│ Category: Miscellaneous
│ Author: Imattas aka Zemi
│ Flag: byuctf{wh4t_th3_fr3ak}
│ Source Path: misc/inception
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--[ Challenge Description ]--
-- text --
Title: Inception
Description: I found this weird file on my computer. I tried opening it, but there were some problems.
Files: inception
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--[ Provided Materials ]--
- Repository folder
https://github.com/BYU-CSA/BYUCTF-2026/tree/main/misc/inception
- misc/inception/challenge.md
https://github.com/BYU-CSA/BYUCTF-2026/blob/main/misc/inception/challenge.md
- misc/inception/writeup.md
https://github.com/BYU-CSA/BYUCTF-2026/blob/main/misc/inception/writeup.md
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--[ Recon / Initial Analysis ]--
This page imports the BYUCTF 2026 source material for the Miscellaneous
challenge Inception. The prompt is kept separate from the solve notes, and
upstream artifacts are linked so the challenge can be replayed from the original
repository.
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--[ Vulnerability / Observation ]--
The useful observation comes from the imported solve notes below. I kept the
original technical path intact while normalizing the page metadata, challenge
grouping, and author attribution for the Volume 2 writeup archive.
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--[ Exploitation / Solution ]--
Source: misc/inception/writeup.md
https://github.com/BYU-CSA/BYUCTF-2026/blob/main/misc/inception/writeup.md
The general idea for this challenge is that the file in question is a Polyglot
file (https://en.wikipedia.org/wiki/Polyglot_(computing)). This means that the
file is technically multiple different file types, that are all valid and can be
parsed correctly. In this case, the challenge file is simultaniously a .png, a
.zip, and a .pdf file.
--[ Step 1 ]--
To start, the file has no extention and no instructions. The first move on any
unknown file is to run file and strings:
-- bash --
$ file inception
inception: PNG image data, 273 x 160, 8-bit/color RGB, non-interlaced
It's a PNG. Open it in any image viewer and you'll find part one of the flag.
strings won't reveal much — the interesting content has been stripped or
compressed — but a more thorough recon tool will:
-- bash --
$ binwalk inception_challenge.bin
DECIMAL HEXADECIMAL DESCRIPTION
--------------------------------------------------------------------------------
0 0x0 PNG image, 525 x 160, 8-bit/color RGB, non-interlaced
1187 0x4A3 Zip archive data, at least v2.0 to extract
1483 0x5CB End of Zip archive
1561 0x619 PDF document, version 1.4
At this point its clear that there are some strange things happening in the
file. The file reports a PNG, a Zip archive, and a PDF.
--[ Step 2 — Extract the ZIP ]--
ZIP archives store their directory index at the end of the file, so unzip can
read the archive even with a PNG prepended to it.
-- bash --
$ unzip inception_challenge.bin
Archive: inception_challenge.bin
warning [inception_challenge.bin]: 1187 extra bytes at beginning or within zipfile
(attempting to process anyway)
inflating: data.bin
$ cat data.bin
This gives you part two of the flag.
--[ Step 3 — Extract the PDF ]--
PDF readers scan backwards from the end of a file looking for %%EOF, so the PDF
is valid despite being appended after the PNG and ZIP data. Open it in any PDF
viewer, or extract the text directly:
-- bash --
$ pdftotext inception_challenge.bin -
This gives you part three of the flag.
Flag: byuctf{wh4tth3fr3ak}
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--[ Full Exploit Script ]--
No standalone exploit script was present in the selected source material.
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--[ Key Takeaways ]--
- The BYUCTF 2026 challenge material is preserved with local archive formatting.
- The page author is normalized to Imattas aka Zemi.
- The source repository remains linked for handouts, services, and solve
artifacts.