I have multi-account AWS environment (set up using AWS Landing Zone) and I need to copy a specific security group to all the accounts. I do have a CFT written, but it's too much of a repetitive task to do this one by one.
The security group is in the central (shared-services) account, which has access to all the other accounts. It's better if there's a way to integrate this to Account Vending Machine (AVM) in order to avoid future tasks of exporting the SG to newly spawned accounts.
You should use CloudFormation Stacksets. StackSets is a feature of cloudformation in which you have a master account in which you create/update/remove the stackset, and you have children accounts. In the stackset, you configure your children aws accounts you want to deploy the CF template and the region as well.
From your comment, your master account is going to be the shared-services and the rest of your accounts, the children ones. You will need to deploy a couple of IAM roles to allow cross-account access, but after that, you will be able to deploy all your templates in up to 500 aws accounts automatically and update them as well.
More information here: https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/what-is-cfnstacksets.html