backdoor CTF evil

backdoor CTF evil

hi today we going to solve CTF challenge   let us quick read  it

link

cool it's service on port 9007 now  time to read source code 

  

now we going to explain how code flow work flag define as variable and also super_secret_code that it's part one now going to part 2 it's condition flow first guess it take inputs using python input and compare it with super_secret_code if condition true it will print flag .

ok that flow now time to identify weakness ,input in last python version it act like  eval(raw_input) as we know eval it    function evaluates a string of text which is passed as its parameter, accepting possible second argument for the global values to use during evaluation.

through this we can read super_secret_code by type it in prompt it will read variable and save it in guess and use it in if statement .

quick example

you see we enter secret again now let us print g to see what inside it 

nice we have secret key now let go  do that in real connect to host using netcat 

and type super_secret_code

for more info about input read python input vulnerability 

thanks for reading 

@intx0x80