonaws.com.+\$\.eventName\s*=\s*PutBucketAcl.+\$\.eventName\s*=\s*PutBucketPolicy.+\$\.eventName\s*=\s*PutBucketCors.+\$\.eventName\s*=\s*PutBucketLifecycle.+\$\.eventName\s*=\s*PutBucketReplication.+\$\.eventName\s*=\s*DeleteBucketPolicy.+\$\.eventName\s*=\s*DeleteBucketCors.+\$\.eventName\s*=\s*DeleteBucketLifecycle.+\$\.eventName\s*=\s*DeleteBucketReplication"))
    ​kind=aws_cloud_trail, ..., region=resoto-poweruser
    ​kind=aws_cloud_trail, ..., account=poweruser-team
  2. Pipe the search command into the dump command:

    > search is(aws_cloud_trail) and trail_is_multi_region_trail=true and trail_status.is_logging=true with(empty, --> is(aws_cloudwatch_log_group) with(any, --> is(aws_cloudwatch_metric_filter) and filter_pattern~"\s*\$\.eventSource\s*=\s*s3.amazonaws.com.+\$\.eventName\s*=\s*PutBucketAcl.+\$\.eventName\s*=\s*PutBucketPolicy.+\$\.eventName\s*=\s*PutBucketCors.+\$\.eventName\s*=\s*PutBucketLifecycle.+\$\.eventName\s*=\s*PutBucketReplication.+\$\.eventName\s*=\s*DeleteBucketPolicy.+\$\.eventName\s*=\s*DeleteBucketCors.+\$\.eventName\s*=\s*DeleteBucketLifecycle.+\$\.eventName\s*=\s*DeleteBucketReplication")) | dump
    ​reported:
    ​ id: /aws/cloudtrail/123
    ​ name: some-name
    ​ ctime: '2022-12-05T22:53:14Z'
    ​ kind: aws_cloud_trail
    ​ age: 2mo28d

    The command output will list the details of all non-compliant aws_cloud_trail resources.

Remediation

  • It is recommended that a metric filter and alarm be established for S3 Bucket Policy Changes.
note

Please refer to the AWS CloudTrail documentation for details.

Further Reading

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