Microsoft 365 Security Baseline 2026
Microsoft 365 is a critical business platform and a frequent target for cyberattacks. This security baseline provides essential controls to protect Entra ID, Exchange Online, Teams, OneDrive, and SharePoint.
1. Enable Multi-Factor Authentication (MFA)
MFA should be mandatory for all users, especially administrators.
- Enable MFA for all accounts.
- Require MFA for Global Administrators.
- Use Microsoft Authenticator.
- Disable legacy authentication.
2. Implement Conditional Access
Conditional Access helps protect against unauthorized access attempts.
- Block sign-ins from risky locations.
- Require MFA for external access.
- Restrict access from unmanaged devices.
- Protect privileged accounts.
3. Secure Administrator Accounts
- Use separate admin accounts.
- Enable Privileged Identity Management (PIM).
- Review admin roles regularly.
- Remove unused admin accounts.
4. Secure Exchange Online
- Enable Anti-Phishing Policies.
- Enable Safe Links.
- Enable Safe Attachments.
- Configure SPF, DKIM and DMARC.
- Monitor mail forwarding rules.
5. Protect SharePoint and OneDrive
- Restrict external sharing.
- Enable file versioning.
- Monitor anonymous links.
- Review sharing permissions regularly.
6. Secure Microsoft Teams
- Restrict guest access.
- Review third-party app permissions.
- Enable compliance auditing.
- Monitor external users.
7. Enable Microsoft Defender
- Microsoft Defender for Office 365.
- Microsoft Defender for Endpoint.
- Microsoft Defender for Identity.
- Microsoft Defender for Cloud Apps.
8. Enable Audit Logging
Unified Audit Logging should always be enabled.
- Track user activities.
- Monitor mailbox actions.
- Review sign-in logs.
- Investigate suspicious events.
9. Backup Microsoft 365 Data
Microsoft recommends customers maintain independent backups.
- Backup Exchange Online.
- Backup SharePoint.
- Backup OneDrive.
- Backup Teams data.
10. Monitor Security Score
Use Microsoft Secure Score to continuously improve your security posture.
- Review recommendations monthly.
- Track security improvements.
- Prioritize high-risk findings.
Recommended Security Stack
- Microsoft Entra ID Premium P1/P2
- Conditional Access
- Microsoft Defender for Office 365
- Microsoft Defender for Endpoint
- Microsoft Sentinel SIEM
- Third-party Backup Solution
Conclusion
A properly secured Microsoft 365 environment significantly reduces the risk of phishing, ransomware, account compromise, and data leakage. Organizations should continuously review security settings and follow Microsoft's recommended security baselines.
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