AWS IAM: Least Privilege and Policy Design
Part of the Cybersecurity Skills Guide — This article is one deep-dive in our complete guide series.
By HADESS Team | February 28, 2026 | Updated: February 28, 2026 | 5 min read
IAM is the foundation of AWS security. Every other control — network segmentation, encryption, monitoring — can be bypassed if IAM is misconfigured. Getting IAM right means understanding policy evaluation, writing tight policies, and using guardrails that prevent privilege escalation.
Least Privilege in Practice
Least privilege sounds simple but is hard to implement. Most teams start by attaching AWS managed policies like AmazonS3FullAccess because it is fast. Then those policies never get scoped down.
Start with IAM Access Analyzer. Enable it to generate findings for resources shared outside your account. Then use the policy generation feature: Access Analyzer reviews CloudTrail logs and generates a policy that matches the actual API calls made by a principal over a period you define. This turns observed behavior into a scoped policy.
Use the NotAction element carefully — or better, avoid it. NotAction with Allow does not deny anything; it allows everything except what you listed. This is the opposite of what most people intend.
Policy Conditions
Conditions are where IAM policies get real security value. Without conditions, a policy that allows s3:GetObject on a bucket applies regardless of source IP, MFA status, or request context.
Useful condition keys:
aws:SourceIp— restrict actions to corporate IP rangesaws:MultiFactorAuthPresent— require MFA for sensitive actionsaws:PrincipalOrgID— ensure the caller belongs to your organizationaws:RequestedRegion— prevent actions in unauthorized regionss3:x-amz-server-side-encryption— deny unencrypted uploads
Combine conditions to build policies that reflect your actual security requirements. A role that should only operate from within your VPC, during business hours, with MFA, using encrypted resources — you can express all of that in a single policy statement.
Permission Boundaries
Permission boundaries cap the maximum permissions a principal can have, regardless of what identity-based policies are attached. They are the tool for delegating IAM administration safely.
Set a permission boundary on every IAM role and user. The boundary should exclude dangerous actions: iam:CreateUser without conditions, sts:AssumeRole to privileged roles, organizations:*, and any action on CloudTrail or GuardDuty.
This means even if a developer creates a role with AdministratorAccess, the permission boundary limits what that role can actually do.
Access Analyzer Findings
IAM Access Analyzer produces two types of findings: external access and unused access.
External access findings flag resources (S3 buckets, KMS keys, IAM roles, Lambda functions, SQS queues) that can be accessed by principals outside your account or organization. Review these weekly.
Unused access findings identify IAM roles, access keys, and permissions that have not been used within a configurable window. Use these to remove stale credentials and trim over-provisioned policies.
SCPs as Guardrails
Service Control Policies at the Organization level set hard limits that no IAM policy can override. Use SCPs to:
- Block access to regions you do not use
- Prevent disabling CloudTrail, GuardDuty, or Config
- Deny root account usage except for break-glass scenarios
- Require IMDSv2 on all EC2 instances
Next Steps
- Measure your IAM knowledge with a skills assessment
- Review IAM and related policy skills in the skills library
- Build your cloud security career plan with the coaching tool
Related Guides in This Series
- Active Directory Security: Attack Paths and Hardening — HADESS | 2026
- AWS ALB Security: TLS, Authentication, and Access Controls — HADESS | 2026
- AWS CloudTrail: Log Analysis and Security Monitoring — HADESS | 2026
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