# Audit logs SHALL be maintained for at least the minimum duration dictated by OMB M-21-31 (Appendix C)

Audit logs SHALL be maintained for at least the minimum duration dictated by OMB M-21-31 (Appendix C).

Source: https://maester.dev/docs/tests/CISA.MS.EXO.17.3

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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><a class="test-byline-avatar" href="/contributors/thomas-s-schmidt" title="Thomas Schmidt · Co-contributor"><img src="https://github.com/thomas-s-schmidt.png" alt="Thomas Schmidt" 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> with <a href="/contributors/thomas-s-schmidt">Thomas Schmidt</a></span><a class="test-byline-link" href="/contributors">All contributors →</a></div></div>

<p class="test-part">Part of <a href="/docs/tests/cisa">CISA</a> · Exchange Online · Audit logging · <a href="/docs/tests">All checks</a></p>

```powershell title="Run this check"
Invoke-Maester -TestId CISA.MS.EXO.17.3
```

## Overview

Audit logs SHALL be maintained for at least the minimum duration dictated by OMB M-21-31 (Appendix C).

Rationale: Audit logs may no longer be available when needed if they are not retained for a sufficient time. Increased log retention time gives an agency the necessary visibility to investigate incidents that occurred some time ago. OMB M-21-13, Appendix C, Table 5 specifically calls out Unified Audit Logs in the Cloud Azure log category.

#### Remediation action

To create one or more custom audit retention policies, if the default retention policy is not sufficient for agency needs, follow [Create an audit log retention policy](https://learn.microsoft.com/purview/audit-log-retention-policies?view=o365-worldwide&tabs=microsoft-purview-portal#create-an-audit-log-retention-policy) instructions. Ensure the duration selected in the retention policies is at least one year, in accordance with OMB M-21-31.

#### Related links

* [Purview portal - Audit policies](https://purview.microsoft.com/audit/auditpolicies)
* [CISA 17 Audit Logging - MS.EXO.17.3](https://github.com/cisagov/ScubaGear/blob/main/PowerShell/ScubaGear/baselines/exo.md#msexo173v1)
* [CISA ScubaGear Rego Reference](https://github.com/cisagov/ScubaGear/blob/main/PowerShell/ScubaGear/Rego/EXOConfig.rego#L928)

## Details

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

| Field | Value |
| --- | --- |
| Test ID | CISA.MS.EXO.17.3 |
| Severity | Medium |
| Suite | CISA |
| Product | Exchange Online |
| Related products | Purview |
| Feature | Audit logging |
| Area | Logging and detection |
| Resource type | Tenant |
| User impact | Low |
| Implementation cost | Low |
| MITRE ATT&CK | T1070 Indicator Removal |
| Supports benchmark | CISA SCuBA Secure Configuration Baselines for Microsoft 365 (version ScubaGear main, 2026-10-11), requirement MS.EXO.17.3 |
| Criticality | SHALL |
| Upstream requirement | Moved to MS.SECURITYSUITE.5.2v1 (was MS.EXO.17.3v1) |
| Supports controls | cisa-scuba:MS.EXO.17.3, nist-800-53-r5:AU-11 |
| PowerShell test | [Test-MtCisaAuditLogRetention](https://github.com/maester365/maester/blob/main/tests/cisa/exchange/Test.CISA.MS.EXO.17.3.ps1) |
| Services | ExchangeOnline, Graph, SecurityCompliance |
| Compatible licenses | M365_ADVANCED_AUDITING |

</details>

## Source

- Test: [`tests/cisa/exchange/Test.CISA.MS.EXO.17.3.ps1`](https://github.com/maester365/maester/blob/main/tests/cisa/exchange/Test.CISA.MS.EXO.17.3.ps1)
- Documentation: [`tests/cisa/exchange/Test.CISA.MS.EXO.17.3.md`](https://github.com/maester365/maester/blob/main/tests/cisa/exchange/Test.CISA.MS.EXO.17.3.md)