When we run the program, we are prompted to enter the flag. If we enter something, the program prints wrong! and exits. Presumably, the goal of the challenge is to reverse engineer the program to figure out what input string will cause the program to print something other than wrong!.
strings is a useful program that can be used to quickly find hardcoded strings (and secrets!) in binary files. In this challenge however, running strings does not find the flag as one might expect from the challenge name. Here are two (among many other) ways to solve the challenge:
- Running
xxdand looking through the output reveals something that resembles the flag (which we can recognise from theDUCTF{flag format) - Opening the binary in
radare2and running theizcommand to print strings in the data sections of the binary