# Calendar details SHALL NOT be shared with all domains

Calendar details SHALL NOT be shared with all domains. A Maester check for Exchange Online, Calendar and contact sharing.

Source: https://maester.dev/docs/tests/CISA.MS.EXO.6.2

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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/nzlostboy" title="Ben Miles · Co-contributor"><img src="https://github.com/NZLostboy.png" alt="Ben Miles" width="28" height="28" loading="lazy" decoding="async" /></a><a class="test-byline-avatar" href="/contributors/merill" title="Merill Fernando · Co-contributor"><img src="https://github.com/merill.png" alt="Merill Fernando" 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 2 co-contributors</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 · Calendar and contact sharing · <a href="/docs/tests">All checks</a></p>

```powershell title="Run this check"
Invoke-Maester -TestId CISA.MS.EXO.6.2
```

## Overview

Calendar details SHALL NOT be shared with all domains.

Rationale: Calendar details may contain information that should not be shared by default with all domains. Disabling sharing with all domains closes an avenue for data exfiltration while still allowing for legitimate use as needed.

#### Remediation action:

To restrict sharing with all domains:
1. Sign in to the **Exchange admin center**.
2. On the left-hand pane under **Organization**, select **Sharing**.
3. Select [**Individual Sharing**](https://admin.exchange.microsoft.com/#/individualsharing).
4. For all existing policies, select the policy, then select **Manage domains**.
5. For all sharing rules under all existing policies, ensure **Sharing with everyone** and **Anonymous** do not include CalendarSharing.

#### Related links

* [Exchange admin center - Individual Sharing](https://admin.exchange.microsoft.com/#/individualsharing)
* [Microsoft 365 admin center - Org settings - Calendar](https://admin.microsoft.com/#/Settings/Services/:/Settings/L1/Calendar)
* [CISA 6 Calendar and Contact Sharing - MS.EXO.6.2v1](https://github.com/cisagov/ScubaGear/blob/main/PowerShell/ScubaGear/baselines/exo.md#msexo62v1)
* [CISA ScubaGear Rego Reference](https://github.com/cisagov/ScubaGear/blob/main/PowerShell/ScubaGear/Rego/EXOConfig.rego#L368)

## Details

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

| Field | Value |
| --- | --- |
| Test ID | CISA.MS.EXO.6.2 |
| Severity | Medium |
| Suite | CISA |
| Product | Exchange Online |
| Feature | Calendar and contact sharing |
| Area | External access and sharing |
| Resource type | Policy |
| User impact | Low |
| Implementation cost | Low |
| MITRE ATT&CK | T1048 Exfiltration Over Alternative Protocol, T1567 Exfiltration Over Web Service, T1591 Gather Victim Org Information |
| Supports benchmark | CISA SCuBA Secure Configuration Baselines for Microsoft 365 (version ScubaGear main, 2026-10-11), requirement MS.EXO.6.2 |
| Criticality | SHALL |
| Upstream requirement | MS.EXO.6.2v1 |
| Supports controls | cisa-scuba:MS.EXO.6.2, nist-800-53-r5:AC-3, nist-800-53-r5:SC-7(10)(a) |
| PowerShell test | [Test-MtCisaCalendarSharing](https://github.com/maester365/maester/blob/main/tests/cisa/exchange/Test.CISA.MS.EXO.6.2.ps1) |
| Services | ExchangeOnline |

</details>

## Source

- Test: [`tests/cisa/exchange/Test.CISA.MS.EXO.6.2.ps1`](https://github.com/maester365/maester/blob/main/tests/cisa/exchange/Test.CISA.MS.EXO.6.2.ps1)
- Documentation: [`tests/cisa/exchange/Test.CISA.MS.EXO.6.2.md`](https://github.com/maester365/maester/blob/main/tests/cisa/exchange/Test.CISA.MS.EXO.6.2.md)