Definition
An access control list, or ACL, is a set of rules attached to an object that defines which users or systems are granted access to that object and what actions they can perform. These rules specify permissions, such as read, write, or execute, for specific subjects like user accounts or groups. ACLs are fundamental to enforcing security policies by dictating access privileges to resources like files, network devices, or databases. For instance, an ACL on a shared folder might permit only the accounting department to modify its contents, while others can only view it. Unlike a firewall rule that filters traffic, an ACL governs permissions on the resource itself. This concept is a core component of cybersecurity certifications like CompTIA Security+, CySA+, and CISSP.