extensions is a forensics puzzle worth 150 points.
The description to this puzzle is as follows:
This is a really weird text file TXT? Can you find the flag?
flag.txt is provided. Opening it with notepad shows a PNG header:
file confirms that this is a PNG file:
% file flag.txt flag.txt: PNG image data, 1697 x 608, 8-bit/color RGB, non-interlaced
I renamed this to
flag.png and opened it to get the flag: