Region deny control applied to the OU
This control is commonly referred to as the OU Region deny control, or the configurable Region deny control.
This control disallows access to unlisted operations in global and regional AWS services, outside of the specified Regions for an organizational unit (OU).
If you enforce this control, the configurations for the OU can conflict with the landing zone version of this control. For more information, see the section called "Policy evaluation of SCP controls" in this chapter, and SCP evaluation in the AWS Organizations doumentation.
CT.MULTISERVICE.PV.1: Deny access to AWS based on the requested AWS Region for an organizational unit
Service: Multiple AWS services
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Control objective: Protect configurations
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Implementation: Service control policy (SCP)
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Control behavior: Preventive
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Control owner: AWS Control Tower
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Groups: Digital sovereignty
Limitations
The OU Region deny control is subject to limitations of the aws:RequestedRegion global condition key and Service Control Policies (SCPs) in general.
Enable this control from the console
In the AWS Control Tower console, you can view the OUs on which this control is enabled, if any, by navigating to the Control details page for this control.
To enable this control from the Control details page
Select Enable control in the upper right
Select the target OU, then select Next to continue.
Select the Regions you wish to activate. You must select at least one Region.
You can add NotAction elements, IAM principals, and tags.
You'll be able to see a summary of your selected values before you enable the control.
Select Enable control at the lower right.
CT.MULTISERVICE.PV.1: Deny access to AWS based on the requested AWS Region for an organizational unit
The OU Region deny control, CT.MULTISERVICE.PV.1, is configurable. You can select specific OUs to which it applies, rather than applying it to your entire AWS Control Tower landing zone. This control accepts one or more parameters, such as AllowedRegions, ExemptedPrincipalARNs, and ExemptedActions, which describe operations that are allowed for accounts that are part of this OU.
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AllowedRegions: Specifies the Regions selected, in which the OU is allowed to operate. This parameter is mandatory.
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ExemptedPrincipalARNs: Specifies the IAM principals that are exempt from this control, so that they are allowed to operate certain AWS services globally.
ExemptedActions: Specifies actions that are exempt from this control, so that the actions are allowed.
Interactions between the separate Region deny controls for the landing zone and the OU can be complicated to predict. They are predictable with the logic by which SCPs are evaluated by AWS.
Policy evaluation of SCP controls
The policy evaluation process involves checking all applicable policies, starting from the most permissive and gradually moving towards the most restrictive. Any SCP applied at the Root level will impact all accounts and OUs, unless it is overridden by a more specific policy.
Evaluation Logic: When a request is made to perform an action (for example, launching an Amazon EC2 instance), AWS evaluates policies to determine whether the action is allowed or denied. The evaluation logic follows these rules:
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Explicit Deny Overrides All: If any policy explicitly denies the requested action, that denial takes precedence over all other policies.
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Explicit Allow Overrides Implicit Deny: If a policy explicitly allows the action and no higher-level policy explicitly denies it, the action is allowed.
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Inherited Allow and No Explicit Deny: If there is no explicit allow or deny at the requested level, AWS looks at higher-level policies. If there is an inherited allow and no explicit deny, the action is allowed.
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Explicit Deny at a Higher Level: If there's an explicit deny in a higher-level policy, but no explicit allow or deny at the requested level, the action is denied.
For more information about the evaluation logic, see SCP evaluation in the AWS Organizations documentation.
Note
With this control, you can allow any AWS Region at the OU level, even if your landing zone does not govern that Region, by design. We recommend that you use caution when allowing Regions that your AWS Control Tower landing zone does not govern.
CLI Example
This example shows how to enable this control, with parameters, from the CLI.
aws controltower enable-control \ --target-identifier arn:aws:organizations::01234567890:ou/o-EXAMPLE/ou-zzxx-zzx0zzz2 \ --control-identifier arn:aws:controltower:us-east-1::control/EXAMPLE_NAME \ --parameters '[{"key":"AllowedRegions","value":["us-east-1","us-west-2"]},{"key":"ExemptedPrincipalArns","value":["arn:aws:iam::*:role/ReadOnly","arn:aws:sts::*:assumed-role/ReadOnly/*"]},{"key":"ExemptedActions","value":["logs:DescribeLogGroups","logs:StartQuery","logs:GetQueryResults"]}]'
Validating parameters
When you enter a parameter into the OU Region deny control, AWS Control Tower validates the parameter's syntax and checks it against JSON datatypes. AWS Control Tower does not make semantic validations for domain-specific correctness. This is the same approach that is followed by AWS Organizations.
