Microsoft Copilot Cowork Exfiltrates Files via Prompt Injection

Originally published on PromptArmor — May 25, 2026

Summary

Security researchers at PromptArmor demonstrated that Microsoft Copilot Cowork, a Frontier M365 feature, is vulnerable to file exfiltration via indirect prompt injection. By exploiting insecure automatic action approvals for emails and Teams messages, attackers can steal pre-authenticated file download links from SharePoint and OneDrive. The attack achieved a high success rate against state-of-the-art models including Claude Opus 4.7, highlighting the expanded attack surface of agentic AI systems.

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