What is a best practice regarding the order of rules in an Access Control List (ACL)?

The recommended best practice when configuring an Access Control List (ACL) is to place specific rules at the top and more generic rules at the bottom. This approach is essential because ACLs are processed in a sequential manner; once a match is found, that rule is applied, and further rules are not evaluated. Therefore, placing specific rules first ensures that specialized conditions are addressed before the broader, more inclusive rules are assessed.

By structuring the ACL in this manner, you minimize the risk of unintended access being granted by a generic rule that might overlap with a specific use case. For example, if a specific rule allows access to a particular resource for a certain user and a more generic rule follows that allows broader access to that resource, the specific rule must take precedence to ensure that the user is prioritized according to the defined security requirements.

Thus, placing specific rules at the top helps maintain tighter control and security, ensuring that the intended access policies are enforced correctly.