Homemade CTF Challenge: 06 "A Brisk Stroll"

welcome back everyone I wanted to Showcase more of the local CTF or Capture the Flag competition that I put together as practice as like a local exercise for my uh my my school and at Cyber team so this challenge I want to show off is the brisk stroll or uh a Brisk stroll and the prompt is have you seen this image before there is no hint for this one but the file name is a walk with the numbers St PNG so you would go ahead and download this and I'll zoom out here you'll see that is a picture and the ploy or the hope is that they'd go ahead and save this picture and the hint that uh have you seen this before is hey if you haven't already if you if you haven't seen it you can do a Google reverse image search to go ahead and find where it comes from so uh obviously you I guess if you wanted to not knowing you would want to do a little bit of stenography on the thing you can you could run a exf tool on a with the numbers you could run strings on it um but it is it is just a regular image file I didn't I didn't try to pull any tricks with that however what I did do is I added more to it so if we did that Google image search Total fail um we could upload that walk with the numbers that we just uploaded and then it will keep looking for us and it will note that that oh it looks like atmosphere okay there's a there's a red herring there but pages that include this image oh it says binwalk for mac and Linux oh binwalk comments oh binwalk for more analysis tool very clearly I would hope binwalk is uh what they would be pointed to if they had not seen this or or have known of this tool before so at that point you would end up installing or working with binwalk and I would recommend running binwalk on that file and hey it notices there the image of course the ZB compress data is a fault that benok tends to do and it also sees a program in there which is interesting so uh we can run binw walk- e to extract stuff out of it and we would run it on the walk with the numbers and now we see that extracted folder so we can CD into that and it sees this elf file so that's got to be executable so we could run could run that thing and there it is we get our flag cool uscga binwalk is a good tool to know so we'll submit that and get our points and I'll show off how I actually put that together so it's real simple um what I ended up doing for one thing was writing out the source code for this program which is again insanely simple it literally just prints out the flag um and then I think I put together a create. sh where I would compile the file make it 32-bit compile that source code and then I'd include the image the original image which is just that simple picture and then I'd include that who put this here executable that I just compiled and I just created and then I put it in that I walk with the numbers uh then I I put it in that image that I would upload and use for the CTF challenge so that's really all it is that that executable who put this here was that source code that I would print out the flag and the way that you can include that inside of the image is by actually catting it one after the other because cat will look will output these files in sequence and typically an image viewer once it sees the end of an image it just goes oh that's that's really all that the image is it just displays the image no problem at all but you can use binwalk to see are is there anything more inside this file in which case we had a complete Program stuck inside the image so that's why I wanted to introduce binwalk as a tool if they hadn't seen it before if they if they if they have not heard of it so that's how you ended up solving and creating that one that's a Brisk stroll and we'll move on to some more of these challenges in a future video so thanks for watching guys