# User SPN unknown service class count should be investigated

Unknown SPN service classes on user accounts require immediate attention because:

Source: https://maester.dev/docs/tests/AD-SPN-09

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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-09
```

## Overview

Unknown SPN service classes on user accounts require immediate attention because:

- **High risk**: User accounts with SPNs are Kerberoasting targets
- **Shadow IT**: Unknown services may bypass security controls
- **Misconfigurations**: Could indicate improper SPN registration
- **Compliance issues**: Unauthorized services violate security policies

User accounts are preferred targets for Kerberoasting, making unknown SPNs on these accounts particularly concerning.

#### Control Type

**Operational**

#### Security Recommendation

Investigate all unknown SPNs on user accounts:
- Determine the service owner and business justification
- Verify if the service requires a user account or can use gMSA
- Check for misconfigurations or typos
- Remove unauthorized SPNs immediately
- Document approved custom SPNs

#### How the Test Works

This test compares discovered user SPN service classes against a database of known SPNs and flags any unrecognized service classes for investigation.

#### Related Tests

- `Test-MtAdUserSpnUnknownDetails` - Detailed information about unknown user SPNs
- `Test-MtAdComputerSpnUnknownCount` - Unknown SPNs on computer accounts
- `Test-MtAdUserSpnServiceClassCount` - All user SPN service classes

## Details

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

| Field | Value |
| --- | --- |
| Test ID | AD-SPN-09 |
| Severity | Info |
| Suite | Active Directory |
| Product | Active Directory |
| Feature | Service principal names |
| Area | Authentication |
| Resource type | User |
| MITRE ATT&CK | T1558.003 Kerberoasting |
| PowerShell test | [Test-MtAdUserSpnUnknownCount](https://github.com/maester365/maester/blob/main/tests/ad/spn/Test.AD-SPN-09.ps1) |
| Services | ActiveDirectory |
| Permissions | ActiveDirectory:Ldap:user:ReadProperty |

</details>

## Source

- Test: [`tests/ad/spn/Test.AD-SPN-09.ps1`](https://github.com/maester365/maester/blob/main/tests/ad/spn/Test.AD-SPN-09.ps1)
- Documentation: [`tests/ad/spn/Test.AD-SPN-09.md`](https://github.com/maester365/maester/blob/main/tests/ad/spn/Test.AD-SPN-09.md)