Security1 hOctober 29, 2026, 06:34

MuPDF before 1.28.5 had only 9 bits of entropy in its AES-256 key

V12 researchers found that MuPDF before 1.28.5 derived its PDF file key from drand48 seeded with the current time in seconds, leaving just 9 bits of entropy. Brute-forcing all 512 candidates takes about 9 ms; similar flaws were found in Foxit, OpenPDF and iText.

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MuPDF before 1.28.5 had only 9 bits of entropy in its AES-256 key

MuPDF seeded drand48 with time in seconds, reducing the key to 512 values
Enumerating the whole keyspace took 8.7 ms, faster than opening the PDF
Foxit hashes the current second plus a constant: 10 years of timestamps in 0.84 s
MuPDF 1.28.5 switched to a real CSPRNG; older files remain exposed

#MuPDF#Foxit#PDFium#IText

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