---
# System prepended metadata

title: GreyCTF 2025 Qualifiers Challenge Backup Sheet

---

## Web
### C2
Our forensics teams have discovered this Golang command and control server on a compromised system.

Can you exfiltrate the flag?

``` http://challs.nusgreyhats.org:33203 ```

https://storage.googleapis.com/greyctf25-challs/dist-c2.zip



### Sgrpc
Can't get hacked if they can't reach it.

``` http://challs.nusgreyhats.org:33202 ```

https://storage.googleapis.com/greyctf25-challs/dist-sgrpc.zip



### Hft
Alice Avenue has built a new exchange for trading flags!

Can you beat their insider trading algorithms?

``` http://challs.nusgreyhats.org:33201 ```

https://storage.googleapis.com/greyctf25-challs/dist-hft.zip



### Rainbow Road
Greycat's been feeling kind of blue lately, find the hidden message to cheer him up!

``` http://challs.nusgreyhats.org:33204 ```

https://storage.googleapis.com/greyctf25-challs/dist-rainbow-road.zip

## Misc
### Countle Training Centre
The Countle World Championships is coming! Time to step up your game and start training! It's just a measly 1,000,000 puzzles a day, anyone can do it.

``` nc challs.nusgreyhats.org 33401 ```

https://storage.googleapis.com/greyctf25-challs/dist-countle_training_centre.zip



### Subgb
My friend sent me this image. What the ***k am I suppose to do with it?!??

https://storage.googleapis.com/greyctf25-challs/dist-subGB.zip



### Elijahs Sequential Ctf
I created a fairly easy competitive programming problem to test your algorithm coding skills. Please only use python3, c and cpp.

The remote judge compiles cpp code using `g++ -DONLINE_JUDGE -fno-tree-ch -O2 -Wall -std=c++14`, c code using `gcc -DONLINE_JUDGE -fno-tree-ch -O2 -Wall -std=c99` and runs python3 code using `python3.7.8`.

Good luck and remember to flush your outputs! The rest of the information is in the pdf :)

backup: `34.41.69.139 5000`

``` nc 35.198.201.39 33402 ```

https://storage.googleapis.com/greyctf25-challs/dist-elijahs_sequential_ctf.zip



### Secret Development Kit
You have just stolen top secret production files of a secret board. Hmm, I wonder what it could be?

https://storage.googleapis.com/greyctf25-challs/dist-secret-development-kit.zip

## Rev
### Sksksk
My friend Alonzo texts with sksksk all the time, the other day he sent me this strange looking JavaScript file.

https://storage.googleapis.com/greyctf25-challs/dist-sksksk.zip



### Meowware
I got infected. Help me find out what was stolen!

https://storage.googleapis.com/greyctf25-challs/dist-meowware.zip



### Thecatshop
My friend from Greyhats sent me this cool game depicting the Greyhat Summit. He told me there's a flag waiting for me when I finish the game, but I can't do it! Can you help me?

Note: After you've found the flag, submit all alphabetical characters in lowercase.

https://storage.googleapis.com/greyctf25-challs/dist-thecatshop.zip



### Whr Cat
My cat got encrypted, can you help to recover my cat :(

(After recovering the flag, run strings <recovered flag> | grep grey to get the flag)

https://storage.googleapis.com/greyctf25-challs/dist-whr_cat.zip

## Osint
### Red Flag Recon
Since announcing GreyCTF, we've noticed persistent comments on the GreyHats Instagram account from a user keen to create a challenge for us. But with GreyCTF so close to our final exams, we haven't had the bandwidth to properly vet him. Help us check him out, make sure there are no red flags.

Note: There is only one flag in this challenge. If it fits the flag format `grey{...}`, you've likely got it!



### By The Banana Tree
I saw a church in the distance while travelling. Can you tell me where it is?

The flag consists of latitude and longitude coordinates of the location where the photo was taken, rounded to three decimal places, and the name of the church in the distance in lowercase (according to google maps, omitting any potential spaces, punctuation and diacritics).

Regarding flag format, consider this example for Notre Dame de Paris: `grey{N48-853_E2-349_notredamecathedralofparis}`

https://storage.googleapis.com/greyctf25-challs/dist-by_the_banana_tree.zip



### Like Comment Subscribe
nus.greyhats have decided that social media is a good place to share the message!

## Forensics
### Layer Cake
Layer cake is so good. I have an mp3 file all about layer cake. Maybe you can find the flag there?

https://storage.googleapis.com/greyctf25-challs/dist-layer-cake.zip

### A Walk in the Park
Warm up your OSINT skills with this challenge!

You are given an image of a sign in the park.

