Before You Deploy Copilot for Microsoft 365: What IT Admins Need to Fix First
How Copilot accesses your data
👤
User
sends prompt
✨
Copilot
inherits permissions
📁
All content
user can access
including
⚠️
Overshared content
overexposed content
Copilot does not verify whether access was intended — only whether it is permitted.
TL;DR
- The core problem: Copilot inherits every user's permissions. If your SharePoint is overshared, your sensitivity labels are missing, or your DLP is in audit mode, Copilot can surface data that is overly exposed through existing permissions — content that was technically accessible but practically out of reach before AI-assisted search.
- The key risk: SharePoint oversharing is consistently flagged as the top Copilot security concern — described broadly as "a known risk amplified by AI." It is the issue I see most often when reviewing tenants preparing for Copilot deployment.
- What this article covers: The five controls you need to validate before activating Copilot — identity, permissions, data classification, DLP, and monitoring.
- The bottom line: Copilot is a productivity tool built on top of your data governance. If the governance isn't there, the productivity gain comes with a data exposure risk that scales with every user you enable.
🚨 Recent Vulnerability — Patched March 11, 2026
As an example of an emerging class of AI-specific risks, Microsoft addressed a cross-prompt injection vulnerability in Copilot in early 2026. Tenant configuration remains a more durable control than patch cadence alone.
Five Security Risks Worth Addressing Before Deployment
The following risks reflect a combination of patterns I observe in tenant assessments and topics actively discussed in the M365 security community in 2026. This is not an exhaustive or official list — it's a practical framing of the areas most worth validating before you activate Copilot.
RISK 01 — CRITICAL
SharePoint Oversharing
The most consistently discussed Copilot security risk. Copilot can search and surface any SharePoint content the user has access to — making overly broad permissions far more accessible than they were before.
RISK 02 — CRITICAL
Prompt Injection Attacks
Malicious content embedded in documents, emails, or SharePoint pages may attempt to influence Copilot's output — a pattern known as prompt injection. Microsoft has disclosed at least one vulnerability in this category (addressed March 2026). Built-in content filters help mitigate this, but awareness of the risk class is worthwhile when planning your deployment.
RISK 03 — HIGH
Sensitive Data Exposure via Third-Party Apps
Copilot can surface sensitive data when users link it to third-party SaaS applications. The third-party application plugin is off by default — but the web content plugin is enabled. Review both before deploying.
RISK 04 — HIGH
Risks from Ungoverned AI Experimentation
Organisations giving users broad Copilot access without governance or acceptable use guidance may inadvertently increase their exposure to prompt-based risks. Using Copilot's built-in content filters and establishing clear guidance on what data should and shouldn't be referenced in prompts helps reduce this surface.
RISK 05 — MEDIUM
Toxic or Inappropriate Output
Copilot can produce output that is factually correct but culturally or professionally unacceptable. All Copilot output requires review before sharing. Xu's half-serious recommendation: consider restricting Copilot use on Friday afternoons when user attention is lowest.
PRACTICAL TAKEAWAY
No Single De-Risking Layer Exists Yet
There is currently no single setting or toggle that addresses all Copilot security risks simultaneously. The controls in this checklist are the closest practical equivalent — each one reduces a specific, addressable exposure area.
01 — Identity & Access Foundation
- MFA enforced for all users — not just adminsIf Copilot is activated on a compromised account, an attacker gets access to an AI assistant that can summarise and surface your entire content library. MFA via Conditional Access for all users is the baseline gate before any AI feature is enabled.
- Conditional Access policy for Copilot accessConsider creating a CA policy specifically for Copilot that requires a compliant device and enforced MFA. Copilot on an unmanaged personal device with no compliance check is a data exfiltration risk that didn't exist before AI.
- Entra ID Protection risk policies activeA high-risk sign-in should automatically block or step up access — including to Copilot. Without risk-based CA, a compromised credential gets access to your AI-powered content discovery engine.
02 — SharePoint & OneDrive Permissions Audit
This is the highest-impact step. Before you enable Copilot, you need to understand what your users actually have access to — not what you think they have access to. Microsoft provides a structured deployment blueprint (Pilot → Deploy → Operate) where the Pilot phase is explicitly dedicated to discovering and remediating oversharing before Copilot is scaled. The primary tool for this is the Data Access Governance (DAG) report in the SharePoint Admin Center — a built-in report that shows which sites are broadly accessible and to whom.
- Run Data Access Governance reports in SharePoint Admin CenterGo to SharePoint Admin Center → Reports → Data access governance (Microsoft docs ↗). Run the "Sites with 'Everyone except external users'" report and the "Oversharing" permission state report. These tell you exactly where broad access exists across your tenant.
- Change the default sharing link from "Anyone" to "Specific people"In SharePoint Admin Center → Policies → Sharing, change the default sharing link type for both SharePoint and OneDrive from "Anyone" or "People in your organisation" to "Specific people". This doesn't fix existing shares — but it stops new ones from defaulting to broad access.
- Use Restricted Content Discovery to block Copilot from overshared sitesSharePoint Advanced Management (available as an add-on or included with certain M365 Copilot licences) provides Restricted SharePoint Search and site-level controls that can limit what Copilot and search surface from specific sites (Microsoft docs ↗). Use this as a temporary measure while you remediate the underlying permissions on high-risk sites.
- Initiate Site Access Reviews for high-risk sitesFor sites flagged as overshared, use the Site Access Review feature to notify site owners and ask them to confirm or remediate permissions. Site owners know the business context — you don't have to review every site manually.
