Around 80% of data breaches in organizations do not originate from sophisticated external attacks. They stem from internal errors: a forgotten share, an access right never revoked, a Teams group left in public mode. In Microsoft 365 environments, where Teams, SharePoint, OneDrive and Outlook multiply the channels through which data can be shared, this reality takes on a new scale. With the arrival of Copilot, it becomes urgent.
What this article covers:
Microsoft 365 was built to make collaboration easier. That is precisely what makes it fertile ground for M365 data oversharing. In a few clicks, a user can share a folder with the entire organization, invite an external contractor to a SharePoint site, or send a file via an anonymous link that anyone can access.
The problem is not the tool. It is the silent accumulation of permissions that no longer correspond to any operational reality.
Four channels coexist, each with its own permission logic: OneDrive for personal storage, SharePoint for collaborative spaces, Teams for conversations and project channels, Outlook for mailbox rules and delegations. None of these channels gives users a centralized view of what they have shared, with whom, and for how long.
Data exposure in Microsoft 365 does not result from a single cause. It builds up through recurring situations that IT teams know well, without always having the means to address them at scale.
First situation: unrevoked guest access. An external contractor works six months on a Teams project. The assignment ends, but the access remains active. Without a systematic review process, these obsolete accesses accumulate and represent as many potential entry points.
Second situation: overly broad internal shares. A “whole organization” link created quickly to share an urgent document stays active for years. A Teams group created in public mode by default exposes all its content to the entire directory.
Third situation: permission accumulation during internal mobility. When someone is promoted or changes roles, new rights are granted. The old ones are rarely revoked. The risk surface expands with every HR movement, without anyone noticing.
Fourth situation: anonymous shares with no traceability. An anonymous link requires no authentication. No identification rule applies, no access is tracked. If this link spreads beyond its original context, the data becomes accessible with no possible oversight.
Copilot does not create any new access rights. It strictly respects the permissions already in place across the M365 tenant.
That is precisely where the risk lies. Copilot scans all data a user has access to, including data they forgot existed long ago. An HR file shared with “the whole organization” three years ago, an M&A document accessible to an overly broad group, a financial report left in a public space: all of these can resurface in response to an innocent query.
Before Copilot, data exposure relied on a form of security through obscurity. Accessing sensitive information required knowing the folder structure, file names, and site hierarchies. Copilot removes that barrier. A natural-language query is enough to instantly surface and retrieve whatever the permissions allow.
96% of organizations report security concerns ahead of their Copilot deployment. This figure reflects a genuine shift in awareness: the issue is not the AI tool itself, but the state of the permissions it operates on. Microsoft itself recommends, before any Copilot deployment, identifying and remediating overshared sites, particularly those using “Everyone” or “Everyone except external users” sharing links.
Microsoft provides tools to address these risks: DLP policies via Purview, SharePoint Advanced Management data access governance reports, and Entra ID access reviews. These tools are useful. They also have concrete limitations in most deployments.
The first limitation is centralization. Users have no native interface to see all their active shares across OneDrive, Teams and SharePoint in one place. Visibility is fragmented by service, interface, and permission level.
The second limitation is scale. SharePoint Advanced Management DAG reports can identify overshared sites. But manually processing thousands of alerts across a tenant with several thousand users is not operationally viable for a standard-sized IT team. A tenant with 2,000 active users can generate thousands of at-risk configurations: no standard IT team can absorb that volume without dedicated tooling.
The third limitation is accountability. Native tools give visibility to administrators. They do not give data owners the means to remediate their own shares. Yet data owners are the ones who know the context: whether an access is still legitimate, whether an external share is still needed, whether a group can be closed.
Regaining control over Microsoft 365 data exposure does not require a long, expensive or IT-intensive project. It requires a structured approach, over a matter of weeks, that places accountability at the right level: with data owners.
The DETOX for M365 program, developed by IDECSI, is built on this principle. It runs in three steps over four to six weeks, with no infrastructure to deploy, delivered as SaaS.
The first step is a full tenant scan. The platform collects metadata (rights, shares, configurations) without ever accessing file content. It translates at-risk configurations into clear action points: active anonymous links, public groups containing sensitive data, unrevoked external access, overly permissive rights inherited from migrations.
The second step directly involves users. Each employee receives a notification and accesses their MyDataSecurity dashboard, which lists their action points. They remediate their own shares in one click, on the data they know best. IT supervises and can launch mass remediations on the most critical configurations in parallel.
Results are measurable. At Cergy-Pontoise agglomeration, 3,000 users, over 800 Teams: 50% of identified risks were eliminated in the first campaign. 70% in the second, six months later. Between the two campaigns, the volume of risks did not increase, signaling a lasting shift in user behavior.
"Thanks to IDECSI’s DETOX solution, we eliminated 1,796 risks from our data during our first campaign. Thanks to its user-friendly approach, users actively contribute to strengthening the cybersecurity of the Cergy-Pontoise agglomeration."
On average, across the full IDECSI client base, each user completes 7 remediations per campaign. The three most frequent actions: removing access, changing ownership, deleting an anonymous share.
This is not a one-time audit. It is a data hygiene practice that takes hold, renewed every six months, with results that compound over each cycle.
Data exposure in Microsoft 365 is a structural problem, not a situational one. It has built up over years, through thousands of routine sharing decisions that were never revisited. It cannot be solved by adding another security policy on top. It is solved by giving the right people, data owners, the visibility and tools to act.
With or without Copilot, taking back that control is a priority. With Copilot, it is a prerequisite.
To assess the state of your tenant in a few days, without burdening your IT team, contact IDECSI for a flash audit or register for the next webinar.