Loose Strings

Challenge description:

Apperantly there’s a flag in this binary, but we can’t find it. Can you?

Let’s run it and see what it has to say for itself.

❯ ./main | sort | uniq -c
    403 I wonder what the flag is?

Yeah, me too buddy. It prints the same line 403 times, and then it quits. That’s it, that’s the whole program.

With a name like Loose Strings, I think we can skip the fancy tools for now and start with strings. It pulls out anything in a file that looks like readable text, so it’s always a good first move on a binary. And since we know the flag format, we can use grep to cut through the noise.

❯ strings main | grep STOUTCTF
STOUTCTF{yMShsEOJtQZx4HK6krhkkPgNPQMugq4m}

Well that was fast.

If you open it in Ghidra you can see why you’d never find this by running it. The whole main function is just 403 calls to puts, and the flag never gets used anywhere. It’s just sitting in the binary, doing nothing, waiting for someone to look.

FLAG: STOUTCTF{yMShsEOJtQZx4HK6krhkkPgNPQMugq4m}