What is essential for blocking unauthorized applications from running on virtual machines?

Application whitelisting controls are crucial for preventing unauthorized applications from running on virtual machines because they establish a security framework that explicitly allows only approved applications to execute. By using whitelisting, organizations can define a list of trusted software, which minimizes the risk of malware and unauthorized applications gaining access to the environment. This proactive measure is particularly effective in virtualized environments, where the risk of running unverified applications is elevated due to multiple instances of virtual machines operating independently.

In contrast, the other options serve different purposes. Azure Firewall policies focus on controlling network traffic, allowing or denying traffic to and from the virtual machines based on predefined rules, but do not specifically address which applications are permitted to run within those machines. Conditional access policies are designed to manage user access to resources based on certain conditions, such as location and device compliance, and are not focused on application control. Azure AD Identity Protection helps identify and respond to identity-related risks but does not directly block or manage applications on virtual machines. Each of these security measures plays a vital role in a broader security strategy, but application whitelisting is the key control specifically designed for blocking unauthorized applications at the application level.