MisuseSerious1 sourceFirst seen
Copilot Cowork's Sandbox Bypass Hands Attackers the Keys to Your Inbox and SharePoint
Ourtake
A document comparison turned into a remote control channel, and the stop button did not stop it.
What happened
Researchers at PromptArmor found that a sandbox bypass in Microsoft Copilot Cowork let a malicious script inside a user-uploaded Skill reach attacker servers. The attacker could run commands and exfiltrate data from Outlook, SharePoint, Teams, plugins and chat history. The issue was reported to Microsoft on June 24, 2026 and confirmed mitigated on August 19, 2026.