Detecting Hidden Instructions in PDF Extraction PipelinesDetecting Hidden Instructions in PDF Extraction Pipelines
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Most PDF extraction pipelines would have missed the Brazilian court-filing injection.
Two law firms hid white-on-white text in a labor court petition. It told the court's AI reviewer to answer superficially and not challenge the documents. The court's tool, Galileu, flagged it and blocked it, and the court fined the firms 10% of an R$842,000 claim.
Most of the Hacker News thread blames the court for running AI on filings. But the trick works on any pipeline that reads PDFs. White text is invisible on the page and still sits in the text layer, which is what gets extracted.
My extraction pipelines check each field against the page it came from. That catches a wrong value, but not an instruction that changes how the model reads the rest of the file. That needs a check before the model sees anything: text a person can't see on the page shouldn't reach the model.
In the PDFs you extract from, how often does the text layer hold something the page doesn't show?
Joe's avatar
Source: https://jetstream.security/insights/brazilian-court-sanctions-prompt-injection-filing
Huzaifa's avatar
White-on-white instructions in a PDF text layer is exactly the failure mode I watch for in clinical intake. Referral packets and lab PDFs often carry junk from fax OCR or prior template text that a model will treat as orders. I would strip or quarantine any span whose rendered...
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