Access Control List (ACL) in cyber security: Beneficial for all, critical for some

For IT leaders, balancing security and usability is a constant challenge. Access Control Lists (ACLs) offer a way to manage access to critical resources to protect them from bad actors. ACLs can be considered cyber security basics, but they do also come with a few drawbacks. 

It’s also a cyber security measure that’s more critical to some companies than others. Explore when ACLs work best, where they might fall short, and how they fit into a broader security strategy, including what industries benefit the most from ACLs. 

This article covers:


What is an Access Control List (ACL)?

An Access Control List (ACL) is a security mechanism that controls access to data and resources. It specifies which users or systems are granted or denied access to specific network resources. ACLs are typically configured at the endpoint level, such as on routers, servers, or laptops, so only authorised entities can access particular devices or data.

Access Control Lists can be distinguished into “allow” and “deny” lists. An allow list grants access to explicitly mentioned entities, ensuring that only those listed can access the resources. In contrast, a deny list permits access to everyone except those explicitly excluded. This system effectively manages and restricts access, enhancing security by defining precise permissions.


What are ACLs used for?

Access Control Lists (ACLs) manage and control access to network resources and data. They specify which users or systems are allowed or denied access to particular resources. For example, your company might use an ACL to restrict access to a testing server, allowing only developers to access it based on their IP or MAC addresses.

Additionally, ACLs are often used in firewalls and other network devices to enhance security. They can block known malicious IP addresses and hacker groups, preventing unauthorised access and potential attacks.


ACLs as the first line of defence in cyber security

Access Control List is one of the cyber security measures that’s a no-brainer: everybody needs it, and almost everybody uses it. ACLs serve as the first line of defence in cyber security for many companies, probably also yours.

By configuring ACLs, you can control which users or systems can access specific data or network segments. This basic yet powerful approach helps to set up defences quickly. And most devices, such as Windows servers, come with built-in ACL capabilities, making them easy to implement.


However, ACLs can become cumbersome as your company grows. Managing access for a large number of employees, especially when using VPNs that obscure IP addresses, can be complex and challenging. While ACLs are great for quick, initial setups, bigger organisations might need to transition to more scalable solutions like role-based access controls (RBAC).


How does ACL compare with Role-Based (RBAC), Attribute-Based (ABAC) and Discretionary Access Control (DAC)?

Access Control Lists (ACLs), Role-Based Access Control (RBAC), and Attribute-Based Access Control (ABAC) and Discretionary Access Control (DAC) each have their benefits and challenges. Here’s how they compare.

Access Control Lists (ACLs)

ACLs manage access by specifying which users or devices can access specific resources. This method is straightforward and effective for smaller organisations. However, keeping ACLs updated can become time-consuming and complex as your organisation grows.

Role-Based Access Control (RBAC)

RBAC assigns permissions based on user roles within the organisation. You group users by roles like admin, editor, or viewer, making managing access for larger teams easier. The downside is that if you need detailed permissions, too many roles can make things complicated.

Watch video: New cyber threats: your voice is my password

Attribute-Based Access Control (ABAC)

ABAC uses attributes such as time, location, and device type to control access. This approach allows for very specific and customisable policies. While ABAC provides flexibility, it requires detailed planning and ongoing management, making it more complex to implement compared to ACLs and RBAC.

Discretionary Access Control (DAC)

DAC allows resource owners to decide who can access their resources. This method provides a high level of flexibility and control for data owners but can lead to inconsistent security policies if not managed carefully. DAC is easy to implement in small environments but becomes cumbersome in larger, more dynamic organisations.


ACLs within the CIA triad

Access Control Lists (ACLs) support the entirety of the CIA triad: Confidentiality, Integrity, and Availability. For confidentiality, you use ACLs to restrict data access to authorised users only. This way, sensitive information stays protected from unauthorised access.

To maintain integrity, ACLs control who can modify data. By allowing only specific users to make changes, you ensure that data remains accurate and trustworthy.

