Our goal is to retrieve the hidden flag hidden somewhere inside the PDF. $ file 18pages.pdf 18pages.pdf: PDF document, version 1.7
To be thorough, we also checked whether any other objects contained additional base‑64 or XOR‑encoded data, but none yielded a flag. 18 Pages Hdhub4u
Category: Steganography / Forensics – PDF 1. Overview The challenge consists of a single file named 18pages.pdf (≈ 1 MB). The description on the challenge page simply says “18 Pages – Hdhub4u” and a point value of 300. Our goal is to retrieve the hidden flag
A quick visual check shows a fairly clean document – a title page, a table of contents, and then a series of “chapter‑style” pages full of lorem‑ipsum text. Nothing suspicious at first glance. PDFs are made of a series of objects (streams, dictionaries, etc.). Hidden data is often stored in unused objects, extra streams, or in the metadata section. Overview The challenge consists of a single file
$ pdf-parser -dump 18pages.pdf > pdf_objects.txt The dump revealed the following interesting points:
$ pdfinfo 18pages.pdf Title: 18 Pages Creator: LaTeX with hyperref Producer: pdfTeX-1.40.21 CreationDate: D:20260312123456-04'00' ModDate: D:20260312123500-04'00' Tagged: no Pages: 18 Encrypted: no Page size: 595.276 x 841.89 pts (A4) The file looks like an ordinary PDF with (as the title hints).