In this article, we’ll discuss how to grant access to AWS resources for a third-party, specifically in the context of a consulting company that needs access to audit resources within your AWS account. This scenario is crucial for those preparing for the AWS Certified Security Specialty exam, especially under the Identity and Access Management (IAM) domain, which contributes 20% to the overall exam score.

Understanding the Importance of Secure Access to AWS Resources

In the cloud computing world, securing resources is a top priority, especially when dealing with external entities that require access to your AWS infrastructure. One common scenario arises when a consulting firm or a third-party vendor needs to access resources like Amazon S3 buckets in a client’s AWS account, usually for tasks like auditing, analysis, or management.

While it may seem convenient to provide the third party with Access Keys or create an IAM user for them, these methods are not the most secure. Sharing Access Keys directly or assigning IAM users can expose your AWS environment to unnecessary risks, particularly when the keys are shared over less secure channels. A better and more secure approach is to leverage IAM Roles with an External ID to grant temporary access to the resources in your AWS account, without jeopardizing the security of your environment.

Why Using IAM Roles with External ID is the Best Approach

IAM Roles are an AWS security feature that allow specific users or services to assume permissions temporarily. The role is granted based on the trust relationship between the two AWS accounts—your account and the consulting firm’s account. In this approach, rather than giving the third-party users long-term credentials (like access keys), they assume the role for a limited time to perform specific tasks.

An External ID adds another layer of security to the role assumption process. The External ID is a unique identifier that the consulting firm must present while assuming the role. This prevents unauthorized parties from impersonating the third-party company and ensures that the right person is assuming the role. This is particularly important in environments where you need to establish a cross-account relationship but still want to minimize the risk of unwanted or accidental access.

By using this method, you ensure that only the legitimate, intended party can assume the role, perform the necessary tasks, and access the required resources—without the risks associated with long-term credentials or direct access.

How to Implement Secure Third-Party Access Using IAM Roles

To securely grant the consulting firm or any third-party access to your AWS resources, such as an S3 bucket, you will need to go through a series of steps. These steps involve creating the right IAM policy, setting up the IAM role, and configuring the external party’s permissions. Let’s break down this process step by step.

Step 1: Creating an IAM Policy to Define Permissions

The first step is to create an IAM policy that defines what actions the third-party users can perform on your AWS resources. For example, if the third party needs to access your S3 bucket, you would create a policy that allows actions such as s3:GetObject, s3:ListBucket, and s3:GetBucketLocation.

This policy grants permissions for reading objects and listing the contents of a specific bucket.

Step 2: Creating an IAM Role for Cross-Account Access

Next, you need to create an IAM role that allows a user in another AWS account to assume it. During the role creation process, you will set the trusted entity as Another AWS Account and input the consulting company’s AWS account number. This step establishes the trust relationship between your AWS account and theirs.

You should also attach the policy you created in Step 1 to the role, ensuring that the consulting firm will have the correct permissions to access the required resources when they assume the role.

Step 3: Adding External ID for Additional Security

To further strengthen the security of this cross-account relationship, you should require the consulting firm to use an External ID when assuming the role. The External ID is a unique string that you generate and provide to the consulting company. They must include this ID when making the call to assume the role, ensuring that only the intended party can assume the role.

Using an External ID reduces the risk of a confused deputy attack, where another unauthorized party might impersonate the legitimate consulting firm. By verifying the External ID, AWS ensures that the third party is exactly who they claim to be.

Step 4: Granting Permissions for the Consulting Company to Assume the Role

Once you have set up the role and attached the necessary policy, you need to grant the users in the consulting company the permission to assume the role. This is done by providing them with an inline policy that explicitly grants permission to call the sts:AssumeRole action on the role you created.

Here’s an example of an inline policy that a user in the consulting firm can attach to their IAM user:

This policy ensures that the consulting company’s users have the necessary permissions to assume the role and access the resources you have shared with them.

