The Mendix platform itself is checked at a regular interval. See also here: https://www.mendix.com/evaluation-guide/enterprise-capabilities/security/

But as  a developer you can still make security mistakes. Those can be found with Javascript or with tools like the security inspector: https://marketplace.mendix.com/link/component/106594 which helps the developer to make sure that only data is exposed to the persons with the right user roles etc.

Regards,

Ronald