Hidden text injection in PDF bypasses security stack, exposing multi-channel blind spots
WolfShoddy7443 · reddit · 2026-08-24
A user shared a security incident involving hidden text prompt injection in a PDF:
- An attacker injected hidden instructions in a contract footer; the model caught it, but the org's security stack (monitoring only chat inputs) remained silent.
- Attack vectors are expanding to files, emails, calendar invites, and any content the model can access.
- Security advice: Monitor all input channels, not just the user chat box.
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