Step 5: Switching Roles and Accessing Resources

Once the role is set up and the permissions are configured, the third-party user can switch roles in the AWS Management Console to access your AWS resources. They simply need to provide the AWS account number and the role name, along with the External ID.

This process allows the user to access only the specific resources that you have granted them permission to use, with no need for direct access keys or passwords. The role assumption is temporary and tightly controlled, which significantly reduces the risk of unauthorized access.

Step-by-Step Guide to Granting Access via Roles and External ID

Let’s walk through the steps for securely granting the consulting firm access to resources in your AWS account.

Creating a Secure IAM Policy to Grant Access to AWS Resources

When you need to grant a third-party, such as a consulting company, access to your AWS resources, the most secure method is to use IAM roles along with specific policies. The first step in this process involves creating an IAM policy that defines the permissions for the third-party user. This ensures that they have access only to the resources you intend to share, minimizing the risk of unauthorized access or excessive permissions.

For example, let’s say you need to allow the third-party vendor access to your Amazon S3 bucket for the purpose of auditing or data retrieval. Instead of providing access keys or creating permanent IAM users, you create a policy that grants the necessary permissions for a specific task, such as listing and retrieving objects from your S3 bucket.

Here’s a sample IAM policy that grants the third party the ability to list and get objects from an S3 bucket:

Breakdown of the IAM Policy

This IAM policy is carefully crafted to grant the third party access to specific S3 actions without giving them unnecessary permissions:

1. s3:GetObject: This action allows the user to retrieve objects from the specified S3 bucket (awsproduction345).
2. s3:ListBucket: This permission grants the ability to list the contents of the bucket.
3. s3:GetBucketLocation: This permission allows the user to get the location of the S3 bucket.
4. s3:ListAllMyBuckets: This allows the user to view a list of all buckets in the account. While this permission may seem broad, it’s only granted for the purpose of listing, not modifying or accessing the contents of the buckets.

This policy is an example of a least privilege access model. It ensures the third party only has the permissions necessary for their task—viewing and retrieving data from the specific S3 bucket—without exposing any unnecessary resources or actions.

Creating an IAM Role to Grant Access to a Third Party

Once you’ve defined the IAM policy, the next step is to create an IAM role in your AWS account. This role will enable the third-party consulting firm to assume the defined policy, allowing them to access the resources you’ve shared. Let’s walk through the steps involved in creating an IAM role.

Step 1: Set the Trusted Entity as Another AWS Account

When creating an IAM role, you need to establish a trust relationship between your AWS account and the consulting firm’s AWS account. To do this, you will set the trusted entity as another AWS account, which means that only users from the specified AWS account can assume this role.

• Choose “Another AWS Account” as the trusted entity type.
• Enter the account number of the consulting company that will be assuming the role. This ensures that only users in that specific account can assume this role.
• The trust policy will automatically be set to allow the consulting firm’s account to assume the role.

Step 2: Attach the IAM Policy to the Role

The next step in the role creation process is to attach the policy you created earlier (e.g., the CrossAccountS3Access policy) to the IAM role. This ensures that the consulting firm has the necessary permissions to access the specified S3 bucket once they assume the role. By attaching the policy to the role, you define the exact permissions granted to the user who assumes the role.

Step 3: Include External ID for Extra Security

To ensure the integrity of the access process, it’s important to include an External ID when creating the role. The External ID is a unique identifier that adds an additional layer of security. When the third-party consulting firm attempts to assume the role, they will need to provide the correct External ID in their request.

This is an important security measure to avoid unauthorized access through confused deputy attacks, where another entity might impersonate the third-party company. By using an External ID, you guarantee that only the authorized party can successfully assume the role.

Step 4: Role Creation and ARN Distribution

After creating the IAM role and assigning the necessary policy, you will receive the Role ARN (Amazon Resource Name). This ARN uniquely identifies the role you’ve created. You need to share this ARN with the administrator of the consulting firm’s AWS account, allowing them to configure their system to assume the role.

Make sure that the consulting company understands how to use the ARN and what steps they need to take on their end to successfully assume the role.

