Access Control List (ACL)

Security+ šŸ† ā€¢ Network Security šŸŒ ā€¢ Difficulty: free

Definition

An ACL is an ordered set of allow/deny rules that decides which identities or traffic can access a resource. ACLs are used on routers, firewalls, operating systems, cloud resources, and applications to enforce least privilege.

Examples

  • A router inbound ACL only permits TCP 443 from the web tier to an API subnet; all other traffic is denied.
  • A Linux file ACL grants a QA group read-only access to logs while admins have full control.

Discover šŸ”Ž

ACLs are the simplest and most common way to enforce access. They evaluate requests against a list of rulesā€”from top to bottomā€”and either permit or deny. Because ACLs sit close to the resource (a network interface, a file, a bucket, an API), they provide fast, deterministic control and a clear audit surface when paired with logging.

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