The main idea finding the flag is exploiting the Buffer Overflow of the Binary file.
After logging into the remote access with ssh [email protected] -p 1001 and password as guest,
my system got completely crashed due to several DDoS attacks. So, I directly looked up for solution and understood from there.
https://www.embeddedhacker.com/2020/01/hacking-walkthrough-ctflearn-binary-medium/
Finally the flag becomes:
flag{c0lor_0f_0verf1ow}