Why This Approach Is Secure and Scalable

The use of IAM roles with external IDs is an extremely secure and scalable method for granting third-party access to your AWS resources. By using roles instead of static credentials (e.g., access keys), you greatly reduce the risk of key leakage or misuse. The role assumption process is temporary, meaning that once the task is complete, the permissions can be revoked immediately, reducing the window of access.

Furthermore, using an External ID adds a layer of verification, making sure that only the intended party can assume the role. This method allows you to collaborate with external entities while maintaining control over your resources and adhering to the least privilege principle.

Best Practices for Third-Party Access to AWS Resources

Granting third-party access to AWS resources through IAM roles is one of the most secure ways to manage external access. By creating a well-defined IAM policy, establishing a trust relationship with the external party’s AWS account, and using an External ID, you can maintain full control over your resources while ensuring that third-party users can perform their tasks securely and efficiently.

This approach minimizes the risks associated with sharing access keys or creating IAM users for external parties. It’s also more flexible and easier to manage, as you can grant and revoke access with just a few changes to the role configuration.

For those preparing for the AWS Certified Security Specialty exam, mastering IAM roles, policies, and cross-account access is essential. Gaining hands-on experience and testing your knowledge with practice exams from platforms like ExamLabs can further solidify your understanding and help you succeed in your certification journey.

By following best practices and leveraging IAM roles, you can ensure the security of your AWS resources while enabling necessary collaboration with external entities.

Assigning the IAM Policy to the Role

After successfully creating the IAM policy that defines the permissions for the consulting firm’s access to your AWS resources, the next critical step is to assign this policy to the IAM role. This ensures that when the consulting company assumes the role, they will inherit the permissions outlined in the policy, allowing them to perform the required tasks without exceeding the scope of access granted.

To attach the policy to the IAM role, follow these steps:

1. Navigate to the IAM console in your AWS account and locate the role you’ve created for the third-party consulting firm.
2. Edit the role’s permissions and attach the previously created policy (e.g., CrossAccountS3Access) to the role. This policy governs what actions the consulting firm can take on your resources—such as accessing and listing objects in a specific S3 bucket.

By assigning the policy to the IAM role, you ensure that the third-party users who assume the role will only have access to the permissions you’ve defined. This step is crucial because it ties together the trust relationship between your AWS account and the external company, making sure the consulting firm can only perform the actions you’ve explicitly allowed. Without this step, the role would not have any associated permissions, leaving the consulting company unable to access any resources in your account.

Sharing the Role ARN with the Consulting Company

Once the IAM role is created and the policy has been attached, the next step is to share the Role ARN (Amazon Resource Name) with the administrator of the consulting company’s AWS account. The Role ARN is a globally unique identifier for the role and contains the AWS account number, the role name, and other necessary information to reference the role.

To find the ARN of the IAM role, navigate to the IAM console, locate the role you created, and copy the Role ARN. The ARN will look something like this:

This ARN is what the consulting firm will need to assume the role and access the resources in your AWS account. It acts as the key reference to identify the role in their AWS environment, allowing them to configure their access correctly.

Share the ARN securely with the administrator of the consulting company. They will need it to configure their AWS environment and allow users to switch roles to gain access to the resources you’ve specified.

Enabling the Consulting User to Assume the Role

On the consulting company’s side, the user who needs to access your AWS resources must be granted permission to assume the IAM role you’ve created. In AWS, role assumption is handled through the STS (Security Token Service). You need to configure the user’s IAM policy to explicitly allow them to assume the role.

The process for granting a consulting user permission to assume the role involves the following steps:

1. Log in to the consulting company’s AWS account as an administrator.
2. Navigate to the IAM user who needs to assume the role. This could be the individual responsible for the audit, the system administrator, or another relevant user.
3. Add an inline policy to the user’s permissions. The inline policy should specifically allow the user to assume the role that was created in your AWS account. This step is crucial because it grants the user the ability to interact with the AWS Security Token Service (STS) and request temporary credentials for the role.

