Why CIS Benchmarks Matter for Microsoft 365
The Center for Internet Security (CIS) Benchmarks have become the de facto standard for secure configuration. When auditors ask "What security framework do you follow?", CIS is an answer they understand and respect.
For Microsoft 365 specifically, the CIS Microsoft 365 Foundations Benchmark provides prescriptive guidance across:
- Microsoft Entra ID (identity and access controls)
- Exchange Online (email security settings)
- SharePoint and OneDrive (data sharing controls)
- Microsoft Teams (collaboration security)
- Microsoft Defender (threat protection settings)
But here's the challenge: the benchmark contains over 150 individual recommendations. Implementing them all takes months. And not all recommendations carry equal weight for your organization.
This guide shows you how to approach CIS compliance practically—prioritizing high-impact controls, avoiding common pitfalls, and maintaining compliance over time.
Understanding CIS Benchmark Levels
The CIS Microsoft 365 Benchmark organizes recommendations into two levels:
Level 1 (L1): Essential Security
Level 1 recommendations are considered baseline security that every organization should implement. They:
- Have minimal impact on functionality or user experience
- Represent broad protection against common threats
- Are practical to implement without specialized expertise
Examples include requiring MFA for all users, blocking legacy authentication, and enabling audit logging.
Level 2 (L2): Defense in Depth
Level 2 recommendations provide additional protection for organizations with higher security requirements. They:
- May impact functionality or require user workflow changes
- Provide protection against more sophisticated threats
- Often require careful planning before implementation
Examples include session timeout policies, advanced threat protection settings, and granular sharing restrictions.
Practical advice: Start with L1 controls. They deliver the most security value with the least disruption. Only pursue L2 controls after L1 is fully implemented and stable.
The Top 15 CIS Controls to Implement First
Not all CIS recommendations are created equal. Based on threat data and real-world incidents, these controls should be your priority:
Identity and Access (Microsoft Entra ID)
1. Enable MFA for All Users (1.1.1)
The single most impactful security control. Microsoft reports that MFA blocks 99.9% of account compromise attacks.
Implementation tip: Use Conditional Access policies rather than per-user MFA for better management and flexibility.
2. Block Legacy Authentication (1.1.3)
Legacy protocols (POP, IMAP, SMTP AUTH) don't support MFA and are the primary vector for password spray attacks.
Implementation tip: Create the Conditional Access policy in report-only mode first. Review the sign-in logs for 2-4 weeks to identify any legitimate legacy auth usage before enforcing.
3. Limit Global Administrators (1.1.4)
CIS recommends no more than 4 Global Admins. Fewer privileged accounts means a smaller attack surface.
Implementation tip: Use Privileged Identity Management (PIM) to make admin access just-in-time rather than standing.
4. Enable Security Defaults or Equivalent (1.1.6)
If you're not using Conditional Access, Security Defaults provides baseline MFA and legacy auth blocking.
Implementation tip: Organizations using Conditional Access should disable Security Defaults and implement equivalent controls through CA policies for more granular control.
5. Configure Password Policies (1.1.7-1.1.9)
Disable password expiration (per NIST guidance), enable banned password lists, and configure smart lockout.
Implementation tip: Password expiration causes users to create weaker passwords. Modern guidance recommends no expiration combined with MFA and breach detection.
Exchange Online
6. Enable Audit Logging (2.1.1)
Unified audit logging must be enabled to have visibility into user and admin activities.
Implementation tip: Verify logging is enabled—it should be by default for new tenants, but older tenants may need manual enablement.
7. Configure Anti-Phishing Policies (2.1.4)
Enable impersonation protection, mailbox intelligence, and safety tips.
Implementation tip: Start with standard protection, then tune based on false positives before moving to strict.
8. Enable Safe Attachments (2.1.6)
Detonate attachments in a sandbox before delivery to catch zero-day malware.
Implementation tip: Use Dynamic Delivery to avoid delays—users get the email immediately while attachments are scanned.
9. Enable Safe Links (2.1.7)
URL rewriting and time-of-click verification protects against delayed phishing attacks.
