AWS Organizations
User Guide

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Strategies for Using SCPs

You can configure the SCPs in your organization to work as either of the following:

  • A deny list – actions are allowed by default, and you specify what services and actions are prohibited

  • An allow list – actions are prohibited by default, and you specify what services and actions are allowed

Tip

You can use service last accessed data in IAM to update your SCPs to restrict access to only the AWS services that you need. For more information, see Viewing Organizations Service Last Accessed Data for Organizations in the IAM User Guide.

Using SCPs as a Deny List

The default configuration of AWS Organizations supports using SCPs as deny lists. Using a deny list strategy, account administrators can delegate all services and actions until you create and attach an SCP that denies a specific service or set of actions. Deny statements require less maintenance, because you don't need to update them when AWS adds new services. Deny statements usually use less space, thus making it easier to stay within SCP size limits. In a statement where the Effect element has a value of Deny, you can also restrict access to specific resources, or define conditions for when SCPs are in effect.

To support this, AWS Organizations attaches an AWS managed SCP named FullAWSAccess to every root and OU when it's created. This policy allows all services and actions. It's always available for you to attach or detach from the entities in your organization as needed. Because the policy is an AWS managed SCP, you can't modify or delete it. The policy looks like the following.

{ "Version": "2012-10-17", "Statement": [ { "Effect": "Allow", "Action": "*", "Resource": "*" } ] }

This policy enables account administrators to delegate permissions for any service or action until you create and attach an SCP that denies some access. You can attach an SCP that explicitly prohibits actions that you don't want users and roles in certain accounts to perform.

Such a policy might look like the following example, which prevents users in the affected accounts from performing any actions for the Amazon DynamoDB service. The organization administrator can detach the FullAWSAccess policy and attach this one instead. This SCP still allows all other services and their actions.

{ "Version": "2012-10-17", "Statement": [ { "Sid": "AllowsAllActions", "Effect": "Allow", "Action": "*", "Resource": "*" }, { "Sid": "DenyDynamoDB", "Effect": "Deny", "Action": "dynamodb:*", "Resource": "*" } ] }

The users in the affected accounts can't perform DynamoDB actions because the explicit Deny element in the second statement overrides the explicit Allow in the first. You could also configure this by leaving the FullAWSAccess policy in place and then attaching a second policy that has only the Deny statement in it, as shown here.

{ "Version": "2012-10-17", "Statement": [ { "Effect": "Deny", "Action": "dynamodb:*", "Resource": "*" } ] }

The combination of the FullAWSAccess policy and the Deny statement in the preceding DynamoDB policy that is applied to a root or OU has the same effect as the single policy that contains both statements. All policies that apply at a specified level are combined. Each statement, no matter which policy originated it, is evaluated according to the rules discussed earlier (that is, an explicit Deny overrides an explicit Allow, which overrides the default implicit Deny).

Using SCPs as an Allow List

To use SCPs as an allow list, you must replace the AWS managed FullAWSAccess SCP with an SCP that explicitly permits only those services and actions that you want to allow. By removing the default FullAWSAccess SCP, all actions for all services are now implicitly denied. Your custom SCP then overrides the implicit Deny with an explicit Allow for only those actions that you want to permit. For a permission to be enabled for a specified account, every SCP from the root through each OU in the direct path to the account, and even attached to the account itself, must allow that permission.

An allow list policy might look like the following example, which enables account users to perform operations for Amazon EC2 and Amazon CloudWatch, but no other service. All SCPs in parent OUs and the root also must explicitly allow these permissions.

{ "Version": "2012-10-17", "Statement": [ { "Effect": "Allow", "Action": [ "ec2:*", "cloudwatch:*" ], "Resource": "*" } ] }