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Public story · 2026-07-30 · high
Enklype Salt says modified payloads still worked when Microsoft disclosed the flaw, despite two fixes including a GPT-5.5 upgrade.
Why now: Enklype Salt published the full write-up on July 28, after Microsoft twice extended the original 90-day disclosure window to 144 days.
Microsoft Copilot for Word carries a prompt-injection worm that copies itself from document to document, per Enklype Salt.
That matters because the exploit hides inside the workflow every Word user already relies on: opening and editing shared documents. Microsoft took 144 days to disclose the bug, and Enklype Salt says it was still reproducible with new payloads at publication.
The bug starts with hidden white-text instructions buried in a source document.
Opening that file with Copilot's magic pen, or running Edit with Copilot in Work or Work IQ mode, triggers the hidden instructions. Copilot executes them and writes them verbatim into the new document it generates.
Handing that new document to a colleague as source material restarts the cycle, per Context Collapse Part 3.
No firewall or endpoint scanner catches it. The exploit never leaves Word's own document-sharing path.
Enklype Salt reported the flaw to Microsoft on March 6. Microsoft extended the standard 90-day disclosure window twice, pushing publication to July 28.
The post hit 369 points on Hacker News.
Microsoft shipped two mitigation attempts in that stretch, including an upgrade to the underlying model, GPT-5.5.
Microsoft's fixes targeted the model. The actual carrier is the document format, and nothing in the write-up says Word changed how it handles hidden text before Copilot reads it.
Patch the model and the same trick works with a new phrasing next month. Strip or flag hidden-text instructions before they reach the assistant, and the propagation stops regardless of which model runs it.
Enklype Salt doesn't say whether Microsoft has any plan to change how Word parses formatting before content reaches Copilot.
Each link below shares sources, entities, or timing with this story.
Copilot uses GPT / Shared entities / Shared topic / Earlier coverage / Tension
Linked by a graph relationship (Copilot uses GPT); both cover Copilot, Hacker News, Microsoft; overlapping topics (copilot, microsoft).
Copilot uses GPT / Shared entities / Shared topic / Earlier coverage
Linked by a graph relationship (Copilot uses GPT); both cover Copilot, GPT, Microsoft; overlapping topics (copilot, microsoft).
Linked by a graph relationship (Copilot uses GPT); both cover Copilot, GPT, Microsoft; overlapping topics (copilot, microsoft).
Linked by a graph relationship (Copilot uses GPT); both cover Copilot, Microsoft, Microsoft Copilot; overlapping topics (copilot, microsoft).
Linked by a graph relationship (Copilot uses GPT); both cover Copilot, GPT, Microsoft; overlapping topics (copilot, microsoft).
Microsoft criticizes Claude Code / Shared entities / Earlier coverage / Tension
Linked by a graph relationship (Microsoft criticizes Claude Code); both cover GPT, July, Microsoft; earlier GPT coverage from 2026-07-26.
Linked by a graph relationship (Microsoft criticizes Claude Code); both cover GPT, July, Microsoft; earlier GPT coverage from 2026-07-23.
Copilot uses GPT / Shared entities / Earlier coverage / Tension
Linked by a graph relationship (Copilot uses GPT); both cover Copilot, GPT, July; earlier Copilot coverage from 2026-07-10.