No CloudWatch alarm for S3 bucket policy changes

Severity: Medium
Service: Monitoring and alarms
Check ID: CLOUDWATCH_ALARM_S3_POLICY_CHANGES

What this check finds

No metric filter and alarm detect S3 bucket ACL or policy modifications. An attacker can quietly make buckets public by changing policies without triggering any alert. CIS v1.4 §4.8.

Passing looks like: CloudWatch alarm for S3 policy changes configured.

How to fix it

Create a metric filter with pattern covering PutBucketAcl, PutBucketPolicy, PutBucketCors, DeleteBucketPolicy events and add a CloudWatch alarm.

Compliance controls it is evidence for

A failing result counts against these controls in KloudLytics; a passing one is evidence towards them. How compliance mapping works

Compliance controls mapped to No CloudWatch alarm for S3 bucket policy changes
Framework	Controls
CIS AWS Foundations Benchmark v5.0.0	4.8 Ensure S3 bucket policy changes are monitored
NIST SP 800-53 Rev5 (Moderate)	AU-6 Audit Record Review, Analysis, and Reporting CM-5 Access Restrictions for Change SI-4 System Monitoring
NIST Cybersecurity Framework 2.0	PR.AA-05 Access permissions and authorizations are enforced with least privilege DE.AE-02 Adverse events are analyzed DE.CM-01 Networks are monitored
ISO/IEC 27001:2022 Annex A	A.8.9 Configuration management A.8.16 Monitoring activities

Checked on every scan

KloudLytics runs this check each time it scans a connected AWS account, through a read-only role, and lists every affected resource with its region. On Pro and Business a fix is written for the specific resource rather than the general case above. The exact access it needs

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