In this policy:

• Action specifies sts:AssumeRole, which is the permission needed to assume the role.
• Resource points to the ARN of the IAM role you created, allowing the user to assume this particular role.

Once this policy is attached to the IAM user, the user is authorized to assume the role in your AWS account and gain access to the resources you’ve shared with them.

Switching Roles and Accessing Resources

With the inline policy in place, the user can now proceed to switch roles and access the resources in your AWS account. The role-switching process allows the user to temporarily assume the permissions granted to the IAM role, and by doing so, they can access the specified resources (such as your S3 bucket).

Here’s how the consulting user can switch roles in their AWS Management Console:

1. Log in to their AWS account using their credentials.
2. In the upper-right corner of the console, the user will find an option to Switch Role.
3. The user will need to enter:
   • Your AWS account number.
   • The role name you created and shared with them.
   • The External ID if one is required as part of the trust policy (for additional security).

Once the user provides this information, AWS will verify that the user has permission to assume the role. If everything is correctly configured, they will temporarily assume the role and inherit the permissions you assigned in the policy.

After switching roles, the user can now perform actions such as listing the contents of the S3 bucket or retrieving objects, depending on the permissions granted. Once their task is complete, they can simply return to their own account, effectively ending the temporary access.

Why This Approach is Secure and Scalable

Using IAM roles to grant temporary, controlled access to your AWS resources offers several key benefits over traditional methods such as sharing long-term credentials or creating IAM users for third parties. This method ensures that:

• Access is temporary: Once the task is complete, the user can no longer access the resources unless explicitly allowed again.
• Least privilege principle: The third party only has access to the resources and actions you explicitly define in the IAM policy.
• Auditability and traceability: Role assumptions are logged in AWS CloudTrail, making it easy to track who accessed your resources and when.
• External IDs add an additional layer of security, protecting your account from unauthorized access by preventing impersonation.

This secure and scalable model is essential for collaboration with external entities, such as consulting firms, and is an important security practice when working with sensitive data or critical AWS resources.

A Detailed Overview of Granting Secure Access to AWS Resources Using Cross-Account Roles

When working in AWS, there are times when you may need to provide third-party services or external entities (such as consulting companies, auditing firms, or partners) with access to resources in your account. In such cases, it’s important to adopt a method that ensures both security and ease of management. One of the most efficient and secure ways to achieve this is by using cross-account roles and role assumption.

In this process, the third-party user or entity is granted temporary and controlled access to your AWS resources by assuming a predefined IAM (Identity and Access Management) role. This role grants them the necessary permissions to perform specific tasks within your AWS account, without exposing sensitive information like long-term access keys or permanent IAM user credentials.

Understanding Cross-Account Roles

Cross-account roles are a fundamental AWS feature that allows users from one AWS account to securely access resources in another AWS account. These roles act as a bridge between two accounts, providing a controlled way to grant external entities permission to perform certain actions on your resources. Cross-account roles are particularly useful when working with third-party companies or when collaborating on shared resources, like an S3 bucket or an EC2 instance, without needing to create multiple IAM users or share access keys.

A cross-account role allows the external user to temporarily assume a role in your AWS account, which is a more secure and efficient alternative to manually creating IAM users for them. By leveraging roles, you ensure that only the specific permissions you define are granted, and the access is strictly limited to the required resources.

The Role Assumption Process: How It Works

The process of granting access to a third party via cross-account roles revolves around role assumption. This is a procedure in which the third-party user “assumes” the IAM role you’ve created for them, which grants access to the specific AWS resources they need. Here’s a step-by-step breakdown of how role assumption works:

1. Role Creation: First, you create an IAM role in your AWS account and define the permissions you want to grant to the external user. This could include access to resources such as S3 buckets, EC2 instances, or other services.
2. Define Trust Relationship: The role you create must trust the third-party AWS account. This trust is defined by specifying the AWS account ID of the consulting or external company that will assume the role.
3. Assign Permissions: You then attach an IAM policy to the role that specifies the exact actions the third party can perform on your resources. For example, you might allow them to retrieve files from an S3 bucket, but not modify or delete objects.
4. Role Assumption by Third Party: The external user can now assume the role via the AWS Management Console, AWS CLI, or programmatically via the AWS API. Once the role is assumed, the user gains the permissions associated with that role and can perform the designated tasks within your AWS environment.

