The Engine Room: Microsoft Graph
Before we get to the specific permission, it's crucial to understand what Microsoft Graph is. Think of it as the central nervous system for your entire Microsoft 365 environment. It’s an API—an application programming interface—that connects all the data
floating around in services like SharePoint, Teams, Outlook, and OneDrive. Copilot uses Microsoft Graph to find and synthesize information to answer a user's prompt. When someone asks Copilot to summarize project updates, it's Graph that fetches the relevant emails, Teams chats, and documents. This is the source of Copilot's power, but it's also where the security risks begin.
The Permission That Changes Everything
The headline permission isn't a user permission, but an application permission. While there are several powerful ones, security experts frequently point to `Sites.Read.All` as a major concern. This permission, when granted to an application or a custom-built Copilot extension, allows it to read all content on every single SharePoint site in your organization. This is different from the standard Copilot model, which operates within the permissions of the signed-in user. Where a custom app or connector has been granted `Sites.Read.All`, it acts with its own authority, independent of who is asking the question. This creates a potential blind spot for security teams.
Why 'Read-Only' Is So Risky
The term 'read-only' can sound harmless, but in the context of `Sites.Read.All`, it's a significant threat. Most organizations have years of what security pros call 'permissions debt' or 'SharePoint sprawl'. This includes old, forgotten sites for mergers and acquisitions, legacy HR investigations, or executive salary planning. While a human employee would likely never stumble upon these files, an AI armed with tenant-wide read access can find them instantly. Copilot doesn't break permissions; it industrializes the discovery of existing ones that are overly broad. A casual prompt from an unauthorized user could inadvertently surface highly confidential data if the underlying permissions allow it.
The Real Problem: Oversharing
Ultimately, the risk isn't from Copilot or even the `Sites.Read.All` permission in isolation. The root cause is years of unchecked data sharing. Security reports show that a significant percentage of business-critical data is 'overshared'—accessible to larger groups than necessary, often through default settings like 'Everyone except external users'. Copilot acts as a high-speed searchlight on these existing vulnerabilities. Before AI, security through obscurity was a fragile, accidental defense. Copilot removes that obscurity entirely, making proactive data governance an urgent necessity.
Your Counter-Move: Least Privilege and Audits
The solution is to adopt a 'least privilege' model. This security principle dictates that any application or user should only have the absolute minimum permissions necessary to perform its function. Instead of granting sweeping `Sites.Read.All` access, IT and security teams should challenge why it's needed. For custom integrations, Microsoft Graph allows for more granular permissions, like `Sites.Selected`, which restricts access to a specific list of approved SharePoint sites. The rollout of Copilot should be a trigger for a full audit of your Microsoft 365 permissions. Identify and remediate overshared sites, apply sensitivity labels to classify data, and establish clear ownership for all data repositories.
