Whitelisting, often called an “allow list,” is a security approach where access is granted only toexplicitly approvedidentities, services, applications, IP addresses, domains, or network flows. In network security, this means the default stance is “deny by default,” and only pre-authorized entities are allowed to communicate or use specific resources. Option C matches this definition because it describes the core idea: explicitly permitting known, approved subjects (people, groups, service accounts, systems) to access a defined privilege or service.
Cybersecurity documents emphasize whitelisting as a strong risk-reduction technique because it constrains the attack surface. Instead of trying to block every bad thing (which is difficult due to evolving threats), whitelisting focuses on allowing only what is required for business operations. Examples include firewall rules that only permit specific source IPs to reach an admin interface, network segmentation policies that allow only required ports between zones, and application whitelisting that permits only approved executables to run. When implemented correctly, it reduces lateral movement opportunities, limits command-and-control traffic, and prevents unauthorized tools from executing.
Whitelisting is different from segmentation (option A), which is about isolating zones based on security needs, and different from blacklisting (option B), which blocks known-bad items. It is also not malware scanning (option D), which detects malicious code after it appears. Whitelisting aligns with least privilege and zero trust principles by tightly controlling what is allowed.
