Published on: 2025-11-05

Intelligence Report: Why a CMK Can Be Used Even When Not Permitted by IAM and Key Policies in KMS CMK – Classmethod.jp

1. BLUF (Bottom Line Up Front)

The most supported hypothesis is that AWS KMS grants can override IAM and key policies, allowing CMK usage even when not explicitly permitted by those policies. This is due to the specific permissions granted through AWS KMS grants, which can be more permissive than the policies themselves. Confidence level: High. Recommended action: Review and audit AWS KMS grants regularly to ensure they align with organizational security policies.

2. Competing Hypotheses

Hypothesis 1: AWS KMS grants provide specific permissions that can override IAM and key policies, allowing CMK usage even when not permitted by those policies. This is supported by the ability of grants to authorize specific cryptographic operations and manage access independently of IAM and key policies.

Hypothesis 2: Misconfigurations or errors in IAM or key policies inadvertently allow CMK usage. This could occur if policies are not correctly implemented or updated, leading to unintended access permissions.

Using ACH 2.0, Hypothesis 1 is better supported due to the structured nature of AWS KMS grants, which are designed to provide specific permissions that can override other policy settings.

3. Key Assumptions and Red Flags

Key Assumptions:
– AWS KMS grants are correctly configured and intentionally used to override IAM and key policies.
– IAM and key policies are correctly implemented and do not contain errors.

Red Flags:
– Potential over-reliance on AWS KMS grants without adequate oversight.
– Lack of regular audits on grants and policy configurations.

4. Implications and Strategic Risks

The primary risk is unauthorized access to sensitive data due to misconfigured or overly permissive grants. This could lead to data breaches or unauthorized data manipulation. Additionally, reliance on grants without proper oversight could result in compliance issues and potential exploitation by malicious actors.

5. Recommendations and Outlook

• Conduct regular audits of AWS KMS grants and IAM/key policies to ensure alignment with security protocols.
• Implement automated monitoring and alerting for changes in grant configurations.
• Scenario-based projections:
  • Best Case: Enhanced security posture through regular audits and monitoring, preventing unauthorized access.
  • Worst Case: Data breach due to misconfigured grants, leading to financial and reputational damage.
  • Most Likely: Incremental improvements in security through ongoing audits and policy adjustments.

6. Key Individuals and Entities

Specific individuals are not mentioned in the source text. Entities involved include AWS KMS, IAM, and any organization utilizing these services.

7. Thematic Tags

cybersecurity, cloud security, AWS KMS, data protection, policy management