Importance of Using External IDs for Security

While cross-account roles provide a secure way to manage external access, there are additional security best practices that further enhance the safety of this approach. One such practice is the use of External IDs. An external ID is a unique identifier that adds an extra layer of security to the role assumption process.

When you create a cross-account role, you can configure the role to require an External ID. This ensures that only the intended party can assume the role, preventing unauthorized users from impersonating the trusted third-party service. The external ID acts as a secret key that must be supplied when the third party assumes the role. If the third party does not include the correct external ID in their assumption request, AWS will deny the request.

Using an External ID mitigates the risk of unauthorized access and confused deputy attacks, where an entity might impersonate the trusted third party and gain access to sensitive resources. It’s a simple yet effective method of securing access to AWS resources and ensuring that only the intended third-party users can perform the tasks they are authorized for.

Security Best Practices and Access Control

When it comes to granting third-party access to your AWS environment, security best practices should always be a priority. Here are some key practices to follow:

1. Principle of Least Privilege: Only grant the minimal permissions necessary for the third party to complete their task. For instance, if a third party needs to read from an S3 bucket, ensure the role only has s3:GetObject permissions, not permissions to delete or upload objects. This helps limit exposure to sensitive data.
2. Temporary Access: By using IAM roles and role assumption, access is always temporary. This is a significant security advantage over static credentials, such as access keys, which could be compromised and lead to prolonged unauthorized access. Temporary credentials are issued when the user assumes the role and automatically expire after a predefined duration.
3. Monitor and Audit Access: Enable AWS CloudTrail and other logging services to track who assumed the role, what actions were performed, and when. This allows you to maintain visibility over all activities conducted by third-party users and helps ensure compliance with security policies.
4. Revoke Access After Use: After the third-party user has completed their tasks, ensure that the permissions and roles are revoked. This minimizes the chance of accidental or malicious access in the future.
5. Use Multi-Factor Authentication (MFA): To add an extra layer of protection, require multi-factor authentication (MFA) for any users who are allowed to assume the cross-account role. MFA enhances the security of the process by requiring an additional verification step when assuming the role.

Summary of the Process and Benefits

To summarize, the process of granting third-party access to AWS resources via cross-account roles involves several key steps:

• Creating an IAM Role in your AWS account that defines the necessary permissions for the third party.
• Establishing a trust relationship by allowing users from the third-party AWS account to assume the role.
• Using external IDs to enhance security and prevent unauthorized access.
• Assigning the IAM policy to the role, ensuring the third-party user only has access to the required resources.
• Allowing the user to assume the role and access your resources temporarily using their own credentials.

By following these best practices, you not only grant secure access to your AWS resources but also maintain complete control over who can access what, how long they can access it, and what actions they can perform.

This method is far more secure and scalable than sharing long-term credentials or creating IAM users for external parties. It ensures that your resources are protected from unauthorized access, while enabling collaboration with third-party vendors, auditors, or consultants in a controlled and efficient manner.

For those looking to deepen their understanding of AWS security practices and role management, platforms like ExamLabs offer valuable practice exams and study materials to help you prepare for the AWS Certified Security Specialty exam. By mastering these concepts, you’ll ensure that your AWS environment remains secure while supporting seamless collaboration with external entities.

The Security and Flexibility of IAM Roles with External IDs

Using IAM roles with an external ID is a highly secure way to grant cross-account access. An external ID serves as an additional layer of security, making it much harder for unauthorized users to assume the role and gain access to your resources. By requiring this external ID when the third party attempts to assume the role, you are essentially protecting your account from a confused deputy attack, which can occur if a malicious actor impersonates the trusted external entity.

