IAM permission boundaries are an advanced feature in AWS Identity and Access Management that sets the maximum permissions an IAM entity (user or role) can have. Think of it as a guardrail that limits what permissions can be granted, even if broader policies are attached.
Permission boundaries work…IAM permission boundaries are an advanced feature in AWS Identity and Access Management that sets the maximum permissions an IAM entity (user or role) can have. Think of it as a guardrail that limits what permissions can be granted, even if broader policies are attached.
Permission boundaries work alongside identity-based policies using an intersection model. For a user to perform an action, BOTH the permission boundary AND the identity-based policy must allow it. If either denies or doesn't include the permission, the action is denied.
Key use cases include:
1. **Delegated Administration**: Organizations can allow developers or team leads to create IAM users and roles while ensuring they cannot grant permissions beyond what the boundary allows. This prevents privilege escalation.
2. **Limiting Service Account Permissions**: When creating service roles, boundaries ensure applications cannot exceed their intended scope of access.
3. **Multi-tenant Environments**: Different teams can manage their own IAM resources while staying within defined limits.
To implement permission boundaries:
- Create an IAM policy defining maximum allowed permissions
- Attach it as a boundary when creating users or roles
- Use the AWS Console, CLI, or CloudFormation
Important considerations for the SysOps exam:
- Boundaries only limit identity-based policy permissions; they do not grant permissions themselves
- Resource-based policies and service control policies (SCPs) are evaluated separately
- Session policies can further restrict permissions during role assumption
- Boundaries apply to IAM users and roles, not groups
Best practices include using AWS managed policies as starting templates, testing boundaries thoroughly before production deployment, and combining them with SCPs for comprehensive access control across your AWS organization.
Understanding permission boundaries is essential for implementing least-privilege access and maintaining security compliance in enterprise AWS environments.
IAM Permission Boundaries: Complete Guide for AWS SysOps Administrator Associate Exam
What Are IAM Permission Boundaries?
IAM Permission Boundaries are an advanced feature that sets the maximum permissions that an identity-based policy can grant to an IAM entity (user or role). Think of it as a guardrail that limits what permissions can be effective, even if broader permissions are granted through other policies.
Why Are Permission Boundaries Important?
Permission boundaries are crucial for several reasons:
• Delegation of Administration: They allow administrators to delegate user creation to other users while ensuring those new users cannot exceed certain permission limits.
• Least Privilege Enforcement: They help enforce the principle of least privilege by capping the maximum permissions regardless of attached policies.
• Security Guardrails: They prevent privilege escalation by limiting what actions delegated administrators can grant.
• Compliance Requirements: They help meet regulatory requirements by ensuring users cannot obtain excessive permissions.
How Do Permission Boundaries Work?
Permission boundaries work through an intersection model:
• The effective permissions are the intersection of the permission boundary AND the identity-based policies.
• If a permission is not allowed in the boundary, it will NOT be effective even if an attached policy grants it.
• Permission boundaries do NOT grant permissions on their own - they only limit what permissions CAN be granted.
Example Scenario:
If a user has an identity-based policy granting full S3 access, but their permission boundary only allows S3:GetObject and S3:ListBucket, the user can ONLY perform GetObject and ListBucket operations on S3.
Key Technical Details:
• Permission boundaries can only be attached to users and roles, NOT groups.
• They use standard IAM policy syntax (JSON format).
• AWS managed policies or customer managed policies can be used as permission boundaries.
• You can only attach ONE permission boundary per IAM entity.
• Permission boundaries affect identity-based policies but do NOT affect resource-based policies.
Permission Evaluation Logic:
When AWS evaluates permissions, the order is: 1. Check for explicit deny in any policy 2. Check Organizations SCPs (if applicable) 3. Check Permission Boundaries 4. Check Session Policies (if applicable) 5. Check Identity-based and Resource-based policies
All applicable policies must allow the action for it to be permitted.
Common Use Cases:
• Developer Self-Service: Allow developers to create their own IAM roles for Lambda functions while restricting which services those roles can access.
• Multi-Tenant Environments: Ensure tenant administrators cannot grant permissions beyond their designated scope.
• Contractor Access: Limit what permissions contractors can obtain even if they have admin rights within their scope.
Exam Tips: Answering Questions on IAM Permission Boundaries
1. Remember the Intersection Rule: When a question asks about effective permissions with a boundary in place, always calculate the intersection of boundary permissions AND identity-based policy permissions.
2. Boundaries Don't Grant - They Limit: If a question suggests a permission boundary grants access, that answer is incorrect. Boundaries only restrict; they never provide permissions.
3. Watch for Group Scenarios: If a question mentions attaching a permission boundary to a group, this is a trick - permission boundaries CANNOT be attached to groups.
4. Resource-Based Policies Are Separate: Questions may try to confuse you by mixing resource-based policies with permission boundaries. Remember that resource-based policies are evaluated separately and are not limited by permission boundaries.
5. Delegation Scenarios: When you see scenarios about allowing one administrator to create users while limiting those users' permissions, permission boundaries are typically the correct answer.
6. SCPs vs Permission Boundaries: SCPs apply at the organization/OU/account level while permission boundaries apply to individual IAM entities. Know when each is appropriate.
7. One Boundary Per Entity: Remember that only one permission boundary can be attached to each user or role - this may appear in questions about managing multiple boundaries.