AWS SCP: Implementation, IAM Vs SCP, Best Practices

AWS Service Control Policy (SCP) is a robust management tool within the AWS Organizations feature that provides centralized control over permissions and acts as a guardrail. SCP serves as a crucial layer of defence in the AWS security ecosystem, enabling organizations to proactively protect their cloud environments from unauthorized access and data breaches. SCPs can be used to restrict access to specific AWS services, actions, or resources, or to enforce specific IAM policies across an organization.

Making SCP work in your organization

Each organization has unique requirements when it comes to permissions for users. AWS SCP is powerful and flexible to meet such requirements. SCP and identity and access management (IAM) work in a complimentary way to provide multilevel authentication to strengthen the security of cloud-based assets in your company.  

SCP is like an umbrella control on top of IAM to standardize IAM role permissions across the organization, ensuring that all roles have only the access necessary to perform their designated tasks. Using SCPs, you can restrict which AWS services, resources, and individual API actions the users and roles in each member account can access. You can also define the conditions under which access must be restricted for AWS services, resources, and API actions. Strictly speaking, SCPs do not grant permissions – they deny or allow a set of actions within an organization. IAM is then used to grant permissions to users or roles as needed.

SCPs are not available unless the policy is enabled.  

You can gain maximum benefits by implementing SCPs to:

• Prevent unauthorized resource sharing, both within the organization and with external accounts. This can help protect sensitive data and resources from unauthorized access and potential misuse.
• Restrict access to specific AWS services, such as those that pose higher security risks or are not required for regular operations. This can help contain the attack surface and minimize the potential for unauthorized access.
• Create a centralized mechanism for logging and tracking access control decisions. This audit trail can be used for investigations and to identify potential security breaches or policy violations.
• Prevent users from modifying or disabling tools such as AWS GuardDuty, CloudWatch, and CloudTrail.
• Enable compliance with various regulatory requirements, such as those mandated by industries like healthcare or finance. By defining policies that align with industry standards, SCPs can streamline compliance audits and reduce the risk of non-compliance penalties.
• Deny root user access to prevent takeover attacks using root account.

Differences between SCP and IAM

SCP and IAM seem identical and work on the principle of least privilege access. However, their scope and application vary significantly.  

A user without any IAM permission policies will have no access even if the applicable SCPs allow all services and all actions. If a user or role has an IAM permission for an action that is also allowed by the applicable SCPs, then the user or role can perform that action.  

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In general, SCPs should be used to set high-level security policies, while IAM policies should be used to control access to specific resources and actions. This approach provides a balance of security and flexibility.

Implementing SCP in your organization  

Implementing AWS Service Control Policies (SCPs) effectively in an organization with a single account requires careful planning and execution. Best practices include:

• Evaluate your current IAM policies and resource usage to identify areas where SCPs can add value.
• Create a deny-list as against an allow-list for easy management. Define a deny-list policy that blocks access to all AWS services and actions except those explicitly permitted for your organization's specific needs.
• Divide your SCPs into smaller, more manageable policies that address specific security requirements or resource categories.
• Before attaching SCPs to your production environment, thoroughly test them in a non-production environment to ensure they do not disrupt critical operations.
• Grant exceptions to SCPs only when necessary and with clear justification.
• Regularly monitor and review the effectiveness of your SCPs to ensure alignment with your organization's evolving security needs.
• Utilize organizational units (OUs) to structure SCPs effectively and manage them at the appropriate levels. Apply SCP policies at the OU level instead of the account level for easier troubleshooting.
• Inform users and stakeholders about the purpose and implications of SCPs to foster understanding and compliance.
• Use automation tools to streamline SCP deployment and management to ensure consistent enforcement across the organization.

Conclusion

In a world of evolving cyber threats and complex technological landscapes, AWS Service Control Policies (SCPs) is a powerful tool empowering organizations to implement centralized security controls and enforce consistent security standards across their entire AWS footprint. By restricting access to sensitive resources and ensuring compliance with industry regulations, SCPs play a pivotal role in safeguarding organizational assets and improving an organization's overall security posture.