Microsoft 365 offers strong built-in security, but a missing or misconfigured security setting can leave your environment exposed. Here are five common Microsoft 365 security oversights that put organizations at risk and how to fix them. These apply across Microsoft 365 Enterprise, Business, and Education tenants.
The problem: In 2024, Microsoft announced that it would begin to roll out mandatory MFA for some applications, including Azure and the Microsoft 365 admin center. Still, ****Many Microsoft 365 tenants still don’t require multi-factor authentication (MFA) for every user. By default, MFA isn’t enforced unless Security Defaults or Conditional Access policies are in place. That means users may still be able to log in with just a password.
Why it’s risky: Passwords alone aren’t enough. They’re vulnerable to phishing, credential stuffing, and password spray attacks. Microsoft reports that over 99.9% of compromised accounts had MFA disabled. If attackers get credentials, they can walk right in—especially if legacy protocols are enabled (more on that below).
How to fix it:
Bottom line: Enforcing MFA is the single most effective step you can take to secure Microsoft 365. It turns stolen passwords into dead ends.
The problem: Legacy authentication protocols like POP3, IMAP, and SMTP don’t support modern MFA. While Microsoft is phasing them out, many tenants still have them enabled—sometimes by accident.
Why it’s risky: Legacy protocols are a popular target for password spray attacks because they bypass MFA entirely. Even if MFA is enabled, a single exposed protocol can be used as a backdoor. Microsoft telemetry shows that many compromised sign-ins originate from legacy auth clients.
How to fix it:
Bottom line: Disabling legacy authentication ensures that every sign-in goes through modern auth, where MFA and Conditional Access policies can do their job.
The problem: It’s common for organizations to assign too many users the Global Administrator (GA) role in Microsoft 365. Sometimes, IT teams share a GA account, or staff keep admin privileges long after they’re needed. Many also skip using dedicated admin accounts, performing privileged tasks from their everyday logins.
Why it’s risky: Global Admins can change security settings, access user data, create accounts, and more. Given the high level of privilege, every GA account is a top-tier target for attackers. If just one is compromised, your entire tenant is at risk. Over-provisioned access also means a greater chance of accidental misconfiguration. Worse yet, using a GA account for "daily driving" activities like checking email, signing into enterprise applications, or browsing the internet increases the odds of phishing or malware exposure.
How to fix it:
Bottom line: The fewer standing Global Admins you have, the fewer paths an attacker can exploit. Least privilege isn’t just a best practice—it’s a survival strategy.
The problem: By default, Microsoft 365 allows users to share files via anonymous links that don’t require sign-in. The default link type is often set to “Anyone with the link,” and Teams allows external guests by default, unless explicitly restricted. Without careful oversight, users can unintentionally expose sensitive content to the public.
Why it’s risky: Anonymous links can be forwarded to anyone, and there’s no audit trail of who accessed them. That makes it easy for sensitive data to leak outside the organization without detection. Over time, sprawling external shares and unmanaged guest access increase your risk surface. If OneDrive is allowed to sync to unmanaged devices, data can end up on personal machines with weak security—or remain there after an employee leaves.
How to fix it:
Bottom line: Collaboration doesn’t have to mean open season on your data. Set sharing defaults that protect sensitive files and review them regularly. If you don’t control external access, someone else will.
The problem: Email remains the most common entry point for phishing, malware, and business email compromise (BEC). While Microsoft 365 includes strong email security features, many organizations don’t fully configure them. Common oversights include failing to set up SPF, DKIM, and DMARC email authentication protocols and leaving anti-phishing and anti-spam policies at their default settings in Exchange Online Protection (EOP) or Microsoft Defender for Office 365.
SPF is often set up during domain onboarding, but DKIM and DMARC are frequently skipped, leaving organizations exposed to spoofing and impersonation. At the same time, many tenants don’t enable key anti-phishing features like Safe Links, Safe Attachments, impersonation protection, or disable risky features like automatic external forwarding.
Why it’s risky: Without proper email authentication, attackers can spoof your domain in phishing campaigns—tricking customers, partners, or employees into handing over credentials or money. Weak anti-phishing policies mean malicious emails are more likely to reach user inboxes, increasing the risk of successful BEC scams.
If auto-forwarding is enabled or malicious inbox rules go unmonitored, attackers who compromise a mailbox can quietly exfiltrate sensitive information or hide critical emails, sometimes for weeks or months before detection.
How to fix it:
p=none to monitor, then moving to quarantine or reject to block unauthorized senders.
Bottom line: Misconfigured email security in Microsoft 365 leaves the door open to phishing, spoofing, and silent data theft. By enabling authentication protocols and tuning anti-phishing settings, you can block the most common attack vector before it reaches your users—and avoid becoming the next BEC headline.
As this list shows, Microsoft 365 offers a wide range of powerful security features—but many of them require proactive configuration to be effective. Defaults aren’t always secure, legacy settings can linger unnoticed, and it’s easy to overlook risky gaps when managing a complex tenant. On top of that, Microsoft regularly adds new security controls, making it hard to keep pace without a systematic approach.
SaaS Security Posture Management (SSPM) solutions help security teams address these challenges by:
Nudge Security’s SSPM platform automatically detects common Microsoft 365 misconfigurations such as:
Start a free 14-day trial of Nudge Security to discover how SSPM can strengthen your Microsoft 365 security posture—and help you proactively reduce risk across your SaaS environment.
