Microsoft Copilot Can Surface Overshared Data Despite Permission Boundaries

Microsoft Copilot respects existing user permissions when retrieving data from Microsoft 365 services, yet the feature can still expose more information than administrators expect because of permissive default sharing settings.

According to official Microsoft pages, the assistant only accesses content the signed-in user is already authorized to view. The documentation explicitly states that operating inside the Microsoft 365 boundary does not grant tenant-wide visibility and that the semantic index honors identity-based access boundaries.

However, the same guidance notes that SharePoint sets sharing settings to the most permissive option by default. This combination means Copilot will faithfully surface documents, emails, and Teams conversations that were once shared broadly and then forgotten.

Microsoft refers to this scenario as accidental oversharing and recommends adjusting SharePoint and OneDrive sharing settings before enabling the assistant. Administrators are advised to run the Content Management Assessment tool to identify potentially overshared content and to review Data access governance reports, particularly the “Everyone except external users” report that lists the top 100 sites shared organization-wide in the past 28 days.

Two controls help limit exposure. Restricted Access Control uses groups to block all access to a site, including previously granted permissions. Restricted Content Discovery prevents content from appearing in Copilot responses and organization-wide search while leaving existing permissions unchanged, making it easier to obtain approval from data owners.

When data is protected by Microsoft Purview sensitivity labels or Information Rights Management, Copilot honors the granted usage rights. Encryption settings can also exclude programmatic access, thereby limiting what agents can read, although Microsoft documentation stops short of promising complete blocking of file access.

Every Copilot interaction stores the user prompt, the generated response, and citations to source documents. These records can be reviewed through Content search or Microsoft Purview, turning potential oversharing risks into concrete lists of accessed files.