Yes, Kentico is generally considered to be a safe platform for web application development. The platform is built on the Microsoft .NET framework, which has a strong track record of security and is regularly updated with security patches and updates.
Kentico also includes a range of security features and best practices designed to protect against common web security threats, such as cross-site scripting (XSS) attacks, SQL injection attacks, and cross-site request forgery (CSRF) attacks.