How a Misconfigured AWS KMS Key Policy Broke Production Access
An NDA Protected Technology Client relied on AWS KMS customer managed keys to protect data across an Amazon PostgreSQL database, S3 data lakes, and AWS Secrets Manager. A Terraform change intended to tighten administrative access removed key-policy permissions required for IAM-based access, leaving production workloads unable to decrypt required credentials.
The resulting KMS access failures caused payment gateway timeouts, customer-facing API errors, and HTTP 500 responses from affected microservices. Bobcares restored administrative access through the documented break-glass procedure, normalized the key policy structure, added OPA checks to CI/CD, and configured CloudWatch monitoring for repeated KMS access-denied events.
Business Challenge
A Terraform change removed the KMS key-policy permissions needed for IAM-based access to the production encryption key. This prevented authorized administrators from managing the key and caused applications dependent on encrypted database credentials to fail, resulting in payment gateway timeouts and customer-facing API errors.
Technology Used
Blueprint
Production applications used a KMS key to protect data in PostgreSQL, S3, and Secrets Manager. The corrected design restored administrative delegation while retaining application runtime access, then added OPA validation to the CI/CD pipeline and CloudWatch monitoring over CloudTrail events to detect repeated KMS access failures.
Key Outcomes
- Restored administrative access to the production KMS key.
- Restored the ability of affected workloads to access encrypted credentials.
- Separated root account delegation, administrative management, and application runtime access within the key policy.
- Added automated validation for KMS policy changes before CI/CD merges.
- Added monitoring for repeated KMS access-denied events.
- Established a tested hardware MFA break-glass procedure for emergency recovery.
Customer Profile
The Challenges
- A Terraform change removed key-policy permissions required for IAM-based access.
- The production KMS key no longer allowed authorized administrators to manage or modify the key.
- Microservices could not decrypt required database credentials through Secrets Manager.
- The payment gateway experienced complete timeouts during the incident.
- Customer-facing APIs returned errors, including HTTP 500 responses.
- Engineers attempting to roll back the policy through the AWS Management Console received AccessDenied errors.
- The existing policy change process did not prevent the misconfigured KMS policy from reaching production.
Why Bobcares?
- Identified the KMS key policy as the source of the production access failure rather than a network infrastructure issue.
- Restored access using the client’s emergency break-glass procedure.
- Restructured the key policy to separate administrative delegation from application runtime access.
- Added policy validation to the existing CI/CD workflow instead of relying only on manual review.
- Introduced monitoring for KMS authorization failures to improve incident visibility.
What We Delivered
- Restored administrative KMS access using
.aws kms put-key-policy - Normalized the KMS key policy into separate blocks for root account delegation, administrative management, and application runtime access.
- Integrated Open Policy Agent into the CI/CD pipeline for static policy validation.
- Applied security rules to pull requests affecting KMS resources.
- Configured a CloudWatch Metric Filter to process relevant CloudTrail events.
- Added alerting for repeated
andkms:Decrypt
access-denied events.kms:GenerateDataKey - Established a hardware MFA break-glass access procedure for emergency KMS recovery.
The Results
Production Access
- Before: Authorized administrators were unable to manage the production KMS key after the key policy removed the required IAM delegation.
- After: Administrative access was restored through the emergency break-glass procedure and the corrected key policy.
Application Availability
- Before: Applications dependent on encrypted credentials experienced KMS access failures, payment gateway timeouts, and customer-facing API errors.
- After: KMS access was restored, allowing affected workloads to resume access to the required encrypted credentials.
Policy Validation
- Before: KMS policy changes relied on manual peer review.
- After: KMS-related changes were automatically checked through OPA in the CI/CD pipeline before merge.
Failure Detection
- Before: KMS access failures were identified through application and user reports during the incident.
- After: CloudWatch monitoring was configured to detect repeated KMS access-denied events from CloudTrail logs.
Emergency Recovery
- Before: Emergency KMS administrative access was not verified through a tested break-glass process.
- After: A hardware MFA-based break-glass procedure was established for emergency recovery.
The Business Impact
- Restored access to encryption keys required by production workloads.
- Reduced the risk of application-wide failures caused by unauthorized KMS access.
- Added a preventive control against invalid KMS policy changes reaching production.
- Improved visibility into repeated KMS authorization failures.
- Provided a defined emergency recovery path for future administrative lockouts.
- Reduced reliance on reactive troubleshooting during KMS-related incidents.
Ongoing Collaboration
- Monitor KMS authorization failures through CloudWatch and CloudTrail.
- Validate future KMS policy changes through automated CI/CD checks.
- Maintain the emergency break-glass procedure for KMS administration.
- Review KMS access controls as infrastructure and security policies evolve.
- Continue monitoring application access to KMS-protected credentials.
Conclusion
A Terraform policy change unintentionally removed the KMS permissions required for administrative and application access, disrupting production workloads and causing customer-facing failures. Bobcares restored access, restructured the key policy, and introduced automated validation and monitoring. The resulting controls provide a safer process for managing KMS policies and detecting access failures before they become prolonged production incidents.