For availability, ACLs help prevent Distributed Denial of Service (DDoS) attacks. By blocking unregistered IP addresses, ACLs stop malicious traffic before it can disrupt your system. This keeps your resources accessible to legitimate users.


Why ACLs are more critical to some companies than others

Access Control Lists (ACLs) are critical in several scenarios. One example is blocking darknet attacks. You can use cyber security tools to get daily updates of known malicious IP addresses linked to the darknet and add these to your ACLs. This denies access from these sources and protects your network.


Another example is data protection. Use ACLs to ensure only specific individuals can access sensitive information, such as personally identifiable information (PII). This helps maintain data confidentiality and meet compliance requirements. By restricting access to a small, necessary group, you provide a straightforward way to secure sensitive data.

Because of this, ACLs are also more critical to some companies than others, especially those with strict compliance requirements.

FinTech and E-commerce

Finance and e-commerce companies handling credit card transactions must adhere to PCI DSS standards, which mandate access controls. By using ACLs, you can segregate and secure sensitive areas of the network, ensuring only authorised personnel access critical data. This compliance helps avoid fines associated with data breaches and non-compliance.

Professional services

Professional services companies might find ACLs less critical but still use them to manage access to client information and internal documents. For example, platforms like SharePoint use ACLs to control document access. By setting up ACLs, you maintain a baseline level of security, controlling who can access specific documents and data, even if your requirements are not as stringent as those in finance or healthcare.

Read more: What are some examples of cyber security measures for professional services?

Healthcare industry

Healthcare organisations rely on ACLs to maintain access controls for patient records, which must be protected under regulations like HIPAA. By setting up ACLs, you ensure that only specific healthcare professionals, such as assigned doctors, can access patient records. This segregation of access prevents unauthorised access and maintains patient confidentiality.


The most common pitfalls organisations face when implementing ACLs

Implementing Access Control Lists (ACLs) secures network resources, but organisations often face several challenges.

Documentation and maintenance

Keeping ACLs updated can be a headache. You need to track who has access to what, which can be time-consuming and error-prone. Without accurate documentation, updating ACLs as your organisation grows can lead to security gaps.

Proving effectiveness

It can be challenging to prove that ACLs work as intended. Regular log reviews are needed to prove their effectiveness. This process takes time and expertise; without clear evidence, it's hard to justify keeping ACLs. Setting up a sound monitoring system can help solve this problem.

Training and user frustration

Training staff on ACLs is essential to prevent access issues. Employees may face problems accessing shared files, leading to frustration and inefficiency. Teaching employees how to use ACLs correctly can reduce these issues, but it requires ongoing support and education.


How to make sure your ACLs are effective?

To ensure Access Control Lists (ACLs) remain effective, follow the Plan-Do-Check-Act (PDCA) cycle. Start by planning and implementing ACLs based on your security policies and procedures. Regularly review and update these lists to reflect changes in personnel or access requirements. For small companies, check ACLs weekly or monthly and after any security incidents. Document all changes and keep clear records of who has access to what resources.

Conduct regular audits and tests to ensure ACLs work as intended. Use a non-authorised laptop to try accessing restricted resources and record the results. Regularly update your ACLs, possibly using automated tools, to handle growth and complexity. Educate all staff, not just IT personnel, about ACLs and the procedures for requesting access.


How do ACLs integrate with other security measures and technologies?

Access Control Lists (ACLs) integrate with other security measures and technologies to enhance overall security. For example, you can use ACLs to protect servers containing encryption keys. By restricting access to these keys, you add an extra layer of authentication, ensuring that only authorised users can access the encrypted data. This integration supports a multi-layered security approach where ACLs work alongside encryption to safeguard sensitive information.

ACLs also complement other security measures like multi-factor authentication (MFA). While ACLs control access based on user identity and device, MFA adds another layer of verification, reducing the risk of unauthorised access due to phishing attacks or compromised credentials. By implementing ACLs with MFA, you create a robust security framework that verifies user identity through multiple checks, ensuring that only legitimate users can access critical resources.

