Post Syndicated from Mathangi Ramesh original https://aws.amazon.com/blogs/security/use-iam-access-analyzer-to-generate-iam-policies-based-on-access-activity-found-in-your-organization-trail/

In April 2021, AWS Identity and Access Management (IAM) Access Analyzer added policy generation to help you create fine-grained policies based on AWS CloudTrail activity stored within your account. Now, we’re extending policy generation to enable you to generate policies based on access activity stored in a designated account. For example, you can use AWS Organizations to define a uniform event logging strategy for your organization and store all CloudTrail logs in your management account to streamline governance activities. You can use Access Analyzer to review access activity stored in your designated account and generate a fine-grained IAM policy in your member accounts. This helps you to create policies that provide only the required permissions for your workloads.

Customers that use a multi-account strategy consolidate all access activity information in a designated account to simplify monitoring activities. By using AWS Organizations, you can create a trail that will log events for all Amazon Web Services (AWS) accounts into a single management account to help streamline governance activities. This is sometimes referred to as an organization trail. You can learn more from Creating a trail for an organization. With this launch, you can use Access Analyzer to generate fine-grained policies in your member account and grant just the required permissions to your IAM roles and users based on access activity stored in your organization trail.

When you request a policy, Access Analyzer analyzes your activity in CloudTrail logs and generates a policy based on that activity. The generated policy grants only the required permissions for your workloads and makes it easier for you to implement least privilege permissions. In this blog post, I’ll explain how to set up the permissions for Access Analyzer to access your organization trail and analyze activity to generate a policy. To generate a policy in your member account, you need to grant Access Analyzer limited cross-account access to access the Amazon Simple Storage Service (Amazon S3) bucket where logs are stored and review access activity.

Generate a policy for a role based on its access activity in the organization trail

In this example, you will set fine-grained permissions for a role used in a development account. The example assumes that your company uses Organizations and maintains an organization trail that logs all events for all AWS accounts in the organization. The logs are stored in an S3 bucket in the management account. You can use Access Analyzer to generate a policy based on the actions required by the role. To use Access Analyzer, you must first update the permissions on the S3 bucket where the CloudTrail logs are stored, to grant access to Access Analyzer.

To grant permissions for Access Analyzer to access and review centrally stored logs and generate policies

1. Sign in to the AWS Management Console using your management account and go to S3 settings.
2. Select the bucket where the logs from the organization trail are stored.
3. Change object ownership to bucket owner preferred. To generate a policy, all of the objects in the bucket must be owned by the bucket owner.
4. Update the bucket policy to grant cross-account access to Access Analyzer by adding the following statement to the bucket policy. This grants Access Analyzer limited access to the CloudTrail data. Replace the <organization-bucket-name>, and <organization-id> with your values and then save the policy.

   {
       "Version": "2012-10-17",
       "Statement": 
       [
       {
           "Sid": "PolicyGenerationPermissions",
           "Effect": "Allow",
           "Principal": {
               "AWS": "*"
           },
           "Action": [
               "s3:GetObject",
               "s3:ListBucket"
           ],
           "Resource": [
               "arn:aws:s3:::<organization-bucket-name>",
               "arn:aws:s3:::my-organization-bucket/AWSLogs/o-exampleorgid/${aws:PrincipalAccount}/*
   "
           ],
           "Condition": {
   "StringEquals":{
   "aws:PrincipalOrgID":"<organization-id>"
   },
   
               "StringLike": {"aws:PrincipalArn":"arn:aws:iam::${aws:PrincipalAccount}:role/service-role/AccessAnalyzerMonitorServiceRole*"            }
           }
       }
       ]
   }
   

By using the preceding statement, you’re allowing listbucket and getobject for the bucket my-organization-bucket-name if the role accessing it belongs to an account in your Organizations and has a name that starts with AccessAnalyzerMonitorServiceRole. Using aws:PrincipalAccount in the resource section of the statement allows the role to retrieve only the CloudTrail logs belonging to its own account. If you are encrypting your logs, update your AWS Key Management Service (AWS KMS) key policy to grant Access Analyzer access to use your key.

Now that you’ve set the required permissions, you can use the development account and the following steps to generate a policy.

To generate a policy in the AWS Management Console

1. Use your development account to open the IAM Console, and then in the navigation pane choose Roles.
2. Select a role to analyze. This example uses AWS_Test_Role.
3. Under Generate policy based on CloudTrail events, choose Generate policy, as shown in Figure 1.
    
   
   

   Figure 1: Generate policy from the role detail page

4. In the Generate policy page, select the time window for which IAM Access Analyzer will review the CloudTrail logs to create the policy. In this example, specific dates are chosen, as shown in Figure 2.
    
   
   

   Figure 2: Specify the time period

5. Under CloudTrail access, select the organization trail you want to use as shown in Figure 3.
   
   

   Note: If you’re using this feature for the first time: select create a new service role, and then choose Generate policy.

   This example uses an existing service role “AccessAnalyzerMonitorServiceRole_MBYF6V8AIK.”
    

   

   Figure 3: CloudTrail access

6. After the policy is ready, you’ll see a notification on the role page. To review the permissions, choose View generated policy, as shown in Figure 4.
    
   
   

   Figure 4: Policy generation progress

After the policy is generated, you can see a summary of the services and associated actions in the generated policy. You can customize it by reviewing the services used and selecting additional required actions from the drop down. To refine permissions further, you can replace the resource-level placeholders in the policies to restrict permissions to just the required access. You can learn more about granting fine-grained permissions and creating the policy as described in this blog post.

Conclusion

Access Analyzer makes it easier to grant fine-grained permissions to your IAM roles and users by generating IAM policies based on the CloudTrail activity centrally stored in a designated account such as your AWS Organizations management accounts. To learn more about how to generate a policy, see Generate policies based on access activity in the IAM User Guide.

If you have feedback about this blog post, submit comments in the Comments section below. If you have questions about this blog post, start a new thread on the IAM forum or contact AWS Support.

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