Why do manual access reviews often fail to keep Microsoft 365 permissions under control?

Manual reviews are slow, inconsistent, and easy to delay when large user populations and frequent role changes are involved. Reviewers can miss risky access, apply decisions unevenly, or skip evidence collection. That creates entitlement creep and weakens governance. Regular certification with automation helps teams maintain control without relying on spreadsheet driven processes.

Why This Matters for Security Teams

Manual certification looks straightforward on paper, but Microsoft 365 environments tend to accumulate access through group sprawl, inherited permissions, service-linked identities, and rapid role changes. Once reviewers are faced with hundreds or thousands of entitlements, the process shifts from control to triage. That is why organizations increasingly pair reviews with the OWASP Non-Human Identity Top 10 and stronger lifecycle governance, because static spreadsheets do not reveal how permissions are actually used.

NHIMG’s research on 52 NHI Breaches Analysis and the Microsoft Midnight Blizzard breach shows the practical cost of weak identity oversight: once privileges linger, attackers and insiders alike can move through trusted workflows with little resistance. In Microsoft 365, that risk is amplified because permissions are often entangled with collaboration tools, mailboxes, SharePoint sites, Teams, and admin roles. In practice, many security teams discover entitlement creep only after an audit exception, a support ticket backlog, or an incident review has already exposed it.

How It Works in Practice

Effective access control in Microsoft 365 depends on understanding both direct assignments and inherited paths. Reviewers need to inspect group membership, privileged role activation, guest access, app consents, and stale service accounts, not just the visible user list. That is why current guidance from NIST SP 800-53 Rev. 5 Security and Privacy Controls emphasizes periodic review, least privilege, and evidence-backed authorization rather than informal approval loops.

In practice, a stronger model combines review automation with policy-driven workflows:

• Use entitlement discovery to map direct, nested, and inherited permissions across Exchange, SharePoint, OneDrive, Teams, and Entra ID.
• Classify access by business function, sensitivity, and admin impact so reviewers judge risk, not just possession.
• Trigger certification on events such as role change, department transfer, privileged elevation, or inactivity thresholds.
• Revoke or revalidate access automatically when a reviewer does not respond within a defined SLA.
• Log decisions with enough context to support audit evidence and exception handling.

That approach aligns with NHIMG’s Ultimate Guide to NHIs and Ultimate Guide to NHIs — Key Challenges and Risks, which both stress that identity governance fails when teams rely on manual memory instead of authoritative inventory. The key is not merely reviewing access more often, but making the review accurate enough to catch inherited privilege, stale collaboration access, and exceptions that were never meant to persist. These controls tend to break down when permissions are delegated across multiple tenants and business units because ownership and business justification become impossible to verify consistently.

Common Variations and Edge Cases

Tighter access reviews often increase operational overhead, requiring organisations to balance stronger governance against reviewer fatigue and slower business change. That tradeoff becomes most visible in Microsoft 365 when access is dynamic, shared, or tied to temporary collaboration.

Current guidance suggests a few edge cases need special handling. Guest users often have access that looks low risk until they inherit membership in high-value Teams or SharePoint sites. Privileged roles may be legitimately activated through just-in-time workflows, so a reviewer should validate the activation model rather than automatically revoking it. Service principals, automation accounts, and other non-human identities should not be forced into the same review cadence as end users, because their access may be narrow, technical, and tied to operational dependencies. Best practice is evolving here, but the direction is clear: treat each identity type by its function and risk.

For teams needing a practical starting point, NHIMG’s NHI Lifecycle Management Guide helps frame the full lifecycle, not just the certification event. The main failure mode is environments where permissions are granted through nested groups, external collaboration, and app registrations all at once, because no single reviewer can reliably see the complete entitlement chain.

Related resources from NHI Mgmt Group

• Why do manual access reviews often fail under public-market scrutiny?
• What breaks when organizations keep access control manual in modern identity environments?
• Why do manual access reviews often fail privacy and compliance audits?
• Why do manual access reviews fail to control privilege creep in mid-sized companies?