Swati KhandelwalJul 30, 2026Vulnerability / AI Security
Hidden instructions in a Word document can make Microsoft 365 Copilot rewrite figures in a report, then copy the same instructions into the finished file. Håkon Måløy disclosed the technique on July 28, 144 days after reporting it to Microsoft.
In his proof of concept, the internally generated file triggered the same behavior when it was used in a second Copilot drafting session.
Måløy's timeline says Microsoft confirmed the reported behavior on March 31 and deployed two mitigations. The first blocked the original prompt wording; the second upgraded the underlying model to GPT-5.5.
He said the full chain worked with modified instructions on GPT-5.6 the next day, and the attack class still reproduced on July 28. "The vulnerability class therefore remains exploitable at the time of publication," Måløy said.
