Why Is Microsoft 365 a Target for Attacks?
Microsoft 365 is the most widely adopted SaaS platform in corporate environments, with over 300 million commercial users worldwide. This prevalence also makes it an attractive target for attackers. The majority of cybersecurity incidents involving M365 environments reveal the following issues:
- Weak or reused passwords
- Accounts without MFA enabled
- Overly broad administrator permissions
- Email configurations vulnerable to phishing
- Unmonitored sign-in activity
A default M365 deployment provides only a minimum level of security. Additional configuration is required to achieve enterprise-grade security.
Core Security Steps
1. Apply MFA to All Accounts
According to Microsoft data, MFA blocks account takeover attacks at a rate of 99.9%. MFA must be enforced for all users — and especially for administrator accounts — through Conditional Access policies.
Recommendation for Global Administrator accounts: Microsoft Authenticator with push notification and number matching must be active.
2. Conditional Access Policies
Azure AD Conditional Access provides condition-based answers to the questions "Who, from where, with what device, and to which application is access being requested?":
- Sign-in from unknown geographies → MFA or block
- Sign-in from an unmanaged device → restricted access
- Risky sign-in detected → additional verification
- Privileged roles → MFA always required
3. Security Defaults or Custom Policies
If Security Defaults are not enabled on your M365 tenant, minimum security measures are not active. While Security Defaults serve as a quick starting point for smaller organizations, custom Conditional Access policies provide greater flexibility for enterprise requirements.
Email Security
DKIM, DMARC, and SPF
These three DNS records, which prevent email spoofing, must be configured in all Microsoft 365 environments:
- SPF: Defines which servers are permitted to send email on behalf of your domain
- DKIM: Verifies via cryptographic signature that email content has not been altered
- DMARC: Determines what happens to an email when SPF and DKIM fail (quarantine / reject)
Without a DMARC policy set to p=reject, your domain can be impersonated in phishing attacks.
Microsoft Defender for Office 365
An advanced threat protection layer built on top of Exchange Online Protection:
- Safe Links: Analyzes links in emails and Office documents at the moment of click
- Safe Attachments: Opens attachments in a virtual environment to check for malicious content
- Anti-Phishing: Impersonation protection and phishing detection
- Attack Simulator: Measures user awareness through controlled phishing simulations
Identity Management and Access Control
Privileged Identity Management (PIM)
Microsoft Entra Privileged Identity Management prevents administrator roles from being permanently assigned. Administrators activate a role only for the duration they need it, through an approval mechanism. This approach prevents a compromised administrator account from causing permanent damage.
Service Accounts and Application Permissions
OAuth permissions granted to third-party applications should be reviewed regularly, and permissions for unused applications should be revoked. Microsoft 365 App Governance forms the center of this console.
Monitoring Sign-In Logs
Azure AD Sign-in Logs and Audit Logs should be forwarded to Microsoft Sentinel or a third-party SIEM to detect anomalous activity:
- Sign-ins from unusual geographies
- Sign-ins from different countries within a short period (impossible travel)
- Bulk file downloads or the creation of email forwarding rules
Data Protection
Microsoft Purview DLP
Detects sensitive data (national ID numbers, IBANs, credit cards, health data) in Exchange Online, SharePoint, OneDrive, and Teams, and restricts its sharing. Reduces the risk of personal data leakage under KVKK.
Sensitivity Labels
Confidential documents can be labeled; encryption, print restrictions, and external sharing blocks are automatically applied based on the label level.
Self-Service Password Reset (SSPR) and Tenant Restrictions
By enabling Self-Service Password Reset (SSPR), the helpdesk workload can be reduced; with Tenant Restrictions, users can be limited to accessing only approved M365 accounts from corporate devices.
Microsoft 365 Secure Score
The Secure Score in the Microsoft 365 Defender portal rates your security configuration on a scale of 0–100 and lists priority improvement actions. Applying the recommended actions in order is the most practical way to systematically strengthen your security posture.
Conclusion
Microsoft 365 security is achieved not merely by purchasing a license, but through correct configuration. MFA, Conditional Access, DMARC, and Defender configurations constitute the baseline security hygiene; advanced features such as PIM and DLP address enterprise compliance requirements. As NRC Sistem, we provide consulting services for Microsoft 365 security assessments, Secure Score improvement, Conditional Access policy design, and Microsoft Defender configuration.