- Archive or delete inactive sitesSites moved to Microsoft 365 Archive are not accessible by Copilot. Identifying and archiving inactive sites reduces your Copilot data surface immediately — and improves Copilot response quality by removing stale content from its index.
⚠️ The "Everyone Except External Users" Problem
The most common oversharing pattern I find in SMB tenants is content shared with "Everyone except external users" — a group that includes every single person in your Microsoft 365 tenant. Copilot can treat this as eligible content to surface for any user whose access permissions include that site. Run the DAG report first. The number of files in this category is almost always a surprise.
03 — Data Classification & Sensitivity Labels
Sensitivity labels are one of your most important tools for data classification — and they are directly relevant to Copilot. Without them, classification context is absent — a contract, an HR file, and a project brief look the same from a data governance perspective, making it harder to apply differentiated controls. With labels applied and the right protection settings configured, you can significantly influence what Copilot surfaces and to whom. The exact behaviour depends on how labels and Copilot are configured in your tenant, so treat labels as a foundational layer, not a complete access control.
- Deploy a sensitivity label taxonomy before Copilot goes liveAt minimum: Public, Internal, Confidential, Highly Confidential (Microsoft docs ↗). When configured correctly, sensitivity labels can help restrict what Copilot surfaces in responses — for example, limiting access to Highly Confidential content based on label-based protection settings. Labels without this configuration provide classification context, but may not restrict AI-surfaced access on their own.
- Enable auto-labelling policies for sensitive content typesManual labelling doesn't scale. Configure auto-labelling in Microsoft Purview to detect and classify content containing credit card numbers, national IDs, IBAN numbers, or other sensitive data patterns — and apply the appropriate label automatically across SharePoint, OneDrive, and Exchange.
- Apply site-level sensitivity labels to high-risk SharePoint sitesSite labels restrict sharing behaviour and set a baseline classification for all content on that site. A site labelled Confidential can restrict sharing behaviour — depending on how the label is configured, it may prevent content from being shared broadly. Verify your label settings in Microsoft Purview to confirm the exact enforcement behaviour for your configuration. Use this for legal, HR, finance, and executive sites before Copilot is enabled.
- Use DSPM for AI to run a data risk assessmentMicrosoft Purview's Data Security Posture Management for AI (Microsoft docs ↗) runs periodic assessments on your most active SharePoint sites. It surfaces unprotected sensitive files and gives you policy suggestions before you scale Copilot. Run this before your pilot group is activated.
04 — Data Loss Prevention for AI
- Move DLP policies from Audit to Enforce mode before deploymentDLP policies in audit mode generate alerts but do not block the action. When switched to enforce mode, matching interactions may be blocked depending on the rule configuration. Audit mode provides visibility — enforce mode provides control. Review your DLP policies and move the most critical ones to enforce mode before scaling Copilot access.
- Extend DLP policies to cover Copilot interactionsMicrosoft Purview DLP can be configured to detect sensitive information types in Copilot prompts and responses (Microsoft docs ↗). This requires enabling the Copilot scope within your DLP policy — it is separate from traditional workload scopes like Exchange, SharePoint, and Teams. Verify your DLP policies explicitly cover Copilot and agent interactions — not just email, SharePoint, and Teams.
- Note: labels alone are not enough if the underlying site is oversharedThis is a critical caveat from Microsoft's own documentation. If labelled data sits in an overshared SharePoint site or Teams channel, it is still accessible to everyone who has access to that site. Sensitivity labels protect the file in transit — they do not fix underlying permission problems. Fix the permissions first.
05 — Monitoring Copilot Activity
-
Enable Copilot interaction logging in the Unified Audit LogCopilot prompts, responses, and referenced files are captured in the Unified Audit Log under the
CopilotInteractionevent type (Microsoft docs ↗). This is your forensic record of what Copilot surfaced, for whom, and when. Verify the audit log is enabled and retention is extended beyond the 90-day default for regulated environments. - Use DSPM for AI to monitor Copilot interactions with sensitive contentMicrosoft Purview DSPM for AI provides reports on sensitive data and unprotected files referenced in Copilot and agent interactions. This is your ongoing visibility layer — not just a pre-deployment check. Run it regularly after Copilot is live.
- Disable the web content plugin if not requiredThe third-party application plugin for Copilot is off by default — the web content plugin is on. If your users don't have a business need for Copilot to query external web content, disable this in the Microsoft 365 admin center. It reduces the prompt injection attack surface from external sources.
- Define an acceptable use policy for Copilot before rolloutUsers need to understand that Copilot output requires review before sharing, that prompts may surface unexpected content, and that inputting sensitive client data into prompts carries data governance implications. An acceptable use policy isn't bureaucracy — it's the governance layer that patches the human vector.
Recommended Copilot deployment sequence
ℹ️ What This Checklist Does Not Cover
This checklist focuses on the controls most directly relevant to Copilot security posture. Some advanced capabilities — such as DSPM for AI at full depth, Copilot agent governance, and Microsoft Sentinel integration for AI activity monitoring — go beyond what is covered here. The checklist above is the baseline. The full governance picture is larger.
🔍 Before You Enable Copilot
The most useful thing you can do right now is run the Data Access Governance report in your SharePoint Admin Center and look at the results honestly. Most of the time, that report alone changes the conversation about deployment readiness. If you work through the findings and want a second perspective — or if you'd find it useful to map the checklist against your specific tenant configuration — feel free to get in touch.
📚 Related Articles
The controls in this checklist are covered in detail across this blog: