AWS Security: Permissions Boundaries

1. Introduction

Permissions boundaries are a critical feature in AWS Identity and Access Management (IAM) that allow you to set the maximum permissions a user or role can have. This is particularly useful in environments with multiple teams and varying levels of access requirements.

2. Key Concepts

What are Permissions Boundaries?

Permissions boundaries define the outer limits of permissions for IAM roles or users. They are policy documents that govern the permissions granted to an IAM entity but do not grant permissions on their own.

Key Takeaways:

Permissions boundaries are AWS IAM policies.
They do not grant permissions by themselves.
They help enforce least privilege access.

3. Step-by-Step Process

To create and apply permissions boundaries, follow these steps:

Create a permissions boundary policy.
Attach the permissions boundary to an IAM role or user.
Verify the effective permissions using the IAM Policy Simulator.

Example: Creating a Permissions Boundary

{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Effect": "Allow",
            "Action": "s3:*",
            "Resource": "*"
        },
        {
            "Effect": "Deny",
            "Action": "s3:DeleteObject",
            "Resource": "*"
        }
    ]
}

The above policy allows all S3 actions except for deleting objects.

4. Best Practices

When working with permissions boundaries, consider the following best practices:

Always follow the principle of least privilege.
Regularly review and audit permissions boundaries.
Use descriptive names for policies to clarify their purpose.

5. FAQ

What is the difference between a permissions boundary and an IAM policy?

A permissions boundary defines the maximum permissions a user or role can have, while an IAM policy grants specific permissions.

Can I use permissions boundaries with managed policies?

Yes, permissions boundaries can be used with both managed and inline policies.