📖 What is Access Control List (ACL)?
Access Control List (ACL) is a table that tells a computer operating system or network device which access rights each user or IP address has to a specific object. It acts as a filter to permit or deny traffic based on defined criteria.
"Pay close attention to the order of rules in an ACL; they are typically processed sequentially from top to bottom until a match is found."
📚 Certification: Certified in Cybersecurity (CC)
🔑 What are the Key Concepts of Access Control List (ACL)?
- ▸ Sequential Processing: Rules are evaluated from top to bottom; once a match is found, the action is taken and no further rules are checked.
- ▸ Implicit Deny: Most ACLs conclude with an invisible 'deny all' rule, ensuring any traffic not explicitly permitted is blocked by default.
- ▸ Network Filtering: Network-based ACLs filter traffic using criteria such as source/destination IP addresses, protocol types, and specific port numbers.
- ▸ Object-Level Permissions: In operating systems, ACLs manage granular access rights, such as read, write, and execute, for specific users or groups on files.
- ▸ Stateless Nature: Many network ACLs are stateless, meaning they do not track connection state and require explicit rules for both inbound and outbound traffic.
🎯 How does Access Control List (ACL) appear on the CC Exam?
You may be asked to troubleshoot a connectivity issue where a 'permit' rule is ignored because a more general 'deny' rule appears higher in the list.
A scenario might describe a security administrator applying the principle of least privilege by configuring an ACL to block all traffic except for essential services.
Expect questions requiring you to distinguish between a network ACL filtering traffic at a router and a file system ACL controlling access to a folder.
❓ Frequently Asked Questions
What is the difference between an ACL and a firewall?
An ACL is a specific list of rules used to filter traffic, while a firewall is the overall security device or software that implements those ACLs among other features.
Why is the 'Implicit Deny' concept important for the exam?
It represents the 'Default Deny' security posture. If a packet doesn't match any rule, it is dropped, preventing unauthorized access by default rather than by exception.
Can an ACL be used for both users and network traffic?
Yes. In a cybersecurity context, ACLs apply to both network layers (filtering IP packets) and system layers (controlling which user accounts can access specific files).