Malicious Copilot Cowork skill hijacked AI gateway to exfiltrate files

PromptArmor disclosed that a malicious Skill could hijack Copilot Cowork's AI gateway to spawn cloud agents that exfiltrate a victim's files to an attacker's server. No human approval was required, and any data Copilot could access was exposed. The vulnerability was reported to Microsoft on July 14, 2026, and Microsoft confirmed a fix on September 2, 2026.