picoCTF - Secret of the Polyglot

Posted on Jan 26, 2026
  • URL: https://play.picoctf.org/practice/challenge/423
  • Title: RED
  • Tags: Easy, Forensics, picoCTF 2024, file_format, polyglot
  • Author: SYREAL
  • Started: 15 July 2025
  • Solved: 15 July 2025
  • Description: The Network Operations Center (NOC) of your local institution picked up a suspicious file, they’re getting conflicting information on what type of file it is. They’ve brought you in as an external expert to examine the file. Can you extract all the information from this strange file? Download the suspicious file here.

After downloading flag2of2.pdf, my browser automatically showed the pdf

alt text

1n_pn9_&_pdf_53b741d6}

It was one part of the flag. According to the tag, I should check the file using file command

strikingsoul@ramones:~/Downloads$ file flag2of2-final.pdf 
flag2of2-final.pdf: PNG image data, 50 x 50, 8-bit/color RGBA, non-interlaced

It was actually a png! So I change the file extension and voila!

alt text

picoCTF{f1u3n7_

Combining those parts, I got

picoCTF{f1u3n7_1n_pn9_&_pdf_53b741d6}