Snake
Description: Can you slither to the win?
Link to the binary: Elf file
Introduction
We are faced with a binary file written in Rust (you can see it by simply running strings snake | grep rustc) where we are made to play Snake, the goal is to get PRECISELY to 16525 points.
Solution
The solutions were actually different, some people used tools to analyze the memory of a process in real time, I preferred a ‘slower’ approach, or rather the first thing that came to mind, so I opened binary ninja despite the file being stripped and looked for a value for constant exactly 0xa (i.e. the value that was added every time it ate a #).
In a short time I managed to find this:
After some trial and error, changing the value from 0xa to 0xb, I find the line of code I need, which is the last one in the screenshot above.
At this point I switch to the assembly and notice that my initial approach was wrong this is because I was putting too high a value in a register that it did not support in fact analysing the binary in assembly we see:
As we can see, before entering the constant into the dword register [rcx+0x7c], we first enter it into eax and if we enter too high a value, the programme simply crashes (as it should).
So simply afterwards I chose to put the precise value in the correct register once I had made at least one point
(the nop are automatically inserted by binary ninja)
In this way, once we have scored at least one point, we will have the flag
Author: akiidjk