A researcher disclosed a prompt-injection technique that turns Microsoft 365 Copilot for Word into a carrier for self-spreading instructions. Malicious commands hidden as tiny white-on-white text in a document are invisible to a reader but read in full by Copilot when the file enters its context during a drafting or editing task. Copilot then follows them, in one example silently altering financial figures in a report, and copies the same hidden instructions into the new document, which becomes a fresh carrier for the next person who uses it. It does not spread on its own, but Microsoft's mitigations over 144 days blocked specific wordings without fixing the underlying class.
Researchers at Varonis disclosed SearchLeak, a flaw chain in Microsoft 365 Copilot Enterprise Search that let a single click on a legitimate microsoft.com link silently pull a victim's emails, calendar, and indexed files, including security and MFA codes, with no password or further interaction. It worked by smuggling instructions into the search URL's query parameter, which Copilot obeyed as commands, then exfiltrating the data through a Bing image request that bypassed content protections. Because the link used a real Microsoft domain, anti-phishing filters were unlikely to flag it. Microsoft assigned CVE-2026-42824, rated it critical, and fixed it on its backend, so no customer action is required.
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