This method offers a scalable and flexible solution for managing third-party access. Unlike traditional methods that involve creating multiple IAM users or sharing long-term access keys, IAM roles with external IDs provide temporary credentials that automatically expire. This reduces the attack surface and enhances security by ensuring that access is granted only for the necessary period and based on the specific permissions defined within the IAM role.

Furthermore, using IAM roles gives you granular control over what actions third-party users can perform. For instance, if a consulting company needs to review your S3 bucket, you can configure the role to only allow them to list the objects or get specific items without granting full permissions like delete or modify access. This precision helps minimize the risks associated with granting external access to critical resources in your AWS environment.

Why This Approach is Essential for Security and Compliance

Implementing cross-account roles with external IDs is not just a security best practice; it is also essential for compliance with industry standards and regulatory requirements. Many organizations, particularly those in regulated industries, need to maintain strict control over who can access their data and resources. IAM roles, when configured correctly, ensure that only the right individuals and services can perform specific actions.

This control over permissions is critical when working with sensitive data or ensuring that external parties don’t inadvertently breach compliance standards. For example, when sharing access to an S3 bucket containing sensitive customer information, using roles with specific permissions and external IDs helps ensure that only the authorized consulting firm can access that data, and for only as long as necessary.

Moreover, this method reduces the overhead involved in managing multiple IAM users for each third-party collaborator. Instead, by creating one IAM role that can be assumed by any external user, you eliminate the need to manage separate credentials for each user or entity, streamlining administration while maintaining tight security.

Preparing for the AWS Certified Security Specialty Exam

Understanding the intricacies of IAM roles, policies, and cross-account access is crucial, especially if you are preparing for the AWS Certified Security Specialty exam. This certification is designed to test your ability to secure AWS environments, and mastering how to safely manage access for third parties is a core aspect of the exam. By gaining hands-on experience and a deep understanding of IAM roles and how they interact with other AWS services, you will be better equipped to answer complex security-related questions on the exam.

To reinforce your knowledge and ensure you are fully prepared for the certification exam, ExamLabs offers a variety of practice tests, study guides, and other resources that simulate the real exam environment. Practicing with these resources helps solidify your understanding of how to implement security measures like cross-account access and ensures you are well-prepared to handle real-world scenarios.

A Secure and Efficient Workflow for AWS Access Management

In conclusion, by adopting IAM roles with external IDs, AWS users can securely manage third-party access to their resources without compromising security. This method not only provides an additional layer of protection but also enables a more flexible and scalable approach to managing cross-account access. Whether you are working with external auditors, consultants, or partners, this approach ensures that the permissions granted are temporary, tightly controlled, and well-defined.

By carefully following the process of creating IAM policies, assigning them to roles, and granting the necessary permissions to external users, you can implement a highly secure and compliant system for managing access to your AWS environment. This approach reduces the risks associated with sharing permanent credentials, making it a preferred method for managing external access.

For those preparing for the AWS Certified Security Specialty exam, mastering these concepts and gaining practical experience is crucial for passing the exam. Practice tests and exam resources from platforms like ExamLabs will help solidify your knowledge, ensuring that you can confidently implement these security measures in your AWS environment while also preparing for exam success.

Incorporating IAM roles with external IDs is a cornerstone of secure, efficient workflows in AWS, and mastering this technique will prove invaluable, whether you are securing your environment or preparing for AWS certification.

Final Thoughts: 

In today’s increasingly interconnected world, the need to share AWS resources securely with third-party vendors or external entities is more pressing than ever. Whether you’re a company that needs to allow consultants to audit your environment, or you’re collaborating with external partners for specific tasks, granting access to your AWS resources requires a high level of security. One of the most effective and secure ways to manage such access is by utilizing IAM Roles with External IDs.

This approach not only provides fine-grained control over who can access what in your AWS account, but it also enhances security by eliminating the need to share permanent access credentials. Instead of using static IAM user credentials or access keys, IAM roles allow temporary access, reducing the risk of compromised credentials or unauthorized access.