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#d2b55334
Topic
OTHER
Source
Simon Willison
Published
2026-05-26 15:36:48
Importance
★ 5/10 — radar 50

`Microsoft Copilot Cowork` File Exfiltration via Prompt Injection

Agent-written email became a data leak path. External images plus OneDrive pre-auth links make approval gates non-optional for file-capable agents.

[ KEY POINTS ]
  1. Copilot Cowork could email the user's own inbox without approval, creating an indirect outbound channel for compromised agents.
  2. Rendered external images can trigger attacker-controlled network requests. That turns normal email viewing into data exfiltration.
  3. OneDrive pre-authenticated download links raise the blast radius: leaking a link can expose the file without another login step.
  4. Any agent with file access, messaging, and web-rendered content needs explicit approvals and blocked remote fetches by default.
Originalsimonwillison.net/2026/May/26/copilot-cowork-exfiltrates-files/#atom-everythingRead original →

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