Extensions 🚩

Point: 150

Category

Forensics

Question

This is a really weird text file TXT? Can you find the flag?

Hint

How do operating systems know what kind of file it is? (It’s not just the ending!

Make sure to submit the flag as picoCTF{XXXXX}

Solution

This challenge is fairly simple if you know how file extensions work in different operating systems. One line explanation of file extensions is: it is a tag for an operating system to interpret and run the file using their respective programs. E.g: files with pdf extension can be run using a pdf reader.

There is a really good in-depth explanation on this by LiveOverFlow which I highly recommend watching. https://youtu.be/VVdmmN0su6E

With that being said, here’s how I approached the problem.

wget https://jupiter.challenges.picoctf.org/static/e7e5d188621ee705ceeb0452525412ef/flag.txt

file flag.txt
flag.txt: PNG image data, 1697 x 608, 8-bit/color RGB, non-interlaced

From here, we can find that the original file format is PNG image data. We can change the extension as below.

cp flag.txt flag.png

open flag.png

The flag can be found using an image viewer.

Improvement

None

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