Cross Account Assume Role Without External ID and MFA

Overview

In AWS, the AssumeRole operation allows you to delegate permission to make API requests and manage AWS resources. It's typically used in scenarios where you need to access resources across AWS accounts. However, using AssumeRole without External IDs or Multi-Factor Authentication (MFA) can pose security risks. This help content discusses these risks and offers best practices for IT and Security Engineers managing cross-account roles.

Risks Associated with Not Using External ID or MFA

• Privilege Escalation and Unauthorized Access: Without External IDs, any compromised account with permission to assume a role can access resources in another account, potentially bypassing intended security boundaries.

• Lack of Traceability: MFA adds a layer of security by requiring a second form of authentication before assuming a role. Not using MFA makes it difficult to ensure that only legitimate users are performing actions under assumed roles.

• Increased Risk of Cross-Account Data Breaches: Not using External IDs can make it easier for malicious actors to orchestrate attacks that span multiple accounts, leading to more extensive data breaches.

Best Practices for Securing Cross-Account Access

1. Implement External IDs: These unique identifiers are provided by the trusted entity (the account assuming the role) when making a request to assume a role. This prevents the "confused deputy" problem, where a role can be mistakenly assumed by an unauthorized account.

2. Enforce MFA: Require users to authenticate with a second factor before assuming roles, particularly when accessing sensitive resources or performing high-impact operations.

3. Use Role Session Limits: Define the duration for which the credentials are valid to minimize the window during which stolen credentials can be used.

4. Regular Audits and Reviews: Periodically review IAM policies and practices to ensure they adhere to your organization's security standards. Use AWS CloudTrail logs to monitor and audit role assumption events.

5. Educate Users: Provide training on the importance of security practices related to assuming roles across accounts, including the risks of disabling MFA or not using External IDs.

Value to IT and Security Engineers

For IT and Security Engineers, understanding and implementing these best practices is crucial to safeguarding their AWS environments. The correct application of security measures like External IDs and MFA not only helps prevent unauthorized access but also ensures compliance with internal and external audit requirements. This knowledge allows engineers to design more robust security frameworks that protect critical infrastructure and data across multiple accounts.