What should be implemented?

Full-disk encryption secures data at rest by encrypting the entire hard drive, making it inaccessible without the proper credentials. While important for data protection, it does not address the risks associated with unsafe input data being processed by applications. This means that without input validation, malicious data could still compromise the system, regardless of encryption measures.

A VPN (Virtual Private Network) provides a secure connection over the internet by encrypting data in transit. However, it does not safeguard against the dangers posed by invalid or malicious inputs received by an application. As such, a VPN is more about securing data transmission rather than ensuring that the data being processed is safe and valid.

Firewalls act as barriers between trusted internal networks and untrusted external networks, filtering traffic based on predetermined security rules. While they are essential for network security, they do not inherently validate the data being processed by applications. Thus, without input validation, firewalls alone cannot prevent attacks that exploit vulnerabilities in application input handling.