To enforce least privilege in AWS, grant an IAM identity only the actions its task needs, on the resources it needs, under conditions that fit the task. A practical CLI workflow is to observe activity in CloudTrail, use IAM Access Analyzer to generate a draft policy, check what the draft misses, validate and refine it, then attach and periodically review it. Treat generated output as a starting point—not proof that a policy is complete or safe.
What least privilege means in AWS IAM
IAM users and roles have no permissions by default. Policies grant permissions, so a least-privilege policy should be scoped to the task rather than granting broad access for convenience. Where supported, narrow each statement by action, resource ARN, and condition. AWS Well-Architected guidance describes the goal as granting only the access identities need for specific actions on specific resources under specific conditions: SEC03-BP02: Grant least privilege access.
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Least privilege is not a one-time policy-writing exercise. Workloads and responsibilities change; permissions that once served a task may become unnecessary, while new work may require additional access. Review access over time and remove permissions that are no longer needed.
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Choose a policy starting point
There is no universally best way to produce a least-privilege policy. The best starting point depends on whether you can define the task precisely, whether useful activity has been recorded, and how much review the resulting policy needs.
#1 Best Overall
| Approach | Evidence used | What to watch |
|---|---|---|
| Author a policy manually | The task, required services, and their authorization details | You must identify necessary actions, resources, and conditions; omissions and excessive permissions both require careful review. |
| Start with an AWS managed or job-function policy, then refine | AWS’s predefined permissions for a service or job function | AWS cautions that managed policies may not meet an individual use case’s least-privilege needs. Check and narrow the permissions for your task. |
| Generate a draft with IAM Access Analyzer | CloudTrail activity for an IAM user or role during a selected observation period | Observed activity can miss infrequent work, and the generated policy has specific coverage gaps. Review and customize it before use. |
For background on the managed-policy caveat and AWS’s broader least-privilege guidance, see IAM security best practices.
Generate a policy draft from CloudTrail activity
Access Analyzer policy generation can use CloudTrail events for an IAM user or role to produce a policy template. The setup requires a CloudTrail trail accessible to the generation process, and the activity window can cover up to 90 days. Choose a period that represents the workload, including less frequent but necessary operations where possible. A draft based only on what happened during the selected period may omit work that did not occur then.
- Identify the principal and workload. Determine whether the activity belongs to an IAM user or role and what task the policy must support.
- Check CloudTrail coverage. Ensure the relevant activity is recorded in a trail available to the policy-generation setup. Decide on an observation window appropriate to the workload, up to the documented 90-day maximum.
- Start generation. Use the AWS CLI command
aws accessanalyzer start-policy-generation. Required parameters and current syntax depend on the setup; consult the AWS CLI start-policy-generation reference rather than copying an invocation with assumed values. - Retrieve the result. Use
aws accessanalyzer get-generated-policyand follow the AWS CLI get-generated-policy reference for its current options. The CLI also documentslist-policy-generationsandcancel-policy-generationfor managing generation requests. - Review the draft against the task. Check actions, resources, conditions, cross-account needs, data-event operations, and role-passing requirements independently. The generated policy is a template to inspect and customize, not an audit result.
- Validate and refine before attaching. Correct policy errors and address warnings and suggestions using IAM Access Analyzer validation. Narrow resource ARNs and add conditions where appropriate, then attach the reviewed policy to the intended principal.
- Revisit access. Review the policy when the workload or responsibilities change and remove permissions that are no longer required.
AWS documents the generation workflow and its review guidance in Generating policies based on access activity. The CLI references are the authority for command syntax; the correct parameters and policy scope depend on the trail, principal, services, and resources in your account.
What generated policies can miss
Generated output is useful evidence, but it does not represent every permission a task may need. AWS says policy generation reviews CloudTrail events, including denied actions, but also documents important limitations. A denied event can reveal an attempted action; it does not by itself establish that granting that action is appropriate.
- Data-event action detail: Access Analyzer does not identify action-level activity for data events in generated policies. S3 data events are one example, so verify required data operations separately.
iam:PassRole: This permission is not tracked for this generation workflow and is not included in the generated policy. If the task involves passing a role to an AWS service, assess that permission separately and scope it deliberately.- Service-level rather than action-level detail: For some services, Access Analyzer can identify actions in CloudTrail events; for others, it reports service-level information and requires you to add the relevant actions. Do not assume every service entry is already precise enough.
- Infrequent work: An operation absent from the selected observation window may still be required. Compare the draft with the full task, including occasional maintenance or recovery operations.
- Resource and condition scope: Review whether the draft can be narrowed to specific resource ARNs and conditions. A list of actions alone does not establish that access is limited to the right resources or circumstances.
AWS describes these generation limits and the need to review and customize the result in its policy-generation documentation.
Validate the policy and set permission ceilings
Before deployment, use IAM Access Analyzer policy validation to identify errors, warnings, and suggestions, then decide which findings require changes for your use case. Validation supports review; it does not replace checking that the policy matches the task and its resources.
In an AWS organization, a permissions boundary or an Organizations service control policy (SCP) can limit the maximum permissions available to an identity. These ceilings do not grant permissions on their own: an identity-based or resource-based policy must still grant access. AWS also identifies resource control policies (RCPs) as organization guardrails, not standalone grants. For the distinction between grants and ceilings, see AWS IAM security best practices.
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After attaching a reviewed policy, continue to compare permissions with the work the identity performs. Reassess access when a job changes, a workload adds services or resources, or an operational process is retired. If you use managed policies as a starting point, refine them for the particular task rather than assuming their breadth is appropriate. In multi-account environments, pair organization guardrails with explicit grants on identities or resources; neither an SCP nor an RCP substitutes for those grants.
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