Confused deputy prevention

The confused deputy problem is a security issue where an entity that doesn't have permission to perform an action can coerce a more-privileged entity to perform the action. In AWS, cross-service impersonation can result in the confused deputy problem. Cross-service impersonation can occur when one service (the calling service) calls another service (the called service). The calling service can be manipulated to use its permissions to act on another customer's resources in a way it should not otherwise have permission to access. To prevent this, AWS provides tools that help you protect your data for all services with service principals that have been given access to resources in your account.

We recommend using the aws:SourceArn, aws:SourceAccount, aws:SourceOrgID, and aws:SourceOrgPaths global condition context keys in resource policies to limit the permissions that gives another service to the resource. Use aws:SourceArn to associate only one resource with cross-service access. Use aws:SourceAccount to let any resource in that account be associated with the cross-service use. Use aws:SourceOrgID to allow any resource from any account within an organization be associated with the cross-service use. Use aws:SourceOrgPaths to associate any resource from accounts within an AWS Organizations path with the cross-service use. For more information about using and understanding paths, see Understand the AWS Organizations entity path.

The most effective way to protect against the confused deputy problem is to use the aws:SourceArn global condition context key with the full ARN of the resource. If you don't know the full ARN of the resource or if you are specifying multiple resources, use the aws:SourceArn global context condition key with wildcard characters (*) for the unknown portions of the ARN. For example, arn:aws:servicename:*:123456789012:*.

If the aws:SourceArn value does not contain the account ID, such as an Amazon S3 bucket ARN, you must use both aws:SourceAccount and aws:SourceArn to limit permissions.

To protect against the confused deputy problem at scale, use the aws:SourceOrgID or aws:SourceOrgPaths global condition context key with the organization ID or organization path of the resource in your resource-based policies. Policies that include the aws:SourceOrgID or aws:SourceOrgPaths key will automatically include the correct accounts and you don't have to manually update the policies when you add, remove, or move accounts in your organization.

The policies documented for granting access to CloudWatch Logs to write data to Kinesis Data Streams and Firehose in Step 1: Create a destination and Step 2: Create a destination show how you can use the aws:SourceArn global condition context key to help prevent the confused deputy problem.