L’inspiration en images
In this challenge, we have access to two file vue_sur_un_etrange_tableau (binary executable file) and verso.txt (text file). Like in the challenge said, we do not need to worry about the file verso.txt because it will not help to find the flag. So I decided to use Ghidra to look at the binary and find something interesting.
It looks like this file is very complicated and main function contains a lot of variables as shown below.
As the challenge mentioned, we just need to find the parameters corresponding to the background color of this challenge so I’m not trying to read the code but just learn a few things who allows me to find the flag.
After conducting some research on Google, I discovered that this binary file utilizes the GLFW engine for its images and animations. As a result, I can explore the GLFW documentation to identify the function responsible for modifying the background color. I can then search for this function within Ghidra to locate the corresponding parameter for the color of the background.
After some further searching in the GLFW documentation, I found that the function glClearColor() can be used to change the background color. Therefore, I have decided to search for this function within Ghidra to locate its implementation and relevant parameters.
After clicking on the line XREF[1] (green text on the right as shown above), I found a string used to call this function as shown below
Now let’s try to search for the string “glad_glClearColor” in the functions. Fortunately, we have it in the main function.
It is evident that the four hexadecimal numbers 0x3e4ccccd, 0x3e99999a, 0x3e99999a, and 0x3f800000 correspond to the parameters for the background color. However, to adhere to the requirement of representing them as real numbers with one digit after the decimal point, I utilized the gregstoll website to perform the conversion.
Flag: 404CTF{vec4(0.2,0.3,0.3,1.0)}