Implementation tip: Enable for all Microsoft 365 apps, not just email.
SharePoint and OneDrive
10. Limit External Sharing (3.1.1)
Configure sharing to require authentication at minimum. Consider restricting to specific domains.
Implementation tip: Work with business stakeholders before restricting. External sharing is often critical for business processes.
11. Block Sync from Unmanaged Devices (3.2.1)
Prevent data from syncing to personal computers outside IT control.
Implementation tip: This requires Intune device compliance or hybrid Azure AD join to identify managed devices.
Microsoft Teams
12. Restrict External Access (4.1)
Control which external domains can communicate with your users via Teams.
Implementation tip: "Allow all" is the default and highest risk. Consider "Allow specific domains" for known partners.
13. Disable Anonymous Meeting Join (4.3)
Require authentication for meeting participants when possible.
Implementation tip: Balance security with usability. Some organizations need anonymous join for customer-facing meetings.
Defender for Office 365
14. Enable Safe Documents (5.2.1)
Scans Office documents opened in Protected View before allowing editing.
Implementation tip: Requires Microsoft 365 E5 or Defender for Office 365 Plan 2.
15. Configure Alert Policies (5.3.1)
Enable built-in alert policies for suspicious activities like impossible travel or malware detection.
Implementation tip: Review default alert policies and tune thresholds based on your environment.
Common CIS Implementation Mistakes
Mistake 1: Implementing Controls Without Testing
The biggest CIS project killer: enabling a control that breaks a critical business process.
The fix: Always use report-only mode or staged rollouts. For every control:
- Enable in report-only/audit mode
- Monitor for 2-4 weeks
- Address any issues found
- Then enforce
Mistake 2: Treating It as a One-Time Project
CIS compliance isn't "done" when you implement the controls. Configurations drift over time:
- New admins may not know about CIS requirements
- Support tickets lead to "temporary" exceptions that become permanent
- Microsoft updates change default behaviors
- New features introduce new settings that need configuration
The fix: Implement continuous monitoring. Check your configuration against CIS baselines weekly, not annually.
Mistake 3: Ignoring Business Context
CIS provides recommendations. Your organization provides context. Not every recommendation fits every business.
Example: CIS recommends blocking all external sharing in SharePoint. But if your business depends on sharing files with clients, blanket blocking destroys workflows.
The fix: Document exceptions with business justification. "We allow external sharing to these 5 partner domains because [business reason]" is a valid position for auditors.
Mistake 4: No Emergency Access Plan
Implementing strong access controls without break-glass accounts creates lockout risk.
The fix: Before enforcing access controls, create 2+ emergency access accounts that:
- Are excluded from Conditional Access policies
- Use hardware FIDO2 keys (not phone-based MFA)
- Have credentials stored securely offline
- Are monitored for any usage
Mistake 5: Skipping Documentation
"We implemented CIS" isn't enough. Auditors want evidence:
- Which controls did you implement?
- When were they implemented?
- What exceptions exist and why?
- How do you verify ongoing compliance?
The fix: Maintain a CIS compliance matrix documenting each control's status, implementation date, and any exceptions.
