Understanding ServiceNow ACL: A Guide for Admins and Developers

[BillMartin]

In ServiceNow, access control is a crucial aspect of maintaining data security and ensuring that users can only interact with the information they are authorized to access. This is where ServiceNow Access Control Lists (ACLs) come into play. For administrators and developers working with ServiceNow, having a deep understanding of ACLs is essential for building secure, scalable, and efficient systems.

This article will walk through the basics of ServiceNow ACLs, their structure, how to create and manage them, and best practices for admins and developers.

What is an ACL in ServiceNow?

An Access Control List (ACL) in ServiceNow is a security rule that controls access to data in the platform. ACLs define which users or roles have permission to perform actions such as reading, writing, or deleting records on tables or fields. By using ACLs, admins and developers can finely control who sees what and who can modify data across the platform.

Each ACL rule in ServiceNow contains specific permissions based on:

• Object Type (e.g., table, field, or record)
• Operation (e.g., create, read, write, delete)
• Condition (optional, to further define when the ACL applies)
• Script (for more advanced logic)

How ServiceNow ACLs Work

ServiceNow evaluates ACLs in a hierarchical and dynamic manner. When a user attempts to access a record or field, ServiceNow checks the ACL rules that apply to the requested object. Each ACL rule corresponds to a specific operation, and ServiceNow evaluates the most specific rules first.

The general evaluation process is as follows:

1. Table-Level ACLs: These rules control access to the entire table and are evaluated first.
2. Field-Level ACLs: If table-level access is granted, field-level ACLs are checked next. These rules allow more granular control over specific fields within the table.
3. Advanced Script Logic: If a script is defined in the ACL, it is executed and must return true for access to be granted.

ServiceNow ACL Rule Structure

An ACL rule has several key components:

• Type: Defines whether the rule applies to a table, field, or UI element.
• Operation: Specifies the action being controlled (create, read, write, delete).
• Condition: An optional condition that must be met before the rule is applied. This can be based on values from the record being accessed.
• Script: A JavaScript script that returns true or false to grant or deny access. This is where custom logic can be added.

For example, a read ACL might be written for the Incident table that allows users to read the record only if they are the caller of the incident or part of a specific user group.

 

Creating and Managing ACLs in ServiceNow

 

Creating ACL Rules

To create an ACL in ServiceNow:

1. Elevate your role to security admin
2. Navigate to System Security > Access Control (ACL) in the application navigator.
3. Click New to create a new ACL rule.
4. Define the following fields:
   • Type: Choose whether the rule is for a table or a field.
   • Operation: Specify the operation (create, read, write, or delete).
   • Name: Select the table or field the ACL applies to.
   • Condition: (Optional) Add a condition if necessary.
   • Script: Add any advanced logic here.
5. Click Submit to save the rule.

 

Best Practices for Managing ACLs

1. Use Roles Effectively

Roles are the foundation of access control in ServiceNow. Always assign roles based on least privilege, ensuring users have only the permissions they need. When creating ACLs, consider how roles align with the organization’s security policies, and group ACLs by roles to avoid redundancy.

2. Combine Conditions and Scripts

Use a combination of conditions and scripts to refine ACLs. Conditions are easier to manage and read, while scripts provide the flexibility for more complex logic. Try to minimize the complexity of ACL scripts, as they can slow down system performance if overused.

3. Test ACLs in a Development Environment

Before applying ACLs to production, always test them in a development or test environment. Ensure that the correct users can access the data they need, and no unauthorized access is permitted.

4. Document Your ACLs

Given the complexity of ServiceNow ACLs, it’s important to document them thoroughly. Document the purpose, conditions, and roles associated with each ACL. This is especially helpful when onboarding new admins or developers, or when revisiting older ACLs during system audits.

5. Use Field-Level ACLs Sparingly

Field-level ACLs are useful but can quickly become difficult to manage at scale. Use them only when absolutely necessary, such as when you need to protect sensitive information in specific fields. Rely on table-level ACLs for broader access control whenever possible.

Debugging ACLs in ServiceNow

ServiceNow provides tools to help debug ACL rules, which can be incredibly helpful for admins and developers when troubleshooting access issues.

• Security Debugging: Use the Debug Security Rules feature to trace how ACLs are evaluated for a particular user. This tool provides insights into which rules are being applied and why access is being granted or denied.
• Test ACL: You can also test an ACL directly from the ACL record to ensure it is working as expected.

To enable Debug Security Rules, navigate to the user profile and click Debug Security Rules. Once activated, try accessing a record, and the debug window will show which ACLs were evaluated and the outcomes.

Common Pitfalls to Avoid

• Overlapping ACLs: Having multiple ACLs for the same table or field can cause confusion and unintended access issues. Always ensure that your ACLs are unique and specific to avoid conflicts.
• Granting Broad Access by Default: Avoid granting overly broad access through roles or ACLs unless absolutely necessary. Broad access can expose sensitive information and reduce the system’s overall security.
• Not Testing All Scenarios: When testing ACLs, consider all possible user roles, groups, and record conditions. Missing a single scenario can lead to gaps in security.

 

Conclusion

ServiceNow ACLs are a powerful mechanism for securing data and ensuring that only authorized users can access or modify records. For admins and developers, understanding how ACLs work, along with implementing best practices for creating and managing them, is essential for building a secure and efficient system.

By carefully designing ACLs, leveraging roles, and combining conditions and scripts, you can create a well-structured access control system that meets the needs of the organization while maintaining high security standards. Regular testing and documentation are key to maintaining the effectiveness and clarity of ACL rules over time.

If you're looking for a more in-depth walkthrough on how to implement and manage ACLs in ServiceNow, be sure to watch my video tutorial. In the video, I break down the key concepts and walk you through real-world examples to help you master ACLs with confidence. Don’t miss it—click here to watch now and level up your ServiceNow skills!

[Mark Manders]

Next to that all the capitals in the middle of sentences makes it hard to read the article, I am also missing the newly introduced functionality of 'deny-unless' ACL's and the 'applies_to' field that both have been introduced in Xanadu. These changes can have a huge impact on the way you secure your data if applied correctly. No need for exceptions, just use the 'deny-unless' ACL. 
Thanks for sharing! With an addition of these two things, it's a very nice article to bookmark as reference in relation to ACLs.

[BillMartin · Accepted solution]

hi @Mark Manders , 

Thank you for your valuable insights and the effort you put into enhancing the quality of the post.

[Nikhil Bajaj9]

Hi Bill,

You are marking all your Answers as Solution Accepted. Great :). Solution accepted facility is given so that you can mark any answer which is correct.

Regards,

Nikhil Bajaj

[Mark Manders]

What is your point exactly? 

Since it's not possible for many users to post blogs or articles, but just questions, sharing knowledge needs to be done through the question part of the community. By marking a (or any) reply as 'correct' you enable others to find your contribution when they are looking for 'solved' issues and help them with their issue.