MariaDB security on Amazon RDS
Security for MariaDB DB instances is managed at three levels:
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Amazon Identity and Access Management controls who can perform Amazon RDS management actions on DB instances. When you connect to Amazon using IAM credentials, your IAM account must have IAM policies that grant the permissions required to perform Amazon RDS management operations. For more information, see Identity and access management for Amazon RDS.
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When you create a DB instance, you use a VPC security group to control which devices and Amazon EC2 instances can open connections to the endpoint and port of the DB instance. These connections can be made using Secure Socket Layer (SSL) and Transport Layer Security (TLS). In addition, firewall rules at your company can control whether devices running at your company can open connections to the DB instance.
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Once a connection has been opened to a MariaDB DB instance, authentication of the login and permissions are applied the same way as in a stand-alone instance of MariaDB. Commands such as
CREATE USER,RENAME USER,GRANT,REVOKE, andSET PASSWORDwork just as they do in stand-alone databases, as does directly modifying database schema tables. 
When you create an Amazon RDS DB instance, the master user has the following default privileges:
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alter - 
            
alter routine - 
            
create - 
            
create routine - 
            
create temporary tables - 
            
create user - 
            
create view - 
            
delete - 
            
drop - 
            
event - 
            
execute - 
            
grant option - 
            
index - 
            
insert - 
            
lock tables - 
            
process - 
            
references - 
            
reloadThis privilege is limited on MariaDB DB instances. It doesn't grant access to the
FLUSH LOGSorFLUSH TABLES WITH READ LOCKoperations. - 
            
replication client - 
            
replication slave - 
            
select - 
            
show create routineThis privilege is only on MariaDB DB instances running version 11.4 and higher.
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show databases - 
            
show view - 
            
trigger - 
            
update 
For more information about these privileges, see User account management
Note
Although you can delete the master user on a DB instance, we don't recommend
            doing so. To recreate the master user, use the
            ModifyDBInstance API or the
            modify-db-instance Amazon CLI and specify a
            new master user password with the appropriate parameter. If the master user does
            not exist in the instance, the master user is created with the specified
            password. 
To provide management services for each DB instance, the rdsadmin
        user is created when the DB instance is created. Attempting to drop, rename, change
        the password for, or change privileges for the rdsadmin account results
        in an error.
To allow management of the DB instance, the standard kill and
        kill_query commands have been restricted. The Amazon RDS
        commands mysql.rds_kill,
        mysql.rds_kill_query, and
        mysql.rds_kill_query_id are provided for use in MariaDB and
        also MySQL so that you can end user sessions or queries on DB instances.