Securing AWS Environments with Advanced IAM & Zero Trust

In an era where cloud security is of utmost importance, implementing a zero-trust model is essential. Zero trust means that no user or resource is trusted by default—even those within your network. In this post, I’ll demonstrate how to architect a secure AWS environment by using advanced IAM policies, AWS Organization's SCPs, and AWS Security Hub for continuous monitoring and risk mitigation. This guide includes practical CLI commands, sample outputs, and a real-world case study to illustrate the impact on security posture.

Note: All commands assume that you have the AWS CLI configured with the necessary permissions and that you’re operating in a test or development environment before applying changes in production.

1. Zero Trust and AWS

A zero-trust security model requires verification for every access request—whether the request originates from inside or outside our network. In AWS, this means:

• Strict Identity Verification: Using advanced IAM policies to enforce least privilege and role-based access.
• Boundary Enforcement: Using AWS Organizations and SCPs to control what actions can be performed across multiple AWS accounts.
• Continuous Monitoring: Leveraging AWS Security Hub to detect, report, and remediate any deviation from security best practices.

2. Advanced IAM Policies for Least Privilege

A. Creating a Restrictive IAM Policy
One of the core elements of zero trust is ensuring that every IAM user, role, or service only has permissions necessary for their job functions. Here’s an example of an advanced IAM policy that grants read-only access to S3 buckets and CloudWatch logs—but nothing else.

IAM Policy JSON (ReadOnlyPolicy.json):

{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Sid": "AllowReadOnlyS3",
      "Effect": "Allow",
      "Action": [
        "s3:Get*",
        "s3:List*"
      ],
      "Resource": "*"
    },
    {
      "Sid": "AllowReadOnlyCloudWatch",
      "Effect": "Allow",
      "Action": [
        "logs:Describe*",
        "logs:Get*",
        "logs:List*"
      ],
      "Resource": "*"
    }
  ]
}

B. Applying the Policy

Creating the policy:

aws iam create-policy --policy-name ReadOnlyPolicy --policy-document file://ReadOnlyPolicy.json

Output:

{
  "Policy": {
    "PolicyName": "ReadOnlyPolicy",
    "PolicyId": "ABCDEFGHIJKLMN123456",
    "Arn": "arn:aws:iam::123456789012:policy/ReadOnlyPolicy",
    "Path": "/",
    "DefaultVersionId": "v1",
    "AttachmentCount": 0,
    "PermissionsBoundaryUsageCount": 0,
    "IsAttachable": true,
    "CreateDate": "2025-01-15T12:00:00Z",
    "UpdateDate": "2025-01-15T12:00:00Z"
  }
}

Best Practice: We need to ensure every user or role is attached only to the policies that they require. And also we need to combine this with permission boundaries when delegating administration.

3. Enforcing Boundaries with AWS Organizations and SCPs

AWS Organizations allows us to centrally manage multiple AWS accounts. By applying SCPs, we can enforce security boundaries across all accounts.

A. Example SCP for Zero Trust
Here’s an SCP that denies the use of risky actions (for example, IAM policy modifications) unless explicitly allowed. Let's save this SCP as ZeroTrustSCP.json:

{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Sid": "DenyNonApprovedIAMChanges",
      "Effect": "Deny",
      "Action": [
        "iam:CreatePolicy",
        "iam:DeletePolicy",
        "iam:AttachUserPolicy",
        "iam:DetachUserPolicy",
        "iam:AttachRolePolicy",
        "iam:DetachRolePolicy"
      ],
      "Resource": "*",
      "Condition": {
        "StringNotEquals": {
          "aws:PrincipalTag/ApprovedForIAMChanges": "true"
        }
      }
    }
  ]
}

B. Attaching the SCP via CLI

Let's say we have an Organizational Unit (OU) with ID ou-1234-abcdef, for attaching the SCP:

Create Policy:

aws organizations create-policy \
  --name "ZeroTrustSCP" \
  --description "Deny risky IAM changes unless approved" \
  --type SERVICE_CONTROL_POLICY \
  --content file://ZeroTrustSCP.json

Output:

{
  "Policy": {
    "PolicySummary": {
      "Id": "p-0123456789abcdef",
      "Arn": "arn:aws:organizations::123456789012:policy/o-exampleorgid/p-0123456789abcdef",
      "Name": "ZeroTrustSCP",
      "Description": "Deny risky IAM changes unless approved",
      "Type": "SERVICE_CONTROL_POLICY",
      "AwsManaged": false
    }
  }
}

Then attach the SCP to the OU:

aws organizations attach-policy --policy-id p-0123456789abcdef --target-id ou-1234-abcdef

Best Practice: We need to regularly review and update SCPs to reflect evolving security requirements.

4. Continuous Monitoring with AWS Security Hub

AWS Security Hub aggregates security findings from various AWS services and partner tools, offering a centralized view of our security posture.

A. Enabling Security Hub

aws securityhub enable-security-hub

Output:

{
  "SecurityHubArn": "arn:aws:securityhub:us-east-1:123456789012:hub/default"
}

B. Custom Insights for Zero Trust

We can create a custom insight to monitor for any IAM policy changes that fall outside your defined boundaries. For example, track any unauthorized IAM policy attachments.

Create an Insight (using JSON conf.):

{
  "Name": "UnauthorizedIAMPolicyChanges",
  "Filters": {
    "ResourceType": [
      {
        "Value": "AwsIamPolicy",
        "Comparison": "EQUALS"
      }
    ],
    "ComplianceStatus": [
      {
        "Value": "FAILED",
        "Comparison": "EQUALS"
      }
    ]
  },
  "GroupByAttribute": "ResourceId"
}

Command to create the insight:

aws securityhub create-insight --cli-input-json file://UnauthorizedIAMPolicyChanges.json

Best Practice: Integrate Security Hub with AWS Config and CloudWatch Events for real-time alerting and automated remediation.

5. Case Study: Zero Trust Implementation in a Multi-Account Setup

Scenario

Let's say our organization manages a multi-account AWS environment through AWS Organizations. A misconfigured IAM policy in one of the development accounts resulted in overly permissive access, potentially exposing sensitive data.

Remediation Steps

Advanced IAM Policies:

a. We immediately reviewed all IAM policies and enforced our custom read-only policy.
b. Applied permission boundaries to prevent escalation.

SCP Enforcement:

a. Our ZeroTrustSCP automatically denied risky IAM changes from users lacking the “ApprovedForIAMChanges” tag.
b. We quickly identified and revoked unauthorized policy attachments.

Continuous Monitoring:

a. AWS Security Hub flagged the non-compliant IAM activity through our custom insight.
b. Automated CloudWatch Events triggered remediation scripts to alert security personnel.

Outcome

The implementation of these measures reduced the risk exposure significantly. The zero-trust model ensured that even if an account was compromised, the enforced boundaries prevented lateral movement and unauthorized changes. Regular audits and automated monitoring continue to enhance our security posture.

6. Conclusion

Implementing a zero-trust security model in AWS is not a one-time task but a continuous process. By combining advanced IAM policies, enforcing boundaries through AWS Organizations’ SCPs, and continuously monitoring with AWS Security Hub, we can create a robust security framework that mitigates risk and strengthens our cloud deployments.

Feel free to share your questions or insights in the comments below.

Happy Securing ;)