Amazon RDS now supports MySQL Community Edition minor versions 5.7.25 and 5.7.24, and MariaDB minor version 10.2.21 in all AWS regions. These new minor versions include functionality improvements and fixes.
Refer the release notes for details:
Get started by launching a new Amazon RDS database instance or upgrading your current instance with just a few clicks in the AWS Management Console. Learn more about upgrading your database instances from the Amazon RDS User Guide.