Microsoft 365 Copilot Security
Permissions inheritance is the central security model. Get that wrong and Copilot surfaces what your SharePoint sprawl never made visible.
- Vendor
- Microsoft
- Product
- Microsoft 365 Copilot
- Guide covers
- Central risk, specific risks, recommended controls, and your Posture Check checkpoint
What it is
Microsoft 365 Copilot is the AI assistant integrated across Microsoft 365 applications (Word, Excel, PowerPoint, Outlook, Teams, OneNote). It uses large language models grounded in the user's Microsoft Graph context (emails, documents, chats) to generate responses scoped to what that user technically has access to.
The central risk
Permissions inheritance. Copilot does not bypass permissions; it inherits them. If Charlie has access to a SharePoint folder he never opened, Copilot will surface its contents in response to questions. The security problem moves from access control (which was already lax) to discovery. Copilot makes discovery one prompt away.
Specific risks in Microsoft 365 Copilot
Latent over-sharing surfaced through prompts
Sensitive content embedded in documents (PII, secrets, confidential strategy) becoming queryable
Audit-trail gaps: Microsoft Purview captures Copilot interactions only if licensed and configured
Prompt injection through documents and emails (indirect LLM01)
Output handling in downstream automation (LLM05)
Recommended controls
Run a permissions audit before Copilot rollout: scope reduction, group cleanup, label enforcement
Deploy Microsoft Purview labels and DLP. Without these, content classification is ineffective
Enable Microsoft 365 Audit logging at the appropriate tier (E5 or M365 E5 Compliance)
Communicate user expectations. Copilot will surface what you have access to, including content you forgot you had
Test Copilot with adversarial-prompt scenarios specific to indirect injection
Score yourself before you roll out Microsoft 365 Copilot.
The AI Posture Check is a free five-question adaptive self-assessment that maps your gaps to specific OWASP LLM Top 10 risks for Microsoft 365 Copilot.
Take the AI Posture Check before rolling out Copilot to see where permissions hygiene puts you: Crawl, Walk, Run or Sprint.
Take the AI Posture CheckGet a Standard Audit on your Microsoft 365 Copilot deployment.
A senior CWS engineer reviews your specific deployment, runs adversarial tests, and produces a remediation roadmap.