Stack Permissions in CloudFormation

Excessive IAM Permissions

The Problem

Granting overly broad IAM permissions to CloudFormation stacks can lead to security vulnerabilities, allowing unauthorized access and potential misuse of resources.

Code Examples

Bad Practice

1{
2  "Version": "2012-10-17",
3  "Statement": [
4    {
5      "Effect": "Allow",
6      "Action": "*",
7      "Resource": "*"
8    }
9  ]
10}

‍

Good Practice

1{
2  "Version": "2012-10-17",
3  "Statement": [
4    {
5      "Effect": "Allow",
6      "Action": [
7        "ec2:DescribeInstances",
8        "ec2:RunInstances",
9        "ec2:TerminateInstances"
10      ],
11      "Resource": "arn:aws:ec2:us-west-2:123456789012:instance/*"
12    }
13  ]
14}

Secure Patterns

• Implement the principle of least privilege by granting only the necessary permissions.
• Use IAM Access Analyzer to identify and remove unused permissions.
• Regularly review and update IAM policies to ensure they align with current requirements.

Missing Resource-Level Permissions

The Problem

Failing to implement resource-level permissions can result in overly permissive access to AWS resources, increasing the risk of unauthorized modifications or data breaches.

Code Examples

Bad Practice

1{
2  "Version": "2012-10-17",
3  "Statement": [
4    {
5      "Effect": "Allow",
6      "Action": "s3:*",
7      "Resource": "*"
8    }
9  ]
10}

‍‍

Good Practice

1{
2  "Version": "2012-10-17",
3  "Statement": [
4    {
5      "Effect": "Allow",
6      "Action": [
7        "s3:GetObject",
8        "s3:PutObject"
9      ],
10      "Resource": "arn:aws:s3:::my-bucket/my-prefix/*"
11    }
12  ]
13}

‍

Secure Patterns

• Utilize resource-level permissions to restrict access to specific AWS resources.
• Implement conditional statements in IAM policies to further refine access control.
• Use AWS Organizations and Service Control Policies (SCPs) to enforce organization-wide permission boundaries.

Uncontrolled Cross-Stack References

The Problem

Uncontrolled cross-stack references can lead to unintended dependencies and potential security risks if not properly managed and secured.

Code Examples

Bad Practice

Resources:
  MyEC2Instance:
    Type: AWS::EC2::Instance
    Properties:
      SecurityGroupIds: 
        - Fn::ImportValue: PublicSecurityGroup

‍

Good Practice

Parameters:
  SecurityGroupId:
    Type: AWS::EC2::SecurityGroup::Id
    Description: Security Group ID for EC2 instance

Resources:
  MyEC2Instance:
    Type: AWS::EC2::Instance
    Properties:
      SecurityGroupIds: 
        - !Ref SecurityGroupId

‍

Secure Patterns

• Use explicit parameters for cross-stack references instead of hardcoded imports.
• Implement stack policies to control which resources can be modified or replaced during updates.
• Utilize nested stacks with clearly defined interfaces for better encapsulation and permission management.

‍

Practical Remediation Steps

1. Immediate Actions

• Conduct a comprehensive audit of existing CloudFormation stack permissions using AWS IAM Access Analyzer.
• Implement stack policies for all critical CloudFormation stacks to prevent unauthorized modifications.
• Enable AWS CloudTrail logging for CloudFormation API calls to track and audit changes.
• Review and update service roles used by CloudFormation to ensure they adhere to the principle of least privilege.

2. Long-term Strategy

• Implement a IaC security solution like Gomboc AI
• Regularly update and patch CloudFormation resources to address newly discovered vulnerabilities.
• Implement drift detection and automated remediation to ensure deployed resources match their intended configurations6
• Develop and enforce organizational policies for secure CloudFormation template development, including guidelines for parameter constraints, secret management, and access control3
• Provide ongoing training and education for development and operations teams on CloudFormation security best practices and AWS security services integration3‍

By following these best practices and implementing a comprehensive security strategy, you can significantly enhance the security posture of your CloudFormation stack permissions. Remember that security is an ongoing process, requiring continuous monitoring, improvement, and adaptation to new threats and best practices.

Effective management of stack permissions in CloudFormation is crucial for maintaining a secure and compliant infrastructure as code environment. By addressing issues such as excessive IAM permissions, missing resource-level permissions, and uncontrolled cross-stack references, organizations can significantly reduce their security risks and improve their overall cloud governance.