Microsoft Copilot for Word Can Copy Hidden Prompts Into New Documents

Researcher Håkon Måløy disclosed a technique where hidden instructions embedded in a Word document cause Microsoft 365 Copilot to rewrite content per the attacker’s instructions, then copy those same hidden instructions into the newly generated file.

In Måløy’s proof of concept, the resulting file triggered the same behavior in a second, separate Copilot drafting session, letting the injection self-propagate across documents. The finding was disclosed 144 days after being reported to Microsoft.