Can you overuse ACLs?

As your company grows, you might continue relying heavily on ACLs because your IT team is familiar with them. However, overly strict ACLs can create access problems. If certain people can't access the data they need, it impacts availability, a key aspect of cyber security. Misconfigured ACLs can block necessary access, causing operational delays and inefficiencies.

To avoid these problems, balance your use of ACLs. Don't restrict access too much, as it can introduce new risks. Ensure your ACLs are correctly configured to allow necessary access while still protecting sensitive data. Regularly review and adjust ACLs to align with changing roles and access needs within the company.

How to keep your company compliant and secure

ACL is just one part of the cyber security puzzle. If you know your critical assets and risks well, you can build a strong security base to fight off or mitigate any emerging cyber threats, all while remaining compliant.

Start by targeting your most significant risks first and go from there. For that, use an all-in-one security platform to manage your ISMS and build a thorough overview of your most pressing risks and assets. And if you could use some help on the way – we’re here for you:



Frequently Asked Questions

What is the difference between an ACL and a firewall?

An Access Control List (ACL) is a set of rules used to permit or deny traffic to a network resource based on IP addresses and ports. It operates at the network layer and is used primarily to control traffic flow within a network. A firewall, on the other hand, is a more comprehensive security device that monitors and filters incoming and outgoing traffic based on a predefined set of security rules. Firewalls can operate at multiple layers of the OSI model and provide a broader range of protections, including packet filtering, stateful inspection, and application-layer filtering.

How do I view an access control list?

To view an access control list, you typically need administrative access to the network device where the ACL is configured. For example, on a Cisco router, you can view the ACL by accessing the device via command-line interface (CLI) and entering the command to show access-lists. This command will display all the configured ACLs and their rules, allowing you to review and manage the access control settings.

What is the most common access control list?

The most common access control list is the Standard ACL. Standard ACLs are widely used because they are straightforward to implement and manage. They focus on filtering traffic based on the source IP address, making them suitable for simple network environments where fine-grained traffic control is not required.

What does an access control list block?

An access control list (ACL) blocks or allows traffic based on predefined rules set by network administrators. These rules specify which IP addresses, protocols, and ports are permitted or denied access to network resources. By evaluating the headers of incoming and outgoing packets, an ACL can block unauthorized access to sensitive data and systems, enhancing the security of the network.

Where should a standard access control list be placed?

A standard access control list (ACL) should be placed as close as possible to the source of the traffic that needs to be controlled. This placement minimizes unnecessary traffic on the network by filtering packets before they traverse extensive parts of the network infrastructure. This strategy helps reduce bandwidth usage and processing load on downstream devices, ensuring efficient and secure network operations.

What is access control list in network security?

An access control list (ACL) in network security is a set of rules that govern the inbound and outbound traffic on a network. These rules are used to control which users or systems can access network resources, thereby enhancing security by preventing unauthorized access. ACLs can be applied to routers, switches, and firewalls, and they are essential for implementing network security policies, ensuring that only legitimate traffic is allowed while blocking potentially harmful activities.

About the author

Emrick Etheridge Emrick Etheridge
Emrick Etheridge

Emrick Etheridge is an associate Information Security Consultant and a certified ISO 27001 Lead Auditor. Prior to DataGuard, Emrick studied Computer Science at Anglia Ruskin University (Cambridge) before entering a world of Digital Forensics and Information Security for a Cambridge based company. In these roles, he consulted merchants who required either a digital forensic investigation or re-certification. Emrick was also a certified Cyber Essentials assessor at the heart of the pandemic which proved to be an interesting time in industry. In his current role, he helps SMEs create an Information Security Management System (ISMS) to strengthen their security posture as well as consulting them on their path to obtaining ISO 27001 certification.

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