Which type of security measure allows the definition of what is permitted to run on a system?

The correct answer is an allow list. An allow list is a security measure that specifies which applications, services, or processes are permitted to execute on a system. By default, everything else is denied, meaning that only the items explicitly included in the allow list can run. This approach helps to significantly reduce the attack surface and limit the potential for unauthorized or malicious activities.

Using an allow list enhances security by ensuring that only known and trusted applications can operate, making it a vital component of proactive security strategies, particularly in environments where risk management is critical. This method contrasts with other security approaches that rely on the identification of threats or the blocking of specific unwanted entities, which may not be as effective in preventing new or unknown threats.

In environments where control over what is executed is paramount, an allow list is particularly effective, ensuring comprehensive oversight of the system's operational parameters while reducing reliance on reactive measures.