Parameters for this control are entered by means of a JSON schema.
Here is the SCP template of an example JSON schema for the OU-level Region deny control. In the AWS Control Tower console, you can view it on the Artifacts tab of the Control details page.
This short example schema shows that the AllowedRegions, ExemptedActions and
ExemptedPrincipalArns parameters accept a list of strings. Also, you can add descriptions to the schema, or restrict allowed values to be a
subset of pre-defined values, using enumerated types (enums).
{ "Version": "2012-10-17", "Statement": [ { "Sid": "CTMULTISERVICEPV1", "Effect": "Deny", "NotAction": [ {{ExemptedActions}} ... "s3:CreateMultiRegionAccessPoint", "s3:DeleteMultiRegionAccessPoint", "s3:DescribeMultiRegionAccessPointOperation", "s3:GetAccountPublicAccessBlock", "s3:GetBucketLocation" ... ], "Resource": "*", "Condition": { "StringNotEquals": { "aws:RequestedRegion": {{AllowedRegions}} }, "ArnNotLike": { "aws:PrincipalARN": [ "arn:aws:iam::*:role/AWSControlTowerExecution", {{ExemptedPrincipalARNs}} ] } } } ] }
The following example shows a full SCP artifact for the control. It shows the actions and principals that are exempted by default when you apply this control to an OU. Remember that AllowedRegions is a mandatory parameter for this control. You can view the most recent version of this SCP in the AWS Control Tower console.
{ "Version": "2012-10-17", "Statement": [ { "Sid": "CTMULTISERVICEPV1", "Effect": "Deny", "NotAction": [ {{ExemptedActions}} "a4b:*", "access-analyzer:*", "account:*", "acm:*", "activate:*", "artifact:*", "aws-marketplace-management:*", "aws-marketplace:*", "aws-portal:*", "billing:*", "billingconductor:*", "budgets:*", "ce:*", "chatbot:*", "chime:*", "cloudfront:*", "cloudtrail:LookupEvents", "compute-optimizer:*", "config:*", "consoleapp:*", "consolidatedbilling:*", "cur:*", "datapipeline:GetAccountLimits", "devicefarm:*", "directconnect:*", "ec2:DescribeRegions", "ec2:DescribeTransitGateways", "ec2:DescribeVpnGateways", "ecr-public:*", "fms:*", "freetier:*", "globalaccelerator:*", "health:*", "iam:*", "importexport:*", "invoicing:*", "iq:*", "kms:*", "license-manager:ListReceivedLicenses", "lightsail:Get*", "mobileanalytics:*", "networkmanager:*", "notifications-contacts:*", "notifications:*", "organizations:*", "payments:*", "pricing:*", "quicksight:DescribeAccountSubscription", "resource-explorer-2:*", "route53-recovery-cluster:*", "route53-recovery-control-config:*", "route53-recovery-readiness:*", "route53:*", "route53domains:*", "s3:CreateMultiRegionAccessPoint", "s3:DeleteMultiRegionAccessPoint", "s3:DescribeMultiRegionAccessPointOperation", "s3:GetAccountPublicAccessBlock", "s3:GetBucketLocation", "s3:GetBucketPolicyStatus", "s3:GetBucketPublicAccessBlock", "s3:GetMultiRegionAccessPoint", "s3:GetMultiRegionAccessPointPolicy", "s3:GetMultiRegionAccessPointPolicyStatus", "s3:GetStorageLensConfiguration", "s3:GetStorageLensDashboard", "s3:ListAllMyBuckets", "s3:ListMultiRegionAccessPoints", "s3:ListStorageLensConfigurations", "s3:PutAccountPublicAccessBlock", "s3:PutMultiRegionAccessPointPolicy", "savingsplans:*", "shield:*", "sso:*", "sts:*", "support:*", "supportapp:*", "supportplans:*", "sustainability:*", "tag:GetResources", "tax:*", "trustedadvisor:*", "vendor-insights:ListEntitledSecurityProfiles", "waf-regional:*", "waf:*", "wafv2:*" ], "Resource": "*", "Condition": { "StringNotEquals": { "aws:RequestedRegion": {{AllowedRegions}} }, "ArnNotLike": { "aws:PrincipalARN": [ {{ExemptedPrincipalArns}} "arn:*:iam::*:role/AWSControlTowerExecution", "arn:*:iam::*:role/aws-controltower-ConfigRecorderRole", "arn:*:iam::*:role/aws-controltower-ForwardSnsNotificationRole", "arn:*:iam::*:role/AWSControlTower_VPCFlowLogsRole" ] } } } ] }
