ABAC in AWS: A Practical Guide

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woman working on laptop with AWS security with ABAC

What Is ABAC?

Attribute-based access control, or ABAC, is a model that controls access to resources based on the attributes of the user and resource. It’s a flexible model that considers a broad range of attributes including user department, time of access, and type of resource to decide on granting access. This model allows for a fine-grained control, making it ideal for large organizations with diverse user roles and resources.

For example, consider a university: A professor and a student can both access the university’s course system, but their access levels differ. The professor might have read-write access while the student only has read access. Even professors might not be allowed to edit course materials when accessing the system from their home. To take another example, ABAC could evaluate access based on network topology. If a user is accessing within a certain network segment, they could be granted access, but users accessing from another segment could be denied access.

Unlike traditional models that only consider the user’s role, ABAC factors in more contextual information, such as the time of access or the user’s location, leading to more secure and precise access control. However, such flexibility comes with its complexity, making it a difficult model to implement correctly.

ABAC vs. RBAC: What Is the Difference?

The difference between Attribute-Based Access Control (ABAC) and Role-Based Access Control (RBAC) lies in how they manage user permissions and access rights. RBAC assigns access based on predefined roles within an organization. Each role is associated with a specific level of access, and users are assigned roles that match their responsibilities. For instance, an “Editor” role may have the permission to read, write, and edit content, but cannot publish it.

ABAC, on the other hand, is more dynamic and granular. It considers specific user, resource, and environmental attributes rather than relying solely on roles. This allows ABAC policies to evaluate a range of attributes, like the user’s department, location, time of access, or even the sensitivity of the resource being accessed, before granting or denying permission.

In RBAC, if a user needs access that their role doesn’t provide, the role must be modified or a new one created. ABAC can handle such exceptions without the need for role modification by simply adjusting policies to evaluate the additional attributes relevant to the user’s access requirements.

This difference means that ABAC can provide more nuanced access control suited to complex environments, which raises the risk of security misconfigurations. RBAC is often simpler to implement but can become unwieldy as the number of roles increases. ABAC’s complexity lies in defining policies that accurately capture the necessary attributes and conditions for access control but can result in more scalable and flexible permission management.

How ABAC Works in AWS?

ABAC (Attribute-Based Access Control) lets you define different access levels, even for multiple users operating under the same IAM (Identity and Access Management) role, by focusing on user attributes. You can specify these attributes within AWS itself or transfer them from your existing identity provider (IdP) into AWS via IAM or Amazon Cognito, or also through AWS IAM Identity Center (the upgraded version of AWS SSO).

Using these attributes, you can craft IAM policies to ensure users can only access AWS resources with attribute compatibility. This strategy aids in minimizing the requirement for multiple IAM roles for different use cases within your AWS account.

ABAC also provides the capability to identify the origin of actions performed using IAM roles. For instance, the IAM SourceIdentity attribute is recorded in AWS CloudTrail for each action executed within AWS through an IAM role. By setting the SourceIdentity attribute, you can associate any AWS CloudTrail event with the specific user or application responsible for its execution. This works even in role chain scenarios, where a user assumes another IAM role by using one IAM role, allowing you to track the specific user involved in each action.

ABAC in AWS: A Checklist

The following steps will guide you in setting up and configuring your AWS resources and IAM Identity Center for Attribute-Based Access Control (ABAC):

  1. To start using ABAC in IAM Identity Center, your first task is tagging all AWS resources for which ABAC will be implemented.
  1. Learn how to connect your identity source to your IAM Identity Center, ensuring it includes the relevant user identities and attributes from your identity store. The IAM Identity Center lets you use user attributes from any supported identity source.
  1. Decide on the attributes you want to utilize for access control in AWS based on your needs, then send them to IAM Identity Center. Here are some criteria to consider:
  2. If an external identity provider (IdP) is in use, you need to decide whether to use attributes from the IdP or select attributes from IAM Identity Center directly.
  3. If you prefer your IdP to transfer attributes, arrange your IdP to deliver the attributes via SAML assertions. The procedure for your specific IdP will have Optional sections for instructions.
  4. If your identity source is an IdP and you choose to select attributes through IAM Identity Center, configure SCIM to retrieve attribute values from your IdP. In cases where SCIM can’t work with your IdP, you can manually add users and their attributes via the IAM Identity Center console User page.
  5. If you’re using Active Directory or IAM Identity Center as your identity source, or if you have an IdP and opt to select attributes in IAM Identity Center, check the available attributes you can modify.
  1. Visit the IAM Identity Center console’s Access Control Attributes page to select the attributes you’ll use for ABAC. This will be from the identity source configured in Step 2. After ensuring that all identities and their attributes are in IAM Identity Center, you’ll need to generate key-value pairs (mappings) to be sent to your AWS accounts for access control decisions.
  1. Create custom permission policies under your permission sets, and use access control attributes to form ABAC rules. This ensures users can only access resources that bear matching tags. The attributes you chose in Step 4 will serve as tags in AWS for access control decisions. You can reference these access control attributes in the permissions policy using the aws:PrincipalTag/key condition.
  1. Finally, link users to the permissions sets created in Step 5 across your various AWS accounts. This ensures that users will only be able to access AWS resources based on matching tags when they federate into their accounts.

Conclusion

In conclusion, ABAC on AWS provides a sophisticated framework for managing access to resources, surpassing traditional role-based mechanisms with its dynamic and fine-grained control capabilities. By leveraging attributes pertaining to user, resource, and context, ABAC enables precise permission policies that can adapt to the complexity and scale of modern cloud environments.

Implementing ABAC within AWS requires a thorough understanding of IAM Identity Center, IAM policies, and resource tagging. By tagging AWS resources and configuring identity attributes, organizations can craft policies that govern access not just by ‘who’ a user is, but also by ‘what’ their attributes imply about their access needs.

By integrating ABAC with AWS tools like IAM Identity Center and AWS CloudTrail, organizations can streamline access management and enhance security postures. As a result, ABAC on AWS not only simplifies the necessary conditions for compliance and governance but also aligns with the evolving demands of resource access in cloud computing.

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