Falsely Denied: When Your Own Guardrails Silently Break Your Cloud

A recent analysis of CloudTrail deny events across numerous AWS accounts revealed recurring patterns of misconfigurations leading to financial and operational inefficiencies. Despite appearing as breaches or unauthorized attempts, these are legitimate operations blocked by overly broad policies or missing permissions, termed "falsely denied" events by Firefly. A key pattern identified involves EMR service roles failing to delete EBS volumes upon cluster termination due to missing permissions, resulting in orphaned volumes and unnecessary costs. Another pattern found involves Service Control Policies (SCPs) inadvertently blocking legitimate operations, such as a TeamCity CI/CD server attempting to launch EC2 instances, resulting in thousands of denied attempts and operational slowdowns. These findings highlight a systemic issue with preventive controls in cloud governance, where overly broad policies lead to false deny events, affecting legitimate workflows and causing hidden cost accumulations and operational inefficiencies. Firefly's Event Center, designed to aggregate and filter cloud events, has helped identify these patterns, emphasizing the need for teams to audit CloudTrail for denied events and adjust policies to prevent such inefficiencies.