# Computer SPN service class count should be retrievable

Service Principal Names (SPNs) are critical for Kerberos authentication in Active Directory.

Source: https://maester.dev/docs/tests/AD-SPN-01

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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 · Service principal names · <a href="/docs/tests">All checks</a></p>

```powershell title="Run this check"
Invoke-Maester -TestId AD-SPN-01
```

## Overview

Service Principal Names (SPNs) are critical for Kerberos authentication in Active Directory. Understanding the distribution of SPN service classes helps security teams:

- **Identify service exposure**: Know what services are exposed for Kerberos authentication
- **Detect anomalies**: Unusual SPN service classes may indicate unauthorized services or misconfigurations
- **Audit service footprint**: Track the services running across your infrastructure
- **Kerberoasting assessment**: SPNs are required for Kerberoasting attacks; knowing what exists helps assess risk

Common SPN service classes include HOST, HTTP, LDAP, MSSQLSvc, and CIFS. Unexpected service classes may warrant investigation.

#### Control Type

**Operational**

#### Security Recommendation

Regularly audit SPN configurations to ensure:
- Only authorized services have SPNs registered
- SPNs are registered on the correct accounts
- Unused or legacy service SPNs are removed
- Sensitive SPNs (like those for database services) are properly secured

#### How the Test Works

This test retrieves all computer objects from Active Directory, extracts their SPNs, and counts the distinct service classes. An SPN has the format `serviceclass/host:port`, and this test focuses on the service class portion.

#### Related Tests

- `Test-MtAdComputerSpnServiceClassUsage` - Shows usage breakdown of each service class
- `Test-MtAdComputerSpnUnknownCount` - Identifies unrecognized SPN service classes
- `Test-MtAdUserSpnServiceClassCount` - Counts distinct service classes on user accounts

## Details

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

| Field | Value |
| --- | --- |
| Test ID | AD-SPN-01 |
| Severity | Info |
| Suite | Active Directory |
| Product | Active Directory |
| Feature | Service principal names |
| Area | Infrastructure hardening |
| Resource type | Computer |
| MITRE ATT&CK | None |
| PowerShell test | [Test-MtAdComputerSpnServiceClassCount](https://github.com/maester365/maester/blob/main/tests/ad/spn/Test.AD-SPN-01.ps1) |
| Services | ActiveDirectory |
| Permissions | ActiveDirectory:Ldap:computer:ReadProperty |

</details>

## Source

- Test: [`tests/ad/spn/Test.AD-SPN-01.ps1`](https://github.com/maester365/maester/blob/main/tests/ad/spn/Test.AD-SPN-01.ps1)
- Documentation: [`tests/ad/spn/Test.AD-SPN-01.md`](https://github.com/maester365/maester/blob/main/tests/ad/spn/Test.AD-SPN-01.md)