Understanding Access Control Lists (ACLs) in ServiceNow

Access Control Lists (ACLs) are a fundamental security feature in ServiceNow that help administrators control access to data. An ACL defines which users, groups, or roles can access certain resources or perform certain actions in the platform. The resources can include tables, records, fields, and even methods in scripts. ACLs are an essential tool for ensuring that only authorized users can access sensitive information or perform specific tasks.

In this article, we will explore how ACLs work in ServiceNow, types of ACLs you can create, the order in which ACLs are evaluated, and how you can use scripting for complex access control scenarios.

1. What are ACLs in ServiceNow?

An Access Control List in ServiceNow is a set of rules that determines what type of access a user has to a specific resource in the system. This includes read, write, create, and delete permissions. ACLs apply to various resources such as:

• Tables: To control access to entire tables or records.
• Fields: To control access to specific fields in a record.
• Methods: To restrict access to script executions or functions.

2. Types of ACLs in ServiceNow

There are four main types of ACLs that you can configure in ServiceNow:

Table ACLs (Record ACLs)

• These ACLs control access to entire tables or individual records within a table. For example, you may want to limit access to the "Incident" table, allowing only certain roles or groups to view or modify the records.
• Example: You could create an ACL that restricts access to the incident table only to users with the incident_manager role.

Field ACLs

• Field-level ACLs define access to individual fields in a table. For instance, you may allow a user to view a record but restrict access to certain fields like the budget field on a Project record.
• Example: You may create an ACL on the priority field of the incident table, granting read/write access only to users with the admin role.

Scripted ACLs

• These are custom ACLs defined by scripts to apply more complex logic for determining access to records. Scripted ACLs can evaluate conditions based on complex business logic, making them useful for scenarios where the default ACL conditions are not enough.
• Example: A scripted ACL could check if the user is part of the incident_manager group and the incident was created in the last 30 days before granting access.

Method ACLs

• These ACLs are used to control access to ServiceNow's business logic methods or script executions. For example, you might create an ACL to restrict who can execute a specific business rule or access a web service.
• Example: You could create an ACL that allows only users with a developer role to execute a custom script.

3. Order of Evaluation for ACLs

The order in which ACLs are evaluated in ServiceNow follows a specific hierarchy and is crucial to understanding how access is granted or denied. Here’s the basic order of evaluation:

1. Table-level ACL Evaluation: The system first checks for ACLs on the entire table.
2. Record-level ACL Evaluation: After the table ACLs, the system evaluates record-specific ACLs.
3. Field-level ACL Evaluation: Finally, the system checks the field-specific ACLs for any restrictions on individual fields.

The evaluation order is as follows:

• First, the Table ACLs are checked to determine whether the user has the required permissions on the table.
• Then, the Record ACLs are evaluated to determine if the user can access the specific record.
• Finally, the Field ACLs are evaluated for access to individual fields within the record.

It’s important to note that multiple ACLs can be applied to the same resource (e.g., a record or field). The access control rules are combined, and if any ACL denies access, the user will be denied access to that resource.

4. How Scripting Can Be Leveraged in Complex ACL Scenarios

For more complex access control scenarios where predefined ACL rules might not suffice, scripting can be used to create Scripted ACLs. These ACLs allow you to write custom scripts to define the logic that determines whether a user can access a resource.

Here’s a breakdown of how scripting can be used:

• Scripted Table ACLs: You can write a script that checks additional conditions beyond just user roles. For instance, you can check if the record’s creator is the same as the current user before granting access to a record.
• Scripted Field ACLs: Field-level scripts can check values in related tables or external systems to make decisions about whether to allow access to a field.
• Example: In a scripted ACL for the incident table, you could check if the current user has the same department as the assigned_to user or if the user is an admin before granting write access to the incident record.

Example Script for Scripted ACL

This scripted ACL checks whether the current user belongs to the same department as the user assigned to the incident or whether the user has the admin role. If either condition is true, the user is granted access.

5. Diagram: ACL Evaluation Flow

To simplify the understanding of how ACLs are evaluated in ServiceNow, here is a diagram representing the flow:

6. Best Practices for Managing ACLs

When managing ACLs in ServiceNow, it’s crucial to follow best practices to ensure effective and secure access control:

• Use roles efficiently: Always assign the appropriate roles to users rather than individual ACLs to control access.
• Leverage scripting for complex conditions: Use scripted ACLs when the predefined rules are insufficient for your business needs.
• Test your ACLs: Always test the ACLs in a development or testing environment to ensure they work as expected.
• Avoid overly complex ACLs: While scripted ACLs provide flexibility, they can make the system harder to maintain. Use them only when necessary.

Conclusion

Access Control Lists (ACLs) in ServiceNow are a powerful feature for managing data access and security. They help you define who can access what resources within the platform based on roles, groups, and conditions. By understanding the types of ACLs, their evaluation order, and how scripting can be used for complex scenarios, you can create a more secure and flexible access control structure in ServiceNow.

By following best practices and leveraging ACLs correctly, you can ensure that your ServiceNow instance is both secure and easy to maintain.