Mandatory access control (MAC) is a security strategy that restricts the ability individual resource owners have to grant or deny access to resource objects in a file system. MAC criteria are defined by the system administrator, strictly enforced by the operating system (OS) or security kernel, and are unable to be altered by end users.
Often employed in government and military facilities, mandatory access control works by assigning a classification label to each file system object. Classifications include confidential, secret and top secret. Each user and device on the system is assigned a similar classification and clearance level. When a person or device tries to access a specific resource, the OS or security kernel will check the entity's credentials to determine whether access will be granted. While it is the most secure access control setting available, MAC requires careful planning and continuous monitoring to keep all resource objects' and users' classifications up to date.
As the highest level of access control, MAC can be contrasted with lower-level discretionary access control (DAC), which allows individual resource owners to make their own policies and assign security controls.
TheJonDarc explains how MAC works.
See also: role-based access
How do mandatory access control and application sandboxing differ?