What is an access control list (ACL)?

An access control list (ACL) is fundamentally a table of access rules that defines the permissions granted to various users or groups for specific resources within a computer system or network. This mechanism is critical for implementing security policies, as it establishes who can access what resources and under what conditions they can do so. Each entry in the ACL specifies which users or groups have permission to access a resource and what level of access (such as read, write, or execute) they have.

In the context of cybersecurity, ACLs are essential for protecting sensitive data and ensuring that only authorized individuals can interact with certain files, directories, or network services. This helps prevent unauthorized access and potential breaches, enabling organizations to maintain tighter control over their information systems. ACLs can be applied at various levels—such as files, directories, network devices, or even applications—making them a versatile tool in the broader framework of access management and security policies.