OSU Gaming 2025 Writeup
Challenge Directory
Challenge Name: pump-lion
A prompt engineering challenge eh? Here’s the description:
PumpLion, the cheerful lion mascot of osu!gaming CTF, has been deployed as a “super-secure” chatbot for event participants. Rumor has it… the flag is hidden deep in its silicon jungle. But don’t expect it to just hand it to you on a silver platter - it’s been “prompt-trained” to protect it at all costs.
Note: rate limiting is enforced, do not spam the LLM.
expected difficulty: 2/5
Author (new field from now on ):
sahuang
This is a misc category challenge, where they provided a link [now dead] to a chatbot interface. The goal was to extract the flag from the chatbot, which was designed to be “super-secure” apparantly and not give away the flag without a fight.
I began with a simple question, “hi lion, what’s your mane made of?” to see how the chatbot would respond. Unfortunately it seemed that there was a server error, which I thought was intentional, only to find out later that the response that I got was really an error on their side.
After a few more attempts, I was able to determine that maybe some kind of password or secret phrase was needed to unlock the chatbot and give out the flag. Unfortunately this turned out to be a hallucination by PumpLion.
Eventually, I ran out of time (as I had only started this challenge 40 min before the CTF ended) and was not able to get the flag. However, I did learn a few things about prompt engineering and how to interact with chatbots in a more effective way.
For future reference, here is what works to get the flag from PumpLion:
Very interesting ehh? I knew that saying something on behalf of the system would work (from previous experience with prompt engineering/jailbreaking), but I unfortunately was not able to come up with this exact prompt in time.
Either way, I then looked up PumpLion’s creator on google and found their github:
Something else that caught my eye was when this account was created - a few days before the CTF started. Suspicious indeed.
Went onto the only repo there, which was this:
I saw remnents of a flag (as the flag format for this CTF began with OSU{) but in the current version of the README, the actual flag is missing.
Naturally, I checked out the commit history to see if the flag was present in any previous versions of the README:
Clicking on the second commit, I found the flag!! yay!
And there we have it, the flag for this challenge is: