ACL Security Patterns for ServiceNow

Access Control Lists (ACLs) are the foundation of ServiceNow security. They control who can read, write, create, and delete records.

ACL Evaluation Order

ACLs are evaluated in this order (first match wins):

1. Table.field - Most specific (e.g., incident.assignment_group)
2. *Table.` - Table-level field wildcard
3. Table - Table-level record ACL
4. Parent table ACLs - If table extends another
5. * - Global wildcard (catch-all)

ACL Types

Type	Controls	Example
record	Row-level access	Can user see this incident?
field	Field-level access	Can user see assignment_group?
client_callable_script_include	Script Include access	Can user call this API?
ui_page	UI Page access	Can user view this page?
rest_endpoint	REST API access	Can user call this endpoint?

Creating ACLs via MCP

// Table-level READ ACL
snow_create_acl({
  name: "incident",
  operation: "read",
  admin_overrides: true,
  active: true,
  roles: ["itil", "incident_manager"],
  condition: "current.active == true",
  script: "",
})

// Field-level WRITE ACL
snow_create_acl({
  name: "incident.priority",
  operation: "write",
  roles: ["incident_manager"],
  condition: "",
  script: "answer = current.state < 6;", // Only if not resolved
})

Common ACL Patterns

Pattern 1: Role-Based Access

// Condition: (empty - role check only)
// Roles: itil, incident_manager
// Script: (empty)

// Users with itil OR incident_manager role can access

Pattern 2: Ownership-Based Access

// Condition:
current.caller_id == gs.getUserID() || current.assigned_to == gs.getUserID() || current.opened_by == gs.getUserID()

// User can access their own records

Pattern 3: Group-Based Access

// Script:
;(function () {
  var userGroups = gs.getUser().getMyGroups()
  answer = userGroups.indexOf(current.assignment_group.toString()) >= 0
})()

// User can access records assigned to their groups

Pattern 4: Manager Chain Access

// Script:
;(function () {
  var callerManager = current.caller_id.manager
  var currentUser = gs.getUserID()

  // Check if current user is in caller's management chain
  while (callerManager && !callerManager.nil()) {
    if (callerManager.toString() == currentUser) {
      answer = true
      return
    }
    callerManager = callerManager.manager
  }
  answer = false
})()

Pattern 5: Time-Based Access

// Script:
;(function () {
  var now = new GlideDateTime()
  var hour = parseInt(now.getLocalTime().getHourOfDayLocalTime())

  // Only allow access during business hours (8 AM - 6 PM)
  answer = hour >= 8 && hour < 18
})()

Pattern 6: Data Classification

// Script:
;(function () {
  var classification = current.u_data_classification.toString()
  var userClearance = gs.getUser().getRecord().getValue("u_security_clearance")

  var levels = { public: 0, internal: 1, confidential: 2, secret: 3 }
  answer = levels[userClearance] >= levels[classification]
})()

Field-Level Security Patterns

Hide Sensitive Fields

// ACL: incident.u_ssn (Social Security Number)
// Operation: read
// Script:
answer = gs.hasRole("hr_admin")

// Only HR admins can see SSN field

Read-Only After State Change

// ACL: incident.short_description
// Operation: write
// Script:
answer = current.state < 6 // Can't edit after Resolved

// Prevent editing after resolution

Conditional Field Visibility

// ACL: incident.u_internal_notes
// Operation: read
// Condition:
gs.hasRole("itil") || current.caller_id == gs.getUserID()

// ITIL users see all, callers see their own

Security Best Practices

1. Principle of Least Privilege

// ❌ BAD - Too permissive
// Roles: (empty) - allows everyone

// ✅ GOOD - Explicit roles
// Roles: itil, incident_manager

2. Deny by Default

// Create a catch-all deny ACL at lowest priority
// Name: *
// Operation: read
// Condition: false
// This ensures anything not explicitly allowed is denied

3. Avoid Complex Scripts

// ❌ BAD - Complex script ACL (slow)
;(function () {
  var gr = new GlideRecord("sys_user_grmember")
  gr.addQuery("user", gs.getUserID())
  gr.query()
  while (gr.next()) {
    // Complex logic...
  }
})()

// ✅ GOOD - Use conditions when possible
// Condition: gs.getUser().isMemberOf(current.assignment_group)

4. Test ACLs Thoroughly

// Use "Impersonate User" to test ACLs as different users
// Check: Navigation, List views, Forms, Related lists
// Verify: Fields hidden, buttons disabled, records filtered

Debug ACLs

Enable ACL Debugging

// In a background script or temporarily in your code:
gs.setProperty("glide.security.debug", "true")
gs.log("ACL Debug enabled")

// Check System Logs for ACL evaluation details

Check User Permissions

// Check if current user can read a record
var gr = new GlideRecord("incident")
gr.get("sys_id_here")

gs.info("Can Read: " + gr.canRead())
gs.info("Can Write: " + gr.canWrite())
gs.info("Can Delete: " + gr.canDelete())

// Check field-level
gs.info("Can read assignment_group: " + gr.assignment_group.canRead())
gs.info("Can write assignment_group: " + gr.assignment_group.canWrite())

Common Mistakes

Mistake	Problem	Solution
No ACLs on custom tables	Anyone can access	Create ACLs immediately
Only role-based ACLs	No row-level security	Add conditions for data segregation
Scripts that query DB	Performance issues	Use conditions or cache results
Testing only as admin	Admin bypasses ACLs	Test as actual end users
Forgetting REST APIs	APIs bypass UI ACLs	Create specific REST ACLs