Submit the text on the sign as the flag in lowercase, converting all new lines and spaces to underscores.

For example, if the sign looks like this:


ABC PARK

123 Main St. 

Singapore

Then, submit the flag as grey{abc_park_123_main_st_singapore}.

https://storage.googleapis.com/greyctf25-challs/dist-a_walk_in_the_park.zip


### Notsus.Exe
\<Insert Guessy forensics challenge description here>

https://storage.googleapis.com/greyctf25-challs/dist-notsus.exe.zip



### Connection Issues
One of our employees was browsing the web when he suddenly lost connection! Can you help him figure out why?

https://storage.googleapis.com/greyctf25-challs/dist-connection-issues.zip

## Ezpz
### Baby Bytes
Here's a beginner pwn challenge for all my baby pwners! Overwrite the saved return address to the address of the win function, and enjoy your shell! :D

``` nc challs.nusgreyhats.org 33021 ```

https://storage.googleapis.com/greyctf25-challs/dist-baby_bytes.zip



### Tung Tung Tung Sahur
New to the world of brainrot? Not sure what names to pick from? We've got you covered with a list of our faves:

- Tralalero Tralala

- Chef Crabracadabra

- Boneca Ambalabu

- Tung Tung Tung Tung Tung Tung Tung Tung Tung Sahur

https://storage.googleapis.com/greyctf25-challs/dist-tung_tung_tung_sahur.zip

### Reversing 101
All reverse engineers have to start somewhere. If you have never reverse-engineered before, its time to take your first step!

```nc challs.nusgreyhats.org 33000```
    
https://storage.googleapis.com/greyctf25-challs/dist-Reversing_101.zip
    
### oops
    
Simple URL shortener. What could go wrong?

http://challs.nusgreyhats.org:33001/

https://storage.googleapis.com/greyctf25-challs/dist-oops.zip
    
## Crypto
### Not A Permutation Matrix
```

I got a permute, I got a matrix,

<insert questionable sound>

permute matrix.

```

https://storage.googleapis.com/greyctf25-challs/dist-not-a-permutation-matrix.zip



### Idk
I've been really into zero knowledge proofs lately! I wrote a simple program that can prove that I'm the only person who knows how to decrypt this message, and because I'm so confident, I'll even give you some dumps of my proofs!

https://storage.googleapis.com/greyctf25-challs/dist-idk.zip



### Shaker
You found a shaker. Can you get the flag out?

``` nc challs.nusgreyhats.org 33302 ```

https://storage.googleapis.com/greyctf25-challs/dist-shaker.zip



### Uwusignatures
As an uwu girl, I decided to make this digital signature scheme to share my signatures with everyone!

I'll only show you half of my signature though, because I'm shy...

Surely, no one would steal from a cutie like myself... right?

``` nc challs.nusgreyhats.org 33301 ```

https://storage.googleapis.com/greyctf25-challs/dist-uwusignatures.zip

## Blockchain
### Launchpad
Since token launchpads are the new trend nowadays, we decided to write our own! Will grey.fun be the next billion dollar protocol?

``` nc challs.nusgreyhats.org 33501 ```

https://storage.googleapis.com/greyctf25-challs/dist-launchpad.zip



### Rational
We re-implemented ERC4626 to perform calculations in rational numbers. Rounding issues, begone!

``` nc challs.nusgreyhats.org 33503 ```

https://storage.googleapis.com/greyctf25-challs/dist-rational.zip

## Pwn
### Adversarial Beaver
It's so amazing how they [solved BB-5](https://www.youtube.com/watch?v=rmx3FBPzDuk).

Let's see how well each team can do on BB-100!

``` nc challs.nusgreyhats.org 33103 ```

https://storage.googleapis.com/greyctf25-challs/dist-adversarial_beaver.zip



### Infinite Connect Four
I was playing some connect four with my friend Elma but the games were too trivial... So I decided to create a new game, infinite connect four! He'll never see his demise coming!

``` nc challs.nusgreyhats.org 33102 ```

https://storage.googleapis.com/greyctf25-challs/dist-infinite_connect_four.zip



### Vexed
this problem is vexing me, i require the assistance of a master of the VEX prefix!

``` nc challs.nusgreyhats.org 33101 ```

https://storage.googleapis.com/greyctf25-challs/dist-vexed.zip

