When Microsoft 365 security incidents occur, they are often attributed to “sophisticated attacks” or “advanced threat actors”. In reality, the majority of compromises exploit well-known, repeatable misconfigurations that have existed quietly for months or years.
These issues persist not because they are difficult to fix, but because they sit in the gaps between responsibility, ownership, and visibility.
This article outlines the most common Microsoft 365 misconfigurations we encounter, why they matter, and why they are so persistent.
What makes these misconfigurations particularly dangerous is that they often arise in environments managed by capable, well-intentioned teams. They are not the result of ignorance or neglect, but of competing priorities, inherited decisions, and a lack of sustained visibility. Over time, these factors combine to create security gaps that feel normal internally, even as they represent significant exposure externally.
Zero-day vulnerabilities attract headlines. Misconfigurations cause breaches.
From an attacker’s perspective, misconfiguration is vastly more attractive than exploiting software flaws. It requires less effort, carries less risk, and scales easily across environments. A single technique can be reused repeatedly against tenants that are configured in broadly similar ways. This predictability is what makes misconfiguration such a reliable entry point.
Attackers targeting Microsoft 365 overwhelmingly prefer:
Misconfiguration provides all three.
Because misconfigurations do not announce themselves as “broken”, they often escape normal operational scrutiny. There is no failed service, no patch advisory, and no obvious incident to trigger investigation. In many cases, the configuration is working exactly as intended — just not as securely as assumed:
Over time, they become normalised.
Excessive privilege is one of the most damaging and common issues.
Typical causes include:
Privilege creep is rarely the result of a single poor decision. It accumulates incrementally as access is granted to solve immediate problems, support growth, or respond to incidents. Once established, excessive privilege becomes difficult to unwind without disrupting operations or challenging entrenched expectations. This inertia is what allows dangerous access patterns to persist long after their original justification has disappeared.
Once privilege creep sets in, attackers need only compromise a single account to gain extensive access.
Guest access is essential for collaboration — and a frequent source of exposure.
Common issues include:
In many tenants, guest users persist indefinitely, quietly expanding the attack surface.
The risk posed by external users is not limited to what they can access today, but how little visibility organisations retain over time. Guest accounts often fall outside normal user lifecycle processes, meaning they are rarely reviewed, rarely challenged, and rarely removed. As business relationships change, these accounts quietly become detached from their original context, turning collaboration into long-term exposure.
Audit data is often misunderstood.
We frequently encounter tenants where:
Weak audit logging does not usually attract attention until something goes wrong. At that point, organisations discover that they cannot reliably answer basic questions about who accessed what, when, and how. Investigations become speculative, incident timelines remain incomplete, and confidence in conclusions erodes. The absence of sufficient audit data turns manageable incidents into prolonged crises.
Data Loss Prevention is often deployed optimistically:
As a result, policies generate noise, true data leakage goes unnoticed and alerts are ignored, DLP without operational ownership becomes a compliance artefact rather than a security control.
Data Loss Prevention is particularly vulnerable to this pattern because it sits at the intersection of technology, user behaviour, and business context. Without clear ownership and ongoing tuning, DLP policies either become overly permissive to avoid disruption or overly noisy to the point of irrelevance. In both cases, the control exists in name but fails to meaningfully reduce risk.
These misconfigurations persist because:
Many of these issues persist because they do not map neatly to team boundaries. Identity, data protection, logging, and external access often span multiple functions, each with partial responsibility but limited end-to-end ownership. In the absence of clear accountability, problems are acknowledged but not resolved, gradually becoming accepted characteristics of the environment.
They are not failures of competence — they are failures of visibility.
The danger of familiarity is that it dulls urgency. When the same misconfigurations are observed repeatedly without immediate consequence, they cease to feel risky. Over time, organisations begin to optimise around them rather than challenge them, embedding insecurity into everyday operations.
The most dangerous Microsoft 365 security issues are not novel. They are familiar, well-documented, and often quietly accepted.
Familiarity breeds comfort, not safety.
What distinguishes mature organisations is not the absence of misconfiguration, but the willingness to surface and challenge it. Independent review turns “this is how it’s always been” into “this is what actually matters”.
Misconfiguration is inevitable. Unchecked misconfiguration is optional.
Trusted Microsoft Cloud Security Advisor with 27 years experience | Empowering Businesses to Embrace Cloud Innovation with Confidence
