# SPN suffixes count should be retrievable

SPN (Service Principal Name) suffixes simplify Service Principal Name management in complex Active Directory environments. They are important for:

Source: https://maester.dev/docs/tests/AD-FORS-03

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<div class="test-byline"><div class="test-byline-avatars"><a class="test-byline-avatar test-byline-avatar--author" href="/contributors/soulemike" title="Michael Soule · Original author"><img src="https://github.com/soulemike.png" alt="Michael Soule" width="28" height="28" loading="lazy" decoding="async" /></a></div><div class="test-byline-meta"><span class="test-byline-text">Contributed by <a href="/contributors/soulemike">Michael Soule</a></span><a class="test-byline-link" href="/contributors">All contributors →</a></div></div>

<p class="test-part">Part of <a href="/docs/tests/ad">Active Directory</a> · Active Directory · Domain and forest · <a href="/docs/tests">All checks</a></p>

```powershell title="Run this check"
Invoke-Maester -TestId AD-FORS-03
```

## Overview

SPN (Service Principal Name) suffixes simplify Service Principal Name management in complex Active Directory environments. They are important for:

- **Service Authentication**: SPNs are used by Kerberos to authenticate services; suffixes provide flexibility in how services are registered
- **Multi-Domain Services**: Organizations hosting services across multiple DNS namespaces use SPN suffixes to simplify SPN registration
- **Service Migration**: SPN suffixes enable service migration between domains without changing service configurations
- **Security Assessment**: Understanding SPN suffix configuration helps identify potential Kerberos authentication attack surfaces

#### Control Type

**Operational**

#### Security Recommendation

Review SPN suffix configuration regularly:
- Ensure only legitimate organizational DNS domains are configured as SPN suffixes
- Remove unused SPN suffixes that may have been added for completed projects
- Verify that SPN suffixes align with the organization's service hosting strategy
- Monitor for unauthorized SPN suffix additions which could indicate compromise

#### How the Test Works

This test retrieves the SPN suffixes configured at the forest level using the `Get-ADForest` cmdlet. It counts the number of custom SPN suffixes and reports the configuration status. The default forest domain is available for SPN registration by default and is not counted as a custom suffix.

#### Related Tests

- `Test-MtAdUpnSuffixesCount` - Checks UPN suffix configuration for user authentication
- `Test-MtAdUpnSuffixesDetails` - Provides detailed UPN suffix information

## Details

<details>
<summary>Every attribute of this check</summary>

| Field | Value |
| --- | --- |
| Test ID | AD-FORS-03 |
| Severity | Info |
| Suite | Active Directory |
| Product | Active Directory |
| Feature | Domain and forest |
| Area | Infrastructure hardening |
| Resource type | Tenant |
| MITRE ATT&CK | None |
| PowerShell test | [Test-MtAdSpnSuffixesCount](https://github.com/maester365/maester/blob/main/tests/ad/domain/Test.AD-FORS-03.ps1) |
| Services | ActiveDirectory |
| Permissions | ActiveDirectory:Ldap:crossRef:ReadProperty |

</details>

## Source

- Test: [`tests/ad/domain/Test.AD-FORS-03.ps1`](https://github.com/maester365/maester/blob/main/tests/ad/domain/Test.AD-FORS-03.ps1)
- Documentation: [`tests/ad/domain/Test.AD-FORS-03.md`](https://github.com/maester365/maester/blob/main/tests/ad/domain/Test.AD-FORS-03.md)