An Access Control List (ACL) is a set of rules used to grant or deny access to digital environments.
ACLs are a fundamental security mechanism employed across various computing contexts, from file systems and network devices to applications and databases. Their primary purpose is to define permissions, specifying who or what can access a particular resource and what actions they are allowed to perform.
Understanding ACLs
According to Imperva, an access control list (ACL) contains rules that grant or deny access to certain digital environments. Think of an ACL as a guest list or a security checkpoint for digital resources. Each rule in the list typically consists of:
- An identifier: The entity (user, group, process) requesting access.
- A resource: The digital object (file, directory, network port, database record) being accessed.
- Permissions: The actions (read, write, execute, delete, allow, deny) that the entity is allowed or denied on the resource.
When an entity attempts to access a resource protected by an ACL, the system checks the rules in the list. It searches for a rule that matches the requesting entity and the target resource. Based on the permissions defined in the matching rule (or the most specific matching rule), the access attempt is either granted or denied.
Types of ACLs
While ACLs are used in many areas, they are commonly encountered in two primary domains: Filesystems and Networks. The provided reference specifically mentions Filesystem ACLs.
Filesystem ACLs
The reference states, "There are two types of ACLs: Filesystem ACLsâfilter access to files and/or directories."
Filesystem ACLs are integral to operating systems like Windows and Linux. They go beyond traditional file permissions (like the owner, group, and others permissions in Linux) to offer more granular control.
Filesystem ACLs tell operating systems which users can access the system, and what privileges the users are allowed. This means you can specify permissions for individual users or groups on specific files or folders, defining exactly who can read, write, execute, or modify those resources.
Examples of what Filesystem ACLs manage:
- Allowing a specific user, who is not the owner or in the file's group, to write to a file.
- Denying a particular group access to a sensitive directory, even if broader permissions might otherwise allow it.
- Setting default permissions for new files created within a specific directory.
Filesystem ACLs provide flexibility and precision in managing access rights within an operating system's file hierarchy.
For more information on Access Control Lists, you can refer to the original source: What is Access Control List | ACL Types & Linux vs Windows - Imperva.
