---
title: S3 bucket policy changes should be monitored
description: Datadog, the leading service for cloud-scale monitoring.
breadcrumbs: >-
  Docs > Datadog Security > OOTB Rules > S3 bucket policy changes should be
  monitored
---

> For the complete documentation index, see [llms.txt](https://docs.datadoghq.com/llms.txt).

# S3 bucket policy changes should be monitored
 
## Description{% #description %}

AWS accounts should have at least one active multi-region CloudTrail trail that captures all management events (an event selector with `IncludeManagementEvents` set to `true` and `ReadWriteType` set to `All`), sends its logs to CloudWatch Logs, and has a metric filter and alarm for S3 bucket policy changes (`PutBucketAcl`, `PutBucketPolicy`, `PutBucketCors`, `PutBucketLifecycle`, `PutBucketReplication`, `DeleteBucketPolicy`, `DeleteBucketCors`, `DeleteBucketLifecycle`, `DeleteBucketReplication` on `s3.amazonaws.com`). The alarm must notify an SNS topic with at least one confirmed subscriber so that permissive policies on sensitive S3 buckets are detected and corrected quickly.

## Remediation{% #remediation %}

1. Create a metric filter on the log group of the active multi-region trail and an SNS topic with a subscription, as described in the [CloudWatch alarms for CloudTrail guide](https://docs.aws.amazon.com/awscloudtrail/latest/userguide/cloudwatch-alarms-for-cloudtrail.html):

```plaintext
aws logs put-metric-filter --log-group-name <trail-log-group-name> \
--filter-name <s3-bucket-policy-changes-metric> --metric-transformations \
metricName=<s3-bucket-policy-changes-metric>,metricNamespace='CISBenchmark',metricValue=1 \
--filter-pattern '{ ($.eventSource = s3.amazonaws.com) && (($.eventName = PutBucketAcl) || ($.eventName = PutBucketPolicy) || ($.eventName = PutBucketCors) || ($.eventName = PutBucketLifecycle) || ($.eventName = PutBucketReplication) || ($.eventName = DeleteBucketPolicy) || ($.eventName = DeleteBucketCors) || ($.eventName = DeleteBucketLifecycle) || ($.eventName = DeleteBucketReplication)) }'
aws sns create-topic --name <sns-topic-name>
aws sns subscribe --topic-arn <sns-topic-arn> --protocol <sns-protocol> --notification-endpoint <sns-subscription-endpoints>
```
Create an alarm on the metric that notifies the SNS topic:
```plaintext
aws cloudwatch put-metric-alarm --alarm-name <s3-bucket-policy-changes-alarm> --metric-name <s3-bucket-policy-changes-metric> \
--statistic Sum --period 300 --threshold 1 --comparison-operator GreaterThanOrEqualToThreshold \
--evaluation-periods 1 --namespace 'CISBenchmark' --alarm-actions <sns-topic-arn>
```

## References{% #references %}

- [Creating CloudWatch alarms for CloudTrail events](https://docs.aws.amazon.com/awscloudtrail/latest/userguide/cloudwatch-alarms-for-cloudtrail.html)
- [Logging management events with CloudTrail](https://docs.aws.amazon.com/awscloudtrail/latest/userguide/logging-management-events-with-cloudtrail.html)
- [Create a metric filter for a log group](https://docs.aws.amazon.com/AmazonCloudWatch/latest/logs/CreateMetricFilterProcedure.html)
- [CIS Amazon Web Services Benchmarks](https://www.cisecurity.org/benchmark/amazon_web_services)