We are excited to announce that you can now reference security groups in a peered Virtual Private Cloud (VPC) in both inbound and outbound rules. This functionality is supported cross-account so the two VPCs can be in different accounts. Support for security group references in a peered VPC simplifies configuration by controlling peering traffic via security group membership instead of CIDR ranges.
You can reference security group from a peered VPC using the AWS Management Console,AWS CLI, through SDKs. For more information see ‘Reference Peered VPC Security Groups’.
Source: amazon.com