# SPN mappings should be retrievable

SPN mappings are used to support legacy or non-FQDN client behavior by mapping service principal names to the correct Kerberos realm/host context.

Source: https://maester.dev/docs/tests/AD-CFG-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 · Directory configuration · <a href="/docs/tests">All checks</a></p>

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

## Overview

**SPN mappings** are used to support legacy or non-FQDN client behavior by mapping service principal names to the correct Kerberos realm/host context. While this can improve compatibility, misconfigured SPN mappings can create security and reliability issues, such as:

- **Authentication inconsistencies** (Kerberos vs. fallback behaviors)
- Clients receiving **unexpected service identity** resolution
- Increased exposure to **credential forwarding / downgrade-style** scenarios if legacy behavior is unintentionally permitted

#### Control Type

**Operational**

#### Security Recommendation
- Keep SPN mappings **as minimal as possible**—only those required for supported legacy interoperability.
- Periodically review and remove stale mappings tied to retired hostnames/services.
- Validate that SPN mappings resolve to the **correct** target identities (FQDN/realm) for all required workloads.

#### How the Test Works
This test inspects the SPN mapping configuration exposed by AD, extracts the configured mappings, and provides a count/visibility metric so administrators can identify whether mappings exist that should not be present.

#### Related Tests
- `Test-MtAdWellKnownSecurityPrincipalsCount` - Identifies additional security principal surface that should be consistent with Kerberos hardening.

## Details

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

| Field | Value |
| --- | --- |
| Test ID | AD-CFG-03 |
| Severity | Info |
| Suite | Active Directory |
| Product | Active Directory |
| Feature | Directory configuration |
| Area | Infrastructure hardening |
| Resource type | Tenant |
| MITRE ATT&CK | None |
| PowerShell test | [Test-MtAdSpnMappings](https://github.com/maester365/maester/blob/main/tests/ad/config/Test.AD-CFG-03.ps1) |
| Services | ActiveDirectory |
| Permissions | ActiveDirectory:Ldap:Configuration/*:ReadProperty |

</details>

## Source

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