An ACL is a set of rules that says which users, services, or roles can use specific commands or reach specific data. In practice, an ACL can be as simple as allowing read-only access, or as strict as permitting only a small list of administrative actions. In Redis and other infrastructure tools, ACLs help separate routine application traffic from powerful operations such as configuration changes, key access, or command execution.
ACLs matter because many attacks succeed only after an attacker gets some level of valid access. If permissions are too broad, a stolen credential or compromised service account can reach dangerous command paths and turn a limited breach into full compromise. Defenders use ACLs to follow least privilege, reduce exposed commands, and contain mistakes in apps and integrations. Strong ACLs are most effective when combined with network segmentation, strong authentication, and careful review of which commands each account can run.