Microsoft 365 (M365) is now the backbone of the modern workplace. Users of Microsoft 365 services such as Exchange Online, SharePoint, Teams and Entra ID (Azure AD) use them every day for communication, collaboration and identity management. However, many administrators underestimate the risks arising from default configurations, and this is precisely where Microsoft 365 tenant hardening comes in.
Why is M365 tenant hardening important?
Many Microsoft 365 tenants run with the default settings, which are designed for functionality and user-friendliness rather than maximum security. This makes them a popular target for cyberattacks. Targeted hardening protects identities, data and communications, ideally before attackers can compromise them.
The default configuration is not secure
Factory settings prioritise convenience over security. Without customisation, potential entry points remain open.
A target for attackers
M365 is one of the most frequently attacked cloud systems worldwide. Phishing, account hijacking and token theft are commonplace.
Compliance and data protection
Requirements under ISO 27001, NIS2, the GDPR or the BSI’s IT-Grundschutz call for security measures that go beyond the standard.
Protection of business-critical data
Hardening prevents unauthorised access to identities, emails, documents and Teams communications.
Which components should be hardened?
Effective M365 hardening affects various areas of the tenant. Each of these levels poses specific risks that must be addressed individually.
- Entra ID (Azure AD): Mandatory multi-factor authentication, conditional access policies (e.g. IP- or device-based), controlled guest access, Privileged Identity Management (PIM) for administrator roles, active monitoring of login logs, deactivation of unused app registrations and legacy authentication, and assessment of high-risk logins and token issuance.
- Exchange Online: Correct configuration of SPF, DKIM and DMARC, regular assessment of anti-spam, anti-Malware and anti-Phishing policies, mail flow rules for DLP and encryption, disabling of insecure protocols such as POP3 and IMAP, and assessment of forwarding rules to prevent data leakage.
- SharePoint Online and OneDrive: Restrictive configuration of file sharing, classification of data using sensitivity labels, enabled audit logs to track file activity, and regular assessment and clean-up of external file shares.
- Microsoft Teams: Clear regulation or deactivation of guest access; control of external communication via directives; authorisation of verified apps only; and enabled auditing of meetings and chats.
- Microsoft Defender Suite: Activation of Defender for Office 365 to protect against malicious attachments and links; integration of Defender for Endpoint and Cloud Apps; configured security alerts with established Incident Response processes; and continuous threat hunting.
- Compliance and Governance: Enabled audit logs and Unified Audit; use of Data Loss Prevention (DLP) and eDiscovery; regular review of the Microsoft Secure Score; analysis of tenant configuration against security benchmarks; and monitoring of role changes and permission drift.
The added value of an M365 hardening
Enhanced security
Significantly reduces the attack surface and prevents unauthorised access.
Compliance and security
Meets regulatory requirements and facilitates audits.
Transparency & Control
Clear insights into user activities, permissions and risks.
Building trust
Customers, partners and auditors benefit from verifiable security.
Cost-effectiveness
Prevention saves costs by reducing security incidents.
Continuous improvement
Regular assessments and baseline checks ensure the tenant remains secure in the long term.
The process of a hardening project
Analysis
Review of the current configuration and security baseline.
Assessment
Prioritisation of risks and vulnerabilities.
implementation
Implementation of security measures in accordance with best practice.
Documentation and training
Handover of results and awareness raising amongst administrators.
Monitoring and review
Regular adjustments and progress monitoring based on up-to-date threat analyses.
Mint Secure GmbH
How Mint Secure supports you
We support organisations from the initial analysis right through to the ongoing Monitoring of their Microsoft 365 environment.
M365 Security Audit
We assess Entra ID, Exchange, SharePoint, Teams and the Defender configuration against recognised security benchmarks.
penetration test
We carry out targeted testing of your Cloud identities and configuration against real-world attack vectors.
consulting
We provide support with the implementation, documentation and ongoing Monitoring of your tenant hardening.
Conclusion
Microsoft 365 tenant hardening is not a one-off project, but an ongoing process. New features, threats and compliance requirements necessitate regular reviews.
Investing in security optimisation at an early stage strengthens your organisation’s long-term stability and resilience, and turns your M365 tenant into a trustworthy, robust platform for the entire organisation.
Mint Secure helps you secure your Microsoft 365 environment for the long term. Talk to us.