Building a CIS Implementation Timeline
Phase 1: Foundation (Weeks 1-4)
Week 1-2: Assessment
- Export current tenant configuration
- Map existing controls to CIS recommendations
- Identify gaps
Week 3-4: Quick Wins
- Enable audit logging
- Configure password policies
- Create emergency access accounts
- Enable Security Defaults (if not using CA)
Phase 2: Identity Controls (Weeks 5-12)
Week 5-6: MFA Foundation
- Create MFA Conditional Access policy (report-only)
- Monitor sign-in logs for issues
- Communicate to users
Week 7-8: MFA Enforcement
- Enforce MFA policy
- Address any user issues
- Document exceptions
Week 9-10: Legacy Auth Blocking
- Create legacy auth block policy (report-only)
- Identify legitimate legacy auth usage
- Work with app owners on alternatives
Week 11-12: Privileged Access
- Audit Global Admin accounts
- Implement PIM for admin roles
- Configure admin MFA requirements
Phase 3: Email Security (Weeks 13-20)
Week 13-14: Anti-Phishing
- Configure impersonation protection
- Enable mailbox intelligence
- Set up user-reported phishing process
Week 15-16: Safe Attachments & Links
- Enable Safe Attachments (Dynamic Delivery)
- Enable Safe Links for all apps
- Monitor for false positives
Week 17-20: Advanced Email Protection
- Configure DMARC, DKIM, SPF
- Set up mail flow rules per CIS guidance
- Enable alert policies
Phase 4: Data Protection (Weeks 21-28)
Week 21-24: SharePoint/OneDrive
- Review external sharing settings
- Configure guest access policies
- Implement device access restrictions
Week 25-28: Teams
- Configure external access settings
- Review meeting policies
- Set up guest access controls
Phase 5: Ongoing Compliance
- Weekly: Automated configuration scans
- Monthly: Review exceptions and alerts
- Quarterly: Full CIS assessment
- Annually: Complete benchmark review against latest CIS version
Automating CIS Compliance Monitoring
Manual CIS compliance is unsustainable. You need automation.
What to Monitor Automatically
Configuration drift: Did someone re-enable legacy auth? Did a new admin get permanent Global Admin instead of PIM eligible?
New resources: When new users, groups, or applications are created, do they meet CIS requirements?
Policy changes: When Conditional Access policies change, do they still meet CIS baselines?
Building vs. Buying
You can build CIS monitoring with:
- PowerShell scripts querying Microsoft Graph
- Azure Logic Apps for alerting
- Power BI for dashboards
This works but requires significant development and maintenance effort.
Alternatively, platforms like TrueConfig provide:
- Pre-built CIS control mappings
- Continuous configuration monitoring
- Automatic drift detection and alerting
- One-click remediation for common deviations
The build-vs-buy decision depends on your team's capacity and the value of their time.
Mapping CIS to Other Frameworks
CIS doesn't exist in isolation. Here's how it maps to other common frameworks:
| CIS Control Area | SOC 2 Trust Criteria | ISO 27001 | NIST CSF |
|---|---|---|---|
| MFA/Access Control | CC6.1, CC6.2 | A.9.4 | PR.AC |
| Audit Logging | CC7.2 | A.12.4 | DE.CM |
| Data Protection | CC6.7 | A.13.2 | PR.DS |
| Incident Response | CC7.3, CC7.4 | A.16.1 | RS.RP |
If you're implementing CIS for Microsoft 365, you're simultaneously making progress on SOC 2, ISO 27001, and other frameworks.
Handling CIS Audits
When auditors assess your CIS compliance, they want to see:
1. Evidence of Implementation
- Screenshots of current configuration
- Policy documents showing settings
- Configuration export files
2. Ongoing Monitoring
- Reports showing regular compliance checks
- Drift detection and remediation records
- Alert history showing issues were addressed
3. Exception Management
- Documented business justifications for any deviations
- Approval records for exceptions
- Compensating controls where full implementation isn't possible
4. Change Management
- Evidence that configuration changes go through review
- Audit trail of who changed what and when
- Rollback procedures for problematic changes
Getting Started Today
CIS compliance for Microsoft 365 is achievable. Start with these steps:
-
Download the benchmark: Get the latest CIS Microsoft 365 Foundations Benchmark from cisecurity.org
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Run a gap assessment: Use Microsoft's built-in tools or third-party solutions to assess current state
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Prioritize L1 controls: Focus on the 15 high-impact controls listed above
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Create emergency access: Before enforcing access controls, ensure you have break-glass accounts
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Implement in phases: Follow the timeline above, always testing before enforcing
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Automate monitoring: Manual compliance checks don't scale—implement continuous monitoring
The organizations that succeed with CIS don't try to implement everything at once. They prioritize ruthlessly, test thoroughly, and monitor continuously.
TrueConfig maps Microsoft 365 security controls to CIS benchmarks, continuously monitoring your tenant for compliance drift. When configurations deviate from your CIS baseline, you know immediately—and can remediate with